20-F/A

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 20-F/A

(Mark One)

☐ REGISTRATION STATEMENT PURSUANT TO SECTION 12(b) OR (g) OF THE SECURITIES EXCHANGE ACT OF 1934

OR

☒ ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the fiscal year ended 31 March 2018

OR

☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

OR

☐ SHELL COMPANY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

Date of event requiring this shell company report                     

For the transition period from                      to                     

Commission File Number: 2-94004

British Telecommunications plc

(Exact name of Registrant as specified in its charter)

Not Applicable	England and Wales
(Translation of Registrant’s name into English)	(Jurisdiction of incorporation or organization)

BT Centre

81 Newgate Street, London, EC1A 7AJ

England

(address of principal executive offices)

BT Americas Inc.

8951 Cypress Waters Blvd

Suite 200

Dallas, TX 75019

United States

FAO: Richard Nohe, Vice President and Chief Counsel North America

(203) 461-8098

(Name, Telephone, E-mail and/or Facsimile number and Address of Company Contact Person)

Securities registered or to be registered pursuant to Section 12(b) of the Act:

Securities registered or to be registered pursuant to Section 12(g) of the Act: None

Securities for which there is a reporting obligation pursuant to Section 15(d) of the Act:

$2,670,000,000 9.125% Notes Due 2030

$800,000,000 2.35% Senior Notes Due 2019

Indicate the number of outstanding shares of each of the issuer’s classes of capital or common stock as of the close of the period covered by the annual report:

8,689,755,905 Ordinary Shares, of 25p each

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act.    Yes  ☒    No  ☐

If this report is an annual or transition report, indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934.    Yes  ☐    No  ☒

Note — Checking the box above will not relieve any registrant required to file reports pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 from their obligation under those Sections.

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  ☒    No  ☐

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  ☐    No  ☐

Not Applicable

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or an emerging growth company. See definition of “large accelerated filer,” “accelerated filer,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

Large accelerated filer	☐	Accelerated filer	☐
Non-accelerated filer	☒	Emerging growth company	☐

If an emerging growth company that prepares its financial statements in accordance with U.S. GAAP, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards† provided pursuant to Section 13(a) of the Exchange Act. ☐

† The term “new or revised financial accounting standard” refers to any update issued by the Financial Accounting Standards Board to its Accounting Standards Codification after April 5, 2012.

Indicate by check mark which basis of accounting the registrant has used to prepare the financial statements included in this filing:

U.S. GAAP  ☐ International Financial Reporting Standards as issued by the International Accounting Standards Board  ☒ Other  ☐

If “Other” has been checked in response to the previous question indicate by check mark which financial statement item the registrant has elected to follow.    Item 17  ☐    Item 18  ☐

If this is an annual report, indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).     Yes  ☐    No  ☒

(APPLICABLE ONLY TO ISSUERS INVOLVED IN BANKRUPTCY PROCEEDINGS DURING THE PAST FIVE YEARS)

Indicate by check mark whether the registrant has filed all documents and reports required to be filed by Sections 12, 13 or 15(d) of the Securities Exchange Act of 1934 subsequent to the distribution of securities under a plan confirmed by a court.    Yes  ☐    No  ☐

Not Applicable

As a wholly-owned subsidiary of BT Group plc, a public company with limited liability incorporated in the United Kingdom and which has its registered office in England, British Telecommunications plc meets the conditions set forth in General Instruction I(1)(a) and (b) of Form 10-K, as applied to reports on Form 20-F, and is therefore filing its Form 20-F with a reduced disclosure format.

Explanatory Note

This Amendment No. 1 to Form 20-F (“Form 20-F/A” or Amendment No. 1”) amends the annual report for the year ended 31 March 2018 of British Telecommunications plc, which was filed with the Securities and Exchange Commission on 24 May 2018 (the “Original 2018 Form 20-F”). British Telecommunications plc is filing this Amendment No. 1 solely to furnish Exhibit 101, which was not included in the Original 2018 Form 20-F. Exhibit 101 includes information in eXtensible Business Reporting Language (XBRL).

Except as described above, this Amendment No. 1 does not amend any information set forth in the Original 2018 Form 20-F, and British Telecommunications plc has not updated disclosures included therein to reflect any events that occurred subsequent to 24 May 2018.

Pursuant to Rule 406T of Regulation S-T, these interactive data files are deemed furnished and not filed or part of a registration statement or prospectus for purposes of Sections 11 or 12 of the Securities Act of 1933, as amended, and are deemed not filed for purposes of Section 18 of the Securities and Exchange Act of 1934, as amended, and are otherwise not subject to liability under those sections.

PART III

Item 19. Exhibits.

Exhibit Number	Description of Exhibit
101	(1) Consolidated Balance Sheets as of 31 December 2017 and 2016;
	(2) Consolidated Statements of Income for the years ended 31 December 2017, 2016 and 2015;
	(3) Consolidated Statements of Cash Flows for the years ended 31 December 2017, 2016 and 2015;
	(4) Consolidated Statements of Equity for the years ended 31 December 2017, 2016 and 2015; and
	(5) Notes to Consolidated Financial Statements.

SIGNATURES

The registrant hereby certifies that it meets all of the requirements for filing on Form 20-F/A and that it has duly caused and authorized the undersigned to sign this annual report on its behalf.

BRITISH TELECOMMUNICATIONS plc
By:	/s/ Simon Lowth
Name:	Simon Lowth
Title:	Principal Financial Officer

Date: June 22, 2018

XML

Document and Entity Information	12 Months Ended
	Mar. 31, 2018 shares
Document Information [Line Items]
Document Type	20-F/A
Amendment Flag	false
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Registrant Name	BRITISH TELECOMMUNICATIONS PLC /ADR
Entity Central Index Key	0000820534
Current Fiscal Year End Date	--03-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding	8,689,755,905

XML

Group income statement - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statements [Line Items]
Revenue		£ 23,723	£ 24,062	£ 19,012
Operating costs		(20,339)	(20,892)	(15,397)
Operating profit (loss)		3,384	3,170	3,615
Finance expense		(794)	(842)	(769)
Finance income		215	232	389
Net finance expense	[1]	(579)	(610)	(380)
Share of post tax profit (loss) of associates and joint ventures		(1)	(9)	6
Profit (loss) before taxation		2,804	2,551	3,241
Taxation		(620)	(485)	(508)
Profit (loss) for the year		2,184	2,066	2,733
Before Specific Items [Member]
Statements [Line Items]
Revenue	[2]	23,746	24,082	18,879
Operating costs		(19,752)	(19,944)	(15,052)
Operating profit (loss)	[2]	3,994	4,138	3,827
Finance expense		(576)	(632)	(540)
Finance income		215	232	389
Net finance expense		(361)	(400)	(151)
Share of post tax profit (loss) of associates and joint ventures		(1)	(9)	6
Profit (loss) before taxation		3,632	3,729	3,682
Taxation		(707)	(702)	(674)
Profit (loss) for the year		2,925	3,027	3,008
Specific Items [Member]
Statements [Line Items]
Revenue	[3]	(23)	(20)	133
Operating costs	[3]	(587)	(948)	(345)
Operating profit (loss)	[3]	(610)	(968)	(212)
Finance expense	[3]	(218)	(210)	(229)
Net finance expense	[3]	(218)	(210)	(229)
Profit (loss) before taxation	[3]	(828)	(1,178)	(441)
Taxation	[3]	87	217	166
Profit (loss) for the year	[3]	£ (741)	£ (961)	£ (275)

[1] Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

[2] Before specific items.

[3] a For a definition of specific items, see page 209. An analysis of specific items is provided in note 8.

XML

Group statement of comprehensive income - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statement Of Comprehensive Income [Abstract]
Profit for the year	£ 2,184	£ 2,066	£ 2,733
Items that will not be reclassified to the income statement
Remeasurements of the net pension obligation	2,160	(2,789)	755
Tax on pension remeasurements	(346)	416	(240)
Items that have been or may be reclassified to the income statement
Exchange differences on translation of foreign operations	(188)	237	29
Fair value movement on available-for-sale assets	11	(3)	(2)
Fair value movement on cash flow hedges:
– net fair value (losses) gains	(368)	884	381
– recognised in income and expense	277	(938)	(230)
Tax on components of other comprehensive income that have been or may be reclassified	1	29	5
Other comprehensive income (loss) for the year, net of tax	1,547	(2,164)	698
Total comprehensive income (loss) for the year	£ 3,731	£ (98)	£ 3,431

XML

Group balance sheet - GBP (£) £ in Millions		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Non-current assets
Intangible assets		£ 14,455	£ 15,037	£ 15,458
Property, plant and equipment		17,000	16,498	15,971
Derivative financial instruments		1,312	1,818	1,462
Investments		13,354	11,606	11,965
Associates and joint ventures		38	31	24
Trade and other receivables	[1]	317	360	218
Deferred tax assets		1,243	1,717	1,247
Non current assets		47,719	47,067	46,345
Current assets
Programme rights		272	264	225
Inventories		239	227	189
Trade and other receivables		4,029	3,860	3,987
Current tax receivable		77	73	65
Derivative financial instruments		197	428	177
Investments		3,224	1,740	3,271
Cash and cash equivalents		521	526	989
Current assets		8,559	7,118	8,903
Current liabilities
Loans and other borrowings		2,298	2,791	3,756
Derivative financial instruments		50	34	48
Trade and other payables		7,190	7,476	7,463
Current tax liabilities		83	197	271
Provisions		603	625	178
Current liabilities		10,224	11,123	11,716
Total assets less current liabilities		46,054	43,062	43,532
Non-current liabilities
Loans and other borrowings		13,038	11,105	12,029
Derivative financial instruments		787	869	863
Retirement benefit obligations		6,371	9,088	6,382
Other payables		1,326	1,298	1,106
Deferred tax liabilities		1,340	1,240	1,262
Provisions		452	536	565
Non current liabilities		23,314	24,136	22,207
Equity
Ordinary shares		2,172	2,172	2,172
Share premium		8,000	8,000	8,000
Other reserves		1,241	1,591	1,392
Retained earnings		11,327	7,163	9,761
Total shareholder’s equity		22,740	18,926	21,325
Total equity and Liabilities		£ 46,054	£ 43,062	£ 43,532

[1] Other assets includes costs relating to the initial set-up, transition or transformation phase of long-term networked IT services contracts of £145m (2016/17: £163m, 2015/16: £111m), and prepayments and leasing debtors of £172m (2016/17: £197m, 2015/16: £107m).

XML

Group statement of changes in equity - GBP (£) £ in Millions	Total	Issued Capital [Member]	[1]	Share Premium [Member]	[2]	Other Reserves [Member]	[3]	Retained Earnings (Loss) [Member]
Beginning balance at Mar. 31, 2015	£ 19,277	£ 2,172		£ 8,000		£ 1,209		£ 7,896
Statements [Line Items]
Profit for the year	2,733							2,733
Other comprehensive income (loss) – before tax	1,163					408		755
Tax on other comprehensive income (loss)	(235)					5		(240)
Transferred to the income statement	(230)					(230)
Total comprehensive income (loss) for the year	3,431					183		3,248
Share-based payments	58							58
Tax on share-based payments	12							12
Dividends to parent company	(1,450)							(1,450)
Other movements	(3)							(3)
Ending balance at Mar. 31, 2016	21,325	2,172		8,000		1,392		9,761
Statements [Line Items]
Profit for the year	2,066							2,066
Other comprehensive income (loss) – before tax	(1,671)					1,108		(2,779)
Tax on other comprehensive income (loss)	445					29		416
Transferred to the income statement	(938)					(938)
Total comprehensive income (loss) for the year	(98)					199		(297)
Share-based payments	57							57
Tax on share-based payments	(6)							(6)
Dividends to parent company	(2,350)							(2,350)
Other movements	(2)							(2)
Ending balance at Mar. 31, 2017	18,926	2,172		8,000		1,591		7,163
Statements [Line Items]
Profit for the year	2,184							2,184
Other comprehensive income (loss) – before tax	1,615					(545)		2,160
Tax on other comprehensive income (loss)	(345)					1		(346)
Transferred to the income statement	277					277
Total comprehensive income (loss) for the year	3,731					(267)		3,998
Transfers to realised profit						(83)		83
Share-based payments	84							84
Tax on share-based payments	(2)							(2)
Other movements	1							1
Ending balance at Mar. 31, 2018	£ 22,740	£ 2,172		£ 8,000		£ 1,241		£ 11,327

[1] The allotted, called up, and fully paid ordinary share capital of the company at 31 March 2018 was £2,172m comprising 8,689,755,905 ordinary shares of 25p each.

[2] The share premium account, comprising the premium on allotment of shares, is not available for distribution.

[3] For further analysis of other reserves, see note 26.

XML

Group statement of changes in equity (Parenthetical) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Statements [Line Items]
Ordinary shares	£ 22,740	£ 18,926	£ 21,325	£ 19,277
Number of ordinary shares	8,689,755,905
Par value per share	£ 0.25
Issued Capital [Member]
Statements [Line Items]
Ordinary shares	£ 2,172

XML

Group cash flow statement - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Cash flow from operating activities
Profit (loss) before taxation		£ 2,804	£ 2,551	£ 3,241
Share of post tax loss (profit) of associates and joint ventures		1	9	(6)
Net finance expense	[1]	579	610	380
Operating profit (loss)		3,384	3,170	3,615
Other non-cash charges		33	20	39
Profit on disposal of businesses		(1)	(16)
Depreciation and amortisation		3,514	3,572	2,631
Increase in inventories		(14)	(33)
Increase in programme rights		(34)	(95)	(44)
(Increase) decrease in trade and other receivables	[2]	(156)	168	(83)
(Decrease) increase in trade and other payables		(367)	(150)	123
Decrease in other liabilities	[3]	(775)	(307)	(810)
(Decrease) increase in provisions	[4]	(203)	401	(63)
Cash generated from operations		5,381	6,730	5,408
Income taxes paid		(473)	(551)	(256)
Net cash inflow from operating activities		4,908	6,179	5,152
Cash flow from investing activities
Interest received		7	7	10
Dividends received from associates and joint ventures			2	17
Acquisition of subsidiaries	[5]	(16)	18	93
Proceeds on disposal of subsidiaries, associates and joint ventures	[5]	2	46
Acquisition of joint ventures		(9)	(13)	(8)
Outflow on non-current amounts owed by ultimate parent company	[6]	(1,677)	(1,571)	(4,767)
Proceeds on disposal of current financial assets	[7]	11,134	10,834	8,918
Purchases of current financial assets	[7]	(12,629)	(9,411)	(8,252)
Proceeds on disposal of non-current asset investments	[8]	19
Purchases of non-current asset investments	[8]		(22)
Proceeds on disposal of property, plant and equipment		21	26	7
Purchases of property, plant and equipment and software		(3,362)	(3,145)	(2,438)
Net cash outflow from investing activities		(6,510)	(3,229)	(6,420)
Cash flow from financing activities
Interest paid		(555)	(629)	(558)
Repayment of borrowings	[9]	(1,401)	(1,805)	(1,283)
Proceeds from bank loans and bonds		3,760	3	3,023
Cash flows from derivatives related to net debt		(188)	119	79
Drawdown on acquisition facility				3,200
Repayment of acquisition facility			(181)	(3,019)
Repayment of EE revolving credit facility			(438)	(100)
Net cash inflow (outflow) from financing activities		1,616	(2,931)	1,342
Net increase in cash and cash equivalents		14	19	74
Opening cash and cash equivalents	[10]	509	452	402
Net increase in cash and cash equivalents		14	19	74
Effect of exchange rate changes		(31)	38	(24)
Closing cash and cash equivalents	[10]	£ 492	£ 509	£ 452

[1] Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

[2] Includes a prepayment of £325m (2016/17: £nil, 2015/16: £nil) in respect of the acquisition of Spectrum.

[3] Includes pension deficit payments of £872m (2016/17: £274m, 2015/16: £880m).

[4] Included within the change in provisions is the settlement of Deemed Consent, part of which is non-cash and is offset by movements in working capital.

[5] Acquisitions and disposals of subsidiaries are shown net of cash acquired or disposed of and in 2017 included £20m true-up of consideration following the audit of the completion balance sheet relating to the acquisition of EE.

[6] Refer to note 28 for further information.

[7] Primarily consists of investment in and redemption of amounts held in liquidity funds.

[8] Relates to assets held for sale classified within trade and other receivables.

[9] Repayment of borrowings includes the impact of hedging and repayment of lease liabilities.

[10] Net of bank overdrafts of £29m (2016/17: £17m, 2015/16: £537m).

XML

Group cash flow statement (Parenthetical) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statements [Line Items]
Pension deficit payments	£ 872	£ 274	£ 880
Acquisitions and disposals of subsidiaries true-up of consideration		20
Net of bank overdrafts	29	£ 17	£ 537
Spectrum [Member]
Statements [Line Items]
Prepayments in respect of acquisition	£ 325

XML

Group plc balance sheet - GBP (£) £ in Millions		Mar. 31, 2018	Mar. 31, 2017
Non-current assets
Intangible assets		£ 14,455	£ 15,037
Property, plant and equipment		17,000	16,498
Derivative financial instruments		1,312	1,818
Associates and joint ventures		38	31
Trade and other receivables	[1]	317	360
Deferred tax assets		1,243	1,717
Non current assets		47,719	47,067
Current assets
Programme rights		272	264
Inventories		239	227
Trade and other receivables		4,029	3,860
Current tax receivable		77	73
Derivative financial instruments		197	428
Cash and cash equivalents		521	526
Current assets		8,559	7,118
Current liabilities
Loans and other borrowings		2,298	2,791
Derivative financial instruments		50	34
Trade and other payables		7,190	7,476
Provisions		603	625
Current liabilities		10,224	11,123
Total assets less current liabilities		46,054	43,062
Non-current liabilities
Loans and other borrowings		13,038	11,105
Derivative financial instruments		787	869
Retirement benefit obligations		6,371	9,088
Other payables		1,326	1,298
Deferred tax liabilities		1,340	1,240
Provisions		452	536
Non current liabilities		23,314	24,136
Equity
Ordinary shares		2,172	2,172
Share premium		8,000	8,000
Other reserves		1,241	1,591
Retained earnings		11,327	7,163
Total shareholder’s equity		22,740	18,926
Total equity and Liabilities		46,054	43,062
British Telecommunications plc [Member]
Non-current assets
Intangible assets		2,031	1,954
Property, plant and equipment		13,995	13,558
Derivative financial instruments		1,312	1,818
Associates and joint ventures		23,889	27,554
Other investments		14,805	13,881
Trade and other receivables		134	177
Deferred tax assets		1,044	1,504
Non current assets		57,210	60,446
Current assets
Programme rights		272	264
Inventories		72	89
Trade and other receivables		2,300	2,077
Current tax receivable		217	3
Derivative financial instruments		201	425
Other investments		5,748	5,036
Cash and cash equivalents		288	286
Current assets		9,098	8,180
Current liabilities
Loans and other borrowings		18,494	19,999
Derivative financial instruments		50	33
Trade and other payables		4,239	4,178
Provisions		428	539
Current liabilities		23,211	24,749
Total assets less current liabilities		43,097	43,877
Non-current liabilities
Loans and other borrowings		14,916	16,874
Derivative financial instruments		787	869
Retirement benefit obligations		5,958	8,632
Other payables		1,888	1,801
Deferred tax liabilities		918	871
Provisions		291	323
Non current liabilities		24,758	29,370
Equity
Ordinary shares		2,172	2,172
Share premium		8,000	8,000
Other reserves		703	857
Retained earnings		7,464	3,478
Total shareholder’s equity		18,339	14,507
Total equity and Liabilities		£ 43,097	£ 43,877

[1] Other assets includes costs relating to the initial set-up, transition or transformation phase of long-term networked IT services contracts of £145m (2016/17: £163m, 2015/16: £111m), and prepayments and leasing debtors of £172m (2016/17: £197m, 2015/16: £107m).

XML

Group plc balance sheet (Parenthetical) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statements [Line Items]
Cash	£ 439,000,000	£ 467,000,000
Cash equivalents	82,000,000	59,000,000
Dividends to shareholders		2,350,000,000
British Telecommunications plc [Member]
Statements [Line Items]
Cash	232,000,000	253,000,000
Cash equivalents	56,000,000	33,000,000
Dividends received	2,057,000,000	1,351,000,000
Dividends to shareholders	£ 0	£ 2,350,000,000

XML

Group plc statement of changes in equity - GBP (£)	Total	Share Capital [Member]	[1]	Share Premium [Member]	[2]	Other Reserves [Member]	[3]	Retained Earnings [Member]	British Telecommunications plc [Member]		British Telecommunications plc [Member] Share Capital [Member]	[4]	British Telecommunications plc [Member] Share Premium [Member]	[5]	British Telecommunications plc [Member] Other Reserves [Member]	[6]	British Telecommunications plc [Member] Retained Earnings [Member]
Beginning balance at Mar. 31, 2015	£ 19,277,000,000	£ 2,172,000,000		£ 8,000,000,000		£ 1,209,000,000		£ 7,896,000,000
Statements [Line Items]
Profit for the year	2,733,000,000							2,733,000,000
Share-based payments	58,000,000							58,000,000
Tax on share-based payments	12,000,000							12,000,000
Dividends to parent company	(1,450,000,000)							(1,450,000,000)	£ (1,450,000,000)
Ending balance at Mar. 31, 2016	21,325,000,000	2,172,000,000		8,000,000,000		1,392,000,000		9,761,000,000	17,760,000,000		£ 2,172,000,000		£ 8,000,000,000		£ 900,000,000		£ 6,688,000,000
Statements [Line Items]
Profit for the year	2,066,000,000							2,066,000,000	1,351,000,000	[7]							1,351,000,000	[7]
Actuarial gain (loss)									(2,659,000,000)								(2,659,000,000)
Tax on actuarial loss									419,000,000								419,000,000
Share-based payments	57,000,000							57,000,000	44,000,000								44,000,000
Tax on share-based payments	(6,000,000)							(6,000,000)	(6,000,000)								(6,000,000)
Tax on items taken directly to equity									6,000,000						6,000,000
Increase (decrease) in fair value of cash flow hedges									790,000,000						790,000,000
Dividends to parent company	(2,350,000,000)							(2,350,000,000)	(2,350,000,000)								(2,350,000,000)
Transferred to the income statement									(839,000,000)						(839,000,000)
Other									(9,000,000)								(9,000,000)
Ending balance at Mar. 31, 2017	18,926,000,000	2,172,000,000		8,000,000,000		1,591,000,000		7,163,000,000	14,507,000,000		2,172,000,000		8,000,000,000		857,000,000		3,478,000,000
Statements [Line Items]
Profit for the year	2,184,000,000							2,184,000,000	2,057,000,000	[7]							2,057,000,000	[7]
Actuarial gain (loss)									2,142,000,000								2,142,000,000
Tax on actuarial loss									(365,000,000)								(365,000,000)
Share-based payments	84,000,000							84,000,000	71,000,000								71,000,000
Tax on share-based payments	(2,000,000)							(2,000,000)	(1,000,000)								(1,000,000)
Tax on items taken directly to equity									12,000,000						12,000,000
Increase (decrease) in fair value of cash flow hedges									(360,000,000)						(360,000,000)
Dividends to parent company									0
Transferred to the income statement									277,000,000						277,000,000
Other									(1,000,000)								(1,000,000)
Ending balance at Mar. 31, 2018	£ 22,740,000,000	£ 2,172,000,000		£ 8,000,000,000		£ 1,241,000,000		£ 11,327,000,000	£ 18,339,000,000		£ 2,172,000,000		£ 8,000,000,000		703,000,000		7,464,000,000
Statements [Line Items]
Transfer to realised profit															£ (83,000,000)		£ 83,000,000

[1] The allotted, called up, and fully paid ordinary share capital of the company at 31 March 2018 was £2,172m comprising 8,689,755,905 ordinary shares of 25p each.

[2] The share premium account, comprising the premium on allotment of shares, is not available for distribution.

[3] For further analysis of other reserves, see note 26.

[4] The allotted, called up and fully paid ordinary share capital of the company at 31 March 2018 and 31 March 2017 was £2,172m representing 8,689,755,905 ordinary shares of 25p each

[5] The share premium account, representing the premium on allotment of shares, and the capital redemption reserve are not available for distribution.

[6] A breakdown of other reserves is provided in note 14.

[7] As permitted by Section 408(3) of the Companies Act 2006, no income statement of the company is presented. The company’s profit for the financial year including dividends received from subsidiary undertakings was £2,057m (2016/17: £1,351m) before dividends paid of £nil (2016/17: £2,350m)

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Group plc statement of changes in equity (Parenthetical) - GBP (£)		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Statements [Line Items]
Ordinary shares		£ 2,172,000,000	£ 2,172,000,000	£ 2,172,000,000
Number of ordinary shares		8,689,755,905
Par value per share		£ 0.25
Total profit for the period including dividend income		£ 2,184,000,000	2,066,000,000	2,733,000,000
Dividends to shareholders			2,350,000,000	1,450,000,000
British Telecommunications plc [Member]
Statements [Line Items]
Ordinary shares		£ 2,172,000,000	£ 2,172,000,000
Number of ordinary shares		8,689,755,905	8,689,755,905
Par value per share		£ 0.25	£ 0.25
Total profit for the period including dividend income	[1]	£ 2,057,000,000	£ 1,351,000,000
Dividends to shareholders		£ 0	£ 2,350,000,000	£ 1,450,000,000

[1] As permitted by Section 408(3) of the Companies Act 2006, no income statement of the company is presented. The company’s profit for the financial year including dividends received from subsidiary undertakings was £2,057m (2016/17: £1,351m) before dividends paid of £nil (2016/17: £2,350m)

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Basis of preparation

12 Months Ended

Mar. 31, 2018

Basis Of Preparation [Abstract]

Basis of preparation

1. Basis of preparation

Preparationofthefinancialstatements

These consolidated financial statements have been prepared in accordance with the Companies Act 2006 as applicable to companies using International Financial Reporting Standards (IFRS), Article 4 of the IAS Regulation and International Accounting Standards (IAS) and IFRS and related interpretations, as adopted by the European Union. The consolidated financial statements are also in compliance with IFRS as issued by the International Accounting Standards Board (the IASB) and interpretations as issued by the IFRS Interpretations Committee. The consolidated financial statements are prepared on a going concern basis.

These financial statements consolidate British Telecommunications plc, the parent company, and its subsidiaries (together the ‘group’).

Theconsolidatedfinancial statementsare preparedon the historical costbasis,except forcertainfinancial andequity instrumentsthat have been measured atfairvalue.The consolidated financial statementsare presented inSterling,the functionalcurrency of British Telecommunications plc,the parent company.

New and amended accounting standards
effective during the year

Note 23 of these consolidated financial statements reflect the amendments of IAS 7 ‘Statement of Cash Flows’ requiring the disclosure of changes in liabilities arising from financing activities.

There have been no other new or amended standards or interpretations adopted during the year that have a significant impact on the financial statements.

New and amended accounting standards that
have been issued but are not yet effective

Thefollowingstandardshave been issued and are effectivefor accounting periodsending on or after1 April 2018 and are expectedtohave an impacton the group financial statements.

IFRS 15 ‘Revenue from Contracts with Customers’

Background

In May 2014, IFRS 15 ‘Revenue from Contracts with Customers’ was issued. It was subsequently amended in September 2015 and April 2016. It is effective for periods beginning on or after 1 January 2018. Transition to IFRS 15 for the group will take place on 1 April 2018. Results in the 2018/19 financial year will comply with IFRS 15, with the first Annual Report and Form 20-F published in accordance with IFRS 15 being that for the year ended 31 March 2019.

IFRS15 setsouttherequirementsforrecognising revenue and costsfrom contracts with customersand includes extensive disclosure requirements.Thestandardrequires entities to apportion revenue earned from contractstoindividual promises, or performance obligations, on a relative stand-aloneselling price basis, basedon a five-step model.

Transition

We previously disclosed in our Annual Report & Form 20-F 2017 that we were planning to adopt IFRS 15 retrospectively. This meant applying the new standard to each prior reporting period presented, ie 2016/17 and 2017/18, in accordance with IAS 8 ‘Accounting Policies, Changes in Accounting Estimates and Errors’.  Having considered further the factors that would influence our approach (including the time, effort and cost of adopting IFRS 15 retrospectively), as disclosed in the prior year Annual Report, we have decided to adopt the new standard on a modified retrospective basis and the group will recognise the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings at 1 April 2018, ie the date of initial application. Under this transition method:

–  the standard will be applied only to contracts in progress but not completed at the date of initial application

–  for contracts that were modified before 1 April 2018, the group shall reflect the aggregate effect of all of the modifications that occur before this date at 1 April 2018

–  we will not restate prior year comparatives for the effect of IFRS 15 but will instead restate our 1 April 2018 opening retained earnings for the full cumulative impact of adopting this standard

– for the year ended 31 March 2019 we will provide a reconciliation of our primary financial statements under IFRS 15 to those in accordance with IAS 18.

IFRS 15 Project

The group has deployed a cross-functional project team dedicated to the implementation of IFRS 15. This team has been engaged in determining accounting policies under the new standard, quantifying the transitional adjustments and selecting and implementing suitable systems solutions. The team is also reviewing the impact on tax, intragroup trading, forecasting, the bid and tender process and HR and remuneration plans. There is a significant impact on the group’s billing data and accounting platforms.

Performance obligations

IFRS 15 requires that at contract inception, we assess the goods or services promised in a contract with a customer and identify as a performance obligation each promise to transfer to the customer the good or service. Promises in a contract can be explicit, or implicit if the promises create a valid expectation to provide a good or service based on the customary business practices, published policies, or specific statements.

Thestand-aloneselling prices ofthegroup’s productsand services have been determined.Thesemay beregulatedprices,listprices, a cost-plusderived price,thepriceofsimilarproductswhensoldon astand-alonebasisby BTor acompetitor or in some casesthe contractpricewhere theprice contractedrepresentsa bespoke price that would be the same fora similar customerin a similar circumstance.

Financial Impact

Thegroup is in theprocessof finalising the impact of the standard including the final transition adjustment to retained earnings. We have estimated that the likely impact on transition at 1 April 2018 will produce a cumulative increase in retained earnings of between £1.1bn and £1.5bn before tax. The corresponding impact will

primarily be recorded as contract asset and will lead to an additional one-off cash tax payment split equally between 2018/19 and 2019/20. The cumulative increase in retained earnings is mainly due to the acceleration of handset revenues and, to a lesser extent, deferral of costs (notably third party contract acquisition costs primarily associated with post pay contracts).

The financial impact of each business area is as follows:

–  Under ourcurrent accounting policy,mobile handset revenue is recognised based on theamount thecustomerpays forthe handset when it is delivered tothe customer.Generallymobile handsets areeitherprovidedfor freeor fora small upfront charge.

Under IFRS15,additional revenue will be allocatedto themobile handsetatthestartof the contract.Thisis calculated with reference toits relative standalone value within the contract,regardless ofthe contract pricing. Foreach mobile handsetcontractthe revenue recognition profilewill change withgreaterdayone recognition ofrevenue forthe handset and a corresponding reduction inongoing mobile servicerevenue over the contractperiod. The difference between themobile handsetrevenue recognised and the amountscharged tothe customerwill be recognised as a contract asset.

Onadoption of IFRS15, we will recognise a contract asset for all open contracts at 1 April 2018.

Overtime, we expect the contractassetgenerated toremain at similarlevelsasold contractsexpire and new ones are signed. However,we will see short-termvolatility, forexample aroundkeyhandset launches.

This will be the most significant impact of the IFRS 15 adoption on the group and will primarily impact EE. To a lesser extent this will also impact mobile handset revenues in Business and Public Sector, in respect of the legacy EE business division, and BT Consumer. The impact in these customer-facing units is less significant due to the lower handset base.

Weexpect to see a similar trend in respect ofsubsidised equipment althoughwe expectthisto have a less significant impactdue tothelower relative standalone value forthis equipment.

–  Currently,salescommissions and otherthird partyacquisition costsresulting directly fromsecuring contractswith customers are expensed whenincurred.

Under IFRS15 salescommissions and otherthirdparty contractacquisition costswill berecognised as an asset,and amortised overthe period in which thecorresponding benefit is received, resulting in earlierprofitrecognition.

Theimpactis greatestin EEin respect ofthird-partyacquisition costs partiallyassociated withpost pay contracts.

–  The above two impacts will be partly offset by amended accounting for connections revenue. Currently,thegroup recognises connectionsrevenue upon performance of the connectionactivity.Under IFRS15 connections revenuewill be deferred and recognised on a straight-linebasisover the associated line/circuitcontractual period. This will mean thatrevenue and profitswill be recognised laterandon transition leads totherecognition of a contractliability as revenueand profitsare deferred tofuture periods. Wholesaleand Ventures and Openreach deliverthe majorityof thisservice and therefore will experience the majorityoftheimpact.Overtime,this liabilityis expected to remain atsimilar levels as old contractsexpire and new ones are signed.

Ontheadoption date we expectthe impact of this deferral to be significantly lessthanthe impact ofhandset revenue and thirdpartyacquisition costsnoted above.

–  We will provide for expected lifetime losses on recognised contract assets as required by IFRS 9 as set out below.

IFRS 15 will impact other areas but we do not expect the impact to be material. These include certain contract fulfilment costs which will be recognised as an asset and amortised over the period in which benefit is received and certain expenses will be recognised as a deduction from revenue.

IFRS 15 also provides more detailed guidance on how to account for contract modifications than the current revenue standards IAS 18 and IAS 11. Changes must be accounted for either as a retrospective change (creating either a catch up or deferral of previously recorded revenues), prospectively with a reallocation of revenues amongst identified performance obligations, or prospectively as separate contracts which will not require any reallocation. We expect contract modifications would primarily relate to changes in the agreed products and services to be provided to customers for long-term IT and networking solution contracts.

Disclosures

The adoption of IFRS 15 would also result in changes to our Annual Report disclosures. They key changes expected are as follows:

– we will amend our existing revenue disclosures to comply with the requirements to disaggregate revenue recognised from contracts with customers into categories that depict how the nature, amount, timing and uncertainty of revenue and associated cash flows are affected by economic factors

– we will provide further detail around contract balances and their movements

– we will provide an aggregate amount of the transaction price allocated to the performance obligation that are unsatisfied as of the end of the reporting period and an explanation of when the entity expects the amounts to be recognised as revenue.

IFRS 9 ‘Financial instruments’

IFRS9 is effectivefor BT from 1April 2018. Itis applicableto financial assetsand financial liabilitiesand covers the classification, measurement,impairment and de-recognition of financial assetsand liabilitiestogetherwitha new hedge accounting model.

Withtheexceptionoftheimpact on IFRS15 contractassetswe do not expectthestandard to have a materialimpacton our results, withthe keyissues forBTbeing arounddocumentationof policies, hedging strategyand new hedge documentation.

IFRS 9 operates an expected credit loss model rather than an incurred credit loss model. Providingforloss allowanceson ourexisting financial assetsis not expected tohave a material impact.We have included the impact of providing for losses on our contract assets within the estimated impact of the adoption of IFRS 15 as set out above.

IFRS 16 ‘Leases’

IFRS16 was published in January2016 and will be effective forBT from1 April 2019, replacing IAS17 ‘Leases’. We are planning to adopt IFRS 16 on a modified retrospective basis and the group will recognise the cumulative effect of initially applying the standard as an adjustment to the opening balance of retained earnings at 1 April 2019, ie the date of initial application. Results in the2019/20 financial year will be IFRS16 compliant and theAnnual Reportand 20-F 2020 will be the first to include the results on this basis.

The standard requires lessees to recognise assets and liabilities for all leases unless the lease term is 12 months or less, or the underlying asset is of low value.

The group is still in the process of quantifying the implications of this standard. However, we expect the following indicative impacts:

– thereis expected tobe an increase in totalassets,as leased assets which are currentlyaccountedfor offbalance sheet (ie classified asoperating leases under IAS17) will be recognised on balance sheet valued in accordance with the principles of IFRS 16.Thebiggest assetcategoryimpactedforthe group is expected tobe land and buildings

– thereis expected tobe an increase in debt,as liabilitiesrelating toexisting operating leases arerecognised. Theincrease in total debt will have an impacton gearing ratios

– operating lease expenditure will be reclassified and split between depreciation and finance costs. Therefore EBITDA will increase. Future depreciation and finance costs are also expected to increase as a result of increased assets and liabilities

– there is an expected temporary reduction in profit after tax as result of the above changes. This is expected to be driven by an increase in finance costs as a result of the new leases.  These finance costs will have an accelerated profile which will reduce once the leases are settled

– theremaybe a corresponding effecton taxbalances in relation toall oftheabove impacts.

This standard will require us to make key accounting judgements in particular around the likelihood of lease renewals.

Details of our existing operating lease commitments are set out in note 29.

Presentation of specific items

Ourincome statementand segmental analysis separatelyidentify tradingresultsbefore specific items.Thedirectors believe that presentation ofour resultsinthis wayisrelevant toan understanding ofour financial performance,as specific items are identifiedby virtue of theirsize,nature or incidence.This presentationis consistentwith theway thatfinancial performance ismeasured bymanagementand reportedto theBoard and the ExecutiveCommittee of BT Group plc and assists in providinga meaningful analysis ofourtrading results.In determining whetheran eventor transactionis specific,management considers quantitativeas well as qualitativefactorssuch asthe frequency or predictability ofoccurrence.

Furthermore,we consider a columnar presentation tobe appropriate,as itimproves theclarity ofthepresentation and is consistentwith the way thatfinancial performanceis measured by management and reported tothe Board and theExecutive Committee of BT Group plc.

Specificitemsmaynot be comparable tosimilarly titled measures used by other companies. Examples of chargesorcredits meeting theabove definition and which have been presentedas specificitemsin thecurrentand/orprioryears include acquisitions/disposals ofbusinesses and investments,regulatory settlements, historical insurance orlitigation claims,business restructuringprogrammes,assetimpairment charges, property rationalisation programmes,netintereston pensionsand the settlementofmultiple taxyears.Inthe event thatotheritems meetthecriteria,which are applied consistently fromyear to year,theyare also treatedas specific items.

Specificitemsforthe current and prior years are disclosed in note 8.

Annual Report & Form 20-F 2018 British Telecommunications PLC 1

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Critical accounting estimates and key judgements

12 Months Ended

Mar. 31, 2018

Critical Accounting Estimates And Key Judgements [Abstract]

Critical accounting estimates and key judgements

2. Critical accounting estimates

and key judgements

The preparation of financial statements in conformity with IFRS requires the use of accounting estimates and assumptions. It also requires management to exercise its judgement in the process of applying our accounting policies. We continually evaluate our estimates, assumptions and judgements based on available information and experience. As the use of estimates is inherent in financial reporting, actual results could differ from these estimates. Management has discussed its critical accounting estimates and associated disclosures with the Audit and Risk Committee of BT Group plc. The areas involving a higher degree of judgement or complexity are described in the applicable notes to the financial statements. Critical accounting estimates and key judgements can be identified throughout the notes by the following symbol.

We have the following critical accounting estimates (E) and key judgements (J):

– Revenue from multiple element arrangements, see note 4 (J).

– Subscriber acquisition and retention costs, see note 5 (J).

– Current and deferred income tax, see note 9 (E, J).

– Goodwill, see note 11 (E).

– Government grants relating to Broadband Delivery UK (BDUK) contracts, see note 12 (E, J).

– Long-term customer contracts, see note 16 (E).

– Provisions and contingent liabilities, see note 18 (E, J).

– Pension obligations, see note 19 (E, J).

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Significant accounting policies

12 Months Ended

Mar. 31, 2018

Significant Accounting Policies [Abstract]

Significant accounting policies

THE STRATEGIC REPORT GOVERNANCE FINANCIALSTATEMENTS ADDITIONAL INFORMATION

3. Significant accounting policies

The significant accounting policies applied in the preparation of our consolidated financial statements are set out below. These policies have been consistently applied to all the years presented, unless otherwise stated.

Basis of consolidation

The group financial statements consolidate the financial statements of British Telecommunications plc and its subsidiaries, and include its share of the results of associates and joint ventures using the equity method of accounting. The group recognises its direct rights to (and its share of) jointly held assets, liabilities, revenues and expenses of joint operations under the appropriate headings in the consolidated financial statements.

A subsidiary is an entity that is controlled by another entity, known as the parent or investor. An investor controls an investee when the investor is exposed, or has rights, to variable returns from its involvement with the investee and has the ability to affect those returns through its power over the investee.

Non-controlling interests in the net assets of consolidated subsidiaries, which consist of the amounts of those interests at the date of the original business combination and non-controlling share of changes in equity since the date of the combination, are not material to the group’s financial statements.

The results of subsidiaries acquired or disposed of during the year are consolidated from and up to the date of change of control. Where necessary, accounting policies of subsidiaries have been aligned with the policies adopted by the group. All intra-group transactions including any gains or losses, balances, income or expenses are eliminated in full on consolidation.

When the group loses control of a subsidiary, the profit or loss on disposal is calculated as the difference between (i) the aggregate of the fair value of the consideration received and the fair value of any retained interest and (ii) the previous carrying amount of the assets (including goodwill), and liabilities of the subsidiary and any non-controlling  interests. The profit or loss on disposal is recognised as a specific item.

Revenue

Revenue represents the fair value of the consideration received or receivable for communications services and equipment sales, net of discounts and sales taxes. Revenue is recognised when it is probable that the economic benefits associated with a transaction will flow to the group and the amount of revenue and associated costs can be measured reliably. The accounting for revenue sharing arrangements depends on the analysis of the facts and circumstances surrounding these transactions.

Where we act as an agent in a transaction, we recognise revenue net of directly attributable costs.

Services

Revenue arising from separable installation and connection services is recognised when it is earned, upon activation. Revenue from the rental of analogue and digital lines and private circuits as well as wholesale access revenue is recognised on a straight line basis over the period to which it relates. Revenue from calls is recognised at the time the call is made over our network. Subscription fees, consisting primarily of monthly charges for access to broadband and other internet access or voice services, are recognised as revenue as the service is provided. Revenue from the interconnection of voice and data traffic between other telecommunications operators is recognised at the time of transit across our network.

Equipment sales

Revenue from the sale of equipment is recognised when all the significant risks and rewards of ownership are transferred to the customer, which is normally the date the equipment is delivered and accepted by the customer.

Long-term contractual arrangements

Revenue from long-term contractual arrangements, including fixed price contracts to design and build software solutions, is recognised based on the percentage of completion method. The stage of completion is estimated using an appropriate measure according to the nature of the contract such as the proportion of costs incurred relative to the estimated total contract costs, or other measures of completion such as the achievement of contract milestones and customer acceptance. In the case of time and materials contracts, revenue is recognised as the service is rendered.

Costs related to delivering services under long-term contractual arrangements are expensed as incurred except for an element of costs incurred in the initial contract set-up, transition or transformation phase, which is deferred and recorded within non-current assets. These costs are then recognised in the income statement on a straight line basis over the remaining contract term, unless the pattern of service delivery indicates a different profile is more appropriate. These costs are directly attributable to specific contracts, relate to future activity, will generate future economic benefits and are assessed for recoverability on a regular basis.

The percentage of completion method relies on estimates of total expected contract revenues and costs, as well as reliable measurement of the progress made towards completion. Unless the financial outcome of a contract can be estimated with reasonable certainty, no attributable profit is recognised. In such circumstances, revenue is recognised equal to the costs incurred to date, to the extent that such revenue is expected to be recoverable, or costs are accrued to bring the margin to nil. Recognised revenue and profits are subject to revisions during the contract if the assumptions regarding the overall contract outcome are changed. The cumulative impact of a revision in estimates is recorded in the period in which such revisions become likely and can be estimated. Where the actual and estimated costs to completion exceed the estimated revenue for a contract, the full contract life loss is recognised immediately.

Multiple element arrangements and bundles

Revenue from multiple element arrangements and bundles is described in note 4.

Operating and reportable segments

Our operating segments are reported based on financial information provided to the Executive Committee of BT Group plc which is the key management committee and represents the ‘chief operating decision maker’.

Our organisational structure reflects the different customer groups to which we provide communications products and services via our customer-facing units: BT Consumer, EE, Business and Public Sector, Global Services, Wholesale and Ventures and Openreach. The customer-facing units are supported by an internal service unit: Technology, Service & Operations (TSO).

The customer-facing units are our reportable segments and generate substantially all of our revenue. We aggregate the remaining operations and include within the ‘Other’ category to reconcile to the consolidated results of the group. The ‘Other’ category includes TSO and our corporate units including procurement and property management.

Provisions for the settlement of significant legal, commercial and regulatory disputes, which are negotiated at a group level, are initially recorded in the ‘Other’ segment. On resolution of the dispute, the full impact is recognised in the results of the relevant customer-facing unit and offset in the group results through the utilisation of the provision previously charged to the ‘Other’ segment. Settlements which are particularly significant or cover more than one financial year may fall within the definition of specific items as detailed on page 209.

The costs incurred by TSO are recharged to the customer-facing units to reflect the services it provides to them. Depreciation and amortisation incurred by TSO in relation to the networks and systems it manages and operates on behalf of the customer-facing units is allocated to the customer-facing units based on their respective utilisation. Capital expenditure incurred by TSO for specific projects undertaken on behalf of the customer-facing units is allocated based on the value of the directly attributable expenditure incurred. Where projects are not directly attributable to a particular customer-facing unit, capital expenditure is allocated between them based on the proportion of estimated future economic benefits. TSO and the group’s corporate functions are not reportable segments as they did not meet the quantitative thresholds as set out in IFRS 8 ‘Operating Segments’ for any of the years presented.

Performance of each reportable segment is measured based on adjusted EBITDA, defined as EBITDA before specific items, as included in the internal financial reports reviewed by the Executive Committee of BT Group plc. EBITDA is defined as the operating profit or loss before depreciation, amortisation, net finance expense and taxation. Adjusted EBITDA is considered to be a useful measure of the operating performance of the customer-facing units because it approximates the underlying operating cash flow by eliminating depreciation and amortisation and also provides a meaningful analysis of trading performance by excluding specific items, which are disclosed separately by virtue of their size, nature or incidence. Specific items are detailed in note 8 and are not allocated to the reportable segments as this reflects how they are reported to the Executive Committee of BT Group plc. Finance expense and income are not allocated to the reportable segments, as the central treasury function manages this activity, together with the overall net debt position of the group.

On 1 April 2018, our BT Consumer and EE customer-facing units were brought together to drive converged products and accelerate transformation. Additionally, Business and Public Sector and Wholesale and Ventures will be brought together from 1 October 2018. Each of these businesses operated separately throughout 2017/18 and therefore have been presented as four separate operating segments throughout these financial statements, unless explicitly stated otherwise. For further information see note 30.

Retirement benefits

The group’s net obligation in respect of defined benefit pension plans is the present value of the defined benefit obligation less the fair value of the plan assets.

The calculation of the obligation is performed by a qualified actuary using the projected unit credit method and key actuarial assumptions at the balance sheet date.

The income statement expense is allocated between an operating charge and net finance income or expense. The operating charge reflects the increase in the defined benefit obligation resulting from the pension benefit earned by active employees in the current period, the costs of administering the plans and any past service costs/credits such as those arising from curtailments or settlements. The net finance income or expense reflects the interest on the net retirement benefit obligations recognised in the group balance sheet, based on the discount rate at the start of the year. Actuarial gains and losses are recognised in full in the period in which they occur and are presented in the group statement of comprehensive income.

The group also operates defined contribution pension plans and the income statement expense represents the contributions payable for the year.

Property, plant and equipment

Property, plant and equipment are included at historical cost, net of accumulated depreciation, government grants and any impairment charges. Property, plant and equipment acquired through business combinations are initially recorded at fair value and subsequently accounted for on the same basis as the group’s existing assets. An item of property, plant and equipment is derecognised on disposal or when no future economic benefits are expected to arise from the continued use of the asset. The difference between the sale proceeds and the net book value at the date of disposal is recognised in operating costs in the income statement.

Included within the cost of network infrastructure and equipment are direct and indirect labour costs, materials and directly attributable overheads.

Depreciation is provided on property, plant and equipment on a straight line basis from the time the asset is available for use, to write off the asset’s cost over the estimated useful life taking into account any expected residual value. Freehold land is not depreciated.

The estimated useful lives assigned to principal categories of assets are as follows:

Land and buildings
–  Freehold buildings	14 to 50 years
–  Short-term leasehold improvements				Shorter of 10 years or lease term
–  Leasehold land and buildings		Unexpired portion of lease or 40 years, whichever is the shorter
Network infrastructure
Transmission equipment
–  Duct		40 years
–  Cable		3 to 25 years
–  Fibre		5 to 20 years
Exchange equipment		2 to 13 years
Other network equipment		2 to 20 years
Other assets
–  Motor vehicles		2 to 9 years
–  Computers and office equipment			3 to 7 years

Assets held under finance leases are depreciated over the shorter of the lease term or their useful economic life. Residual values and useful lives are reassessed annually and, if necessary, changes are recognised prospectively.

Network share assets

Certain assets have been contributed to a network share arrangement by both EE and Hutchison 3G UK Limited, with legal title remaining with the contributor. This is considered to be a reciprocal arrangement. The group’s share of the assets on acquisition of EE was recognised at fair value within tangible assets, and depreciated in line with the group’s policy. Subsequent additions are recorded at cost. For further information see note 12.

Intangible assets

Identifiable intangible assets are recognised when the group controls the asset, it is probable that future economic benefits attributable to the asset will flow to the group and the cost of the asset can be reliably measured. All intangible assets, other than goodwill, are amortised over their useful economic life. The method of amortisation reflects the pattern in which the assets are expected to be consumed. If the pattern cannot be determined reliably, the straight line method is used.

Goodwill

Goodwill represents the excess of the cost of an acquisition over the fair value of the group’s share of the identifiable net assets (including intangible assets) of the acquired business.

For the purpose of impairment testing, goodwill acquired in a business combination is allocated to each of the Cash Generating Units (CGUs) that is expected to benefit from the business combination. Each CGU to which goodwill is allocated represents the lowest level within the group at which the goodwill is monitored for internal management purposes.

Acquired intangible assets – customer relationships and brands

Intangible assets such as customer relationships or brands acquired through business combinations are recorded at fair value at the date of acquisition and subsequently carried at amortised cost. Assumptions are used in estimating the fair values of these relationships or brands and include management’s estimates of revenue and profits to be generated by them.

Telecommunications licences

Licence fees paid to governments, which permit telecommunications activities to be operated for defined periods, are initially recorded at cost and amortised from the time the network is available for use to the end of the licence period or where our usage can extend beyond the initial licence period, over the period we expect to benefit from the use of the licences, which is typically 20 years. Licences acquired through business combinations are recorded at fair value at the date of acquisition and subsequently carried at amortised cost. The fair value is based on management’s assumption of future cash flows using market expectations at acquisition date.

Computer software

Computer software comprises computer software licences purchased from third parties, and also the cost of internally developed software. Computer software licences purchased from third parties are initially recorded at cost.

Costs directly associated with the production of internally developed software, including direct and indirect labour costs of development, are capitalised only where it is probable that the software will generate future economic benefits, the cost of the asset can be reliably measured and technical feasibility can be demonstrated, in which case it is capitalised as an intangible asset on the balance sheet. Costs which do not meet these criteria and research costs are expensed as incurred.

The group’s development costs which give rise to internally developed software include upgrading the network architecture or functionality and developing service platforms aimed at offering new services to the group’s customers. See research and development on page 17.

Other

Other intangible assets include website development costs and other licences. Items are capitalised at cost and amortised on a straight line basis over their useful economic life or the term of the contract.

Estimated useful economic lives

The estimated useful economic lives assigned to the principal categories of intangible assets are as follows:

–  Computersoftware	2to10years
–  Telecommunicationslicences	2to20years
–  Customerrelationshipsandbrands	1to15years

Programme rights

Programme rights are recognised on the balance sheet from the point at which the legally enforceable licence period begins. Rights for which the licence period has not started are disclosed as contractual commitments in note 29. Payments made to receive commissioned or acquired programming in advance of the legal right to broadcast the programmes are classified as prepayments.

Programmes produced internally are charged to the income statement over the period of the related broadcast.

Programme rights are tested for impairment in accordance with the group’s policy for impairment of non-financial assets set out below. Related cash outflows are classified as operating cash flows in the cash flow statement.

Inventories

Network maintenance equipment and equipment to be sold to customers are stated at the lower of cost or net realisable value, taking into account expected revenues from the sale of packages comprising a mobile handset and a subscription. Cost corresponds to purchase or production cost determined by either the first in first out (FIFO) or average cost method.

Provisions

Provisions are recognised when the group has a present legal or constructive obligation as a result of past events, it is probable that an outflow of resources will be required to settle the obligation and the amount can be reliably estimated. Provisions are determined by discounting the expected future cash flows at a pre-tax rate that reflects current market assessments of the time value of money and the risks specific to the liability. Financial liabilities within provisions are initially recognised at fair value and subsequently carried at amortised cost using the effective interest method. Onerous lease provisions are measured at the lower of the cost to fulfil or to exit the contract.

Current and deferred income tax

Current income tax is calculated on the basis of the tax laws enacted or substantively enacted at the balance sheet date in the countries where the group’s subsidiaries, associates and joint ventures operate and generate taxable income. The group periodically evaluates positions taken in tax returns with respect to situations in which applicable tax regulation is subject to interpretation, and the group establishes provisions where appropriate on the basis of the amounts expected to be paid to tax authorities.

Deferred tax is recognised, using the liability method, in respect of temporary differences between the carrying amount of the group’s assets and liabilities and their tax base. Deferred income tax assets and liabilities are offset when there is a legally enforceable right to offset current tax assets against current tax liabilities and when the deferred income tax assets and liabilities relate to income taxes levied by the same taxation authority on either the taxable entity or different taxable entities where there is an intention to settle the balances on a net basis. Any remaining deferred tax asset is recognised only when, on the basis of all available evidence, it can be regarded as probable that there will be suitable taxable profits, within the same jurisdiction, in the foreseeable future against which the deductible temporary difference can be utilised.

Deferred tax is determined using tax rates that are expected to apply in the periods in which the asset is realised or liability settled, based on tax rates and laws that have been enacted or substantively enacted by the balance sheet date.

Impairment of non-financial assets

Intangible assets with finite useful lives and property, plant and equipment are tested for impairment if events or changes in circumstances (assessed at each reporting date) indicate that the carrying amount may not be recoverable. When an impairment test is performed, the recoverable amount is assessed by reference to the higher of the net present value of the expected future cash flows (value in use) of the relevant cash generating unit and the fair value less costs to dispose.

Goodwill is reviewed for impairment at least annually. Impairment losses are recognised in the income statement, as a specific item. If a cash generating unit is impaired, impairment losses are allocated firstly against goodwill, and secondly on a pro-rata basis against intangible and other assets.

Government grants

Government grants are recognised when there is reasonable assurance that the conditions associated with the grants have been complied with and the grants will be received.

Grants for the purchase or production of property, plant and equipment are deducted from the cost of the related assets and reduce future depreciation expense accordingly. Grants for the reimbursement of operating expenditure are deducted from the related category of costs in the income statement. Government grants received relating to the BDUK programme and other rural superfast broadband contracts are accounted for as described under ‘Critical accounting estimates and key judgements’.

Once a government grant is recognised, any related deferred income is treated in accordance with IAS 20 ‘Accounting for Government Grants and Disclosure of Government Assistance’.

Foreign currencies

Foreign currency transactions are translated into the functional currency using the exchange rates prevailing at the date of the transaction. Foreign exchange gains and losses resulting from the settlement of transactions and the translation of monetary assets and liabilities denominated in foreign currencies at period end exchange rates are recognised in the income statement line which most appropriately reflects the nature of the item or transaction.

On consolidation, assets and liabilities of foreign undertakings are translated into Sterling at year end exchange rates. The results of foreign undertakings are translated into Sterling at average rates of exchange for the year (unless this average is not a reasonable approximation of the cumulative effects of the rates prevailing on the transaction dates, in which case income and expenses are translated at the dates of the transactions). Foreign exchange differences arising on the retranslation of foreign undertakings are recognised directly in a separate component of equity, the translation reserve.

In the event of the disposal of an undertaking with assets and liabilities denominated in a foreign currency, the cumulative translation difference associated with the undertaking in the translation reserve is charged or credited to the gain or loss on disposal recognised in the income statement.

Research and development

Research expenditure is recognised in the income statement in the period in which it is incurred. Development expenditure, including the cost of internally developed software, is recognised in the income statement in the period in which it is incurred unless it is probable that economic benefits will flow to the group from the asset being developed, the cost of the asset can be reliably measured and technical feasibility can be demonstrated, in which case it is capitalised as an intangible asset on the balance sheet. Capitalisation ceases when the asset being developed is ready for use. Research and development costs include direct and indirect labour, materials and directly attributable overheads.

Leases

The determination of whether an arrangement is, or contains, a lease is based on the substance of the arrangement and requires an assessment of whether the fulfilment of the arrangement is dependent on the use of a specific asset or assets and whether the arrangement conveys the right to use the asset.

Leases of property, plant and equipment where the group holds substantially all the risks and rewards of ownership are classified as finance leases. Finance lease assets are capitalised at the commencement of the lease term at the lower of the present value of the minimum lease payments or the fair value of the leased asset. The obligations relating to finance leases, net of finance charges in respect of future periods, are recognised as liabilities. Leases are subsequently measured at amortised cost using the effective interest method.

Leases where a significant portion of the risks and rewards are held by the lessor are classified as operating leases. Rentals are charged to the income statement on a straight line basis over the period of the lease.

Share-based payments

BT Group plc operates a number of equity settled share-based payment arrangements, under which the group receives services from employees in consideration for equity instruments (share options and shares) of BT Group plc. Equity settled share-based payments are measured at fair value at the date of grant. Market-based performance criteria and non-vesting conditions (for example, the requirement for employees to make contributions to the share purchase programme) are reflected in this measurement of fair value. The fair value determined at the grant date is recognised as an expense on a straight line basis over the vesting period, based on the group’s estimate of the options or shares that will eventually vest and adjusted for the effect of non market-based vesting conditions. Fair value is measured using either the Binomial options pricing model or Monte Carlo simulations, whichever is more appropriate to the share-based payment arrangement.

Service and performance conditions are vesting conditions. Any other conditions are non-vesting conditions which have to be taken into account to determine the fair value of equity instruments granted. In the case that an award or option does not vest as a result of a failure to meet a non-vesting condition that is within the control of either counterparty, this is accounted for as a cancellation. Cancellations are treated as accelerated vesting and all remaining future charges are immediately recognised in the income statement. As the requirement to save under an employee saveshare arrangement is a non-vesting condition, employee cancellations, other than through a termination of service, are treated as an accelerated vesting.

No adjustment is made to total equity for awards that lapse or are forfeited after the vesting date.

Termination benefits

Termination benefits (leaver costs) are payable when employment is terminated before the normal retirement date, or when an employee accepts voluntary redundancy in exchange for these benefits. The group recognises termination benefits when it is demonstrably committed to the affected employees leaving the group.

Financial instruments

Financial liabilities at amortised cost

Trade and other payables

Financial liabilities within trade and other payables are initially recognised at fair value, which is usually the original invoiced amount, and subsequently carried at amortised cost using the effective interest method.

Loans and other borrowings

Loans and other borrowings are initially recognised at the fair value of amounts received net of transaction costs. Loans and other borrowings are subsequently measured at amortised cost using the effective interest method and, if included in a fair value hedge relationship, are re-valued to reflect the fair value movements on the hedged risk associated with the loans and other borrowings. The resulting amortisation of fair value movements, on de-designation of the hedge, is recognised in the income statement.

Available-for-sale investments

Liquid and other investments are classified as available-for-sale investments and are initially recognised at fair value plus direct transaction costs. These are re-measured at subsequent reporting dates to fair value, with unrealised gains and losses (except for changes in exchange rates for monetary items, interest, dividends and impairment losses, which are recognised in the income statement) recognised in equity. When the financial asset is derecognised, at which time the cumulative gain or loss previously recognised in equity is taken to the income statement, in the line that most appropriately reflects the nature of the item or transaction. On disposal or impairment of the investments, any gains and losses that have been deferred in other comprehensive income are re-classified to the income statement. Dividends on equity investments are recognised in the income statement when the group’s right to receive payment is established. Equity investments are recorded in non-current assets unless they are expected to be sold within one year.

Loans and receivables

Trade and other receivables

Trade and other receivables are initially recognised at fair value, which is usually the original invoiced amount, and are subsequently carried at amortised cost, using the effective interest method, less provisions made for doubtful receivables. Provisions are made specifically where there is evidence of a risk of non-payment, taking into account ageing, previous losses experienced and general economic conditions.

Cash and cash equivalents

Cash and cash equivalents comprise cash in hand and current balances with banks and similar institutions, which are readily convertible to cash and are subject to insignificant risk of changes in value and have an original maturity of three months or less. For the purpose of the consolidated cash flow statement, cash and cash equivalents are as defined above net of outstanding bank overdrafts. Bank overdrafts are included within loans and other borrowings, in current liabilities on the balance sheet.

Financial assets and liabilities at fair value through profit or loss

All of the group’s derivative financial instruments are held for trading and classified as fair value through profit or loss.

Derivative financial instruments

The group uses derivative financial instruments mainly to reduce exposure to foreign exchange and interest rate risks. The group’s policy is not to use derivatives for trading purposes. However, derivatives that do not qualify for hedge accounting or are specifically not designated as a hedge where natural offset is more appropriate are initially recognised and subsequently measured at fair value through profit and loss. Any direct transaction costs are recognised immediately in the income statement. Gains and losses on re-measurement are recognised in the income statement in the line that most appropriately reflects the nature of the item or transaction to which they relate. Derivative financial instruments are classified as current assets or current liabilities where they have a maturity period within 12 months. Where derivative financial instruments have a maturity period greater than 12 months, they are classified within either non-current assets or non-current liabilities.

Where the fair value of a derivative contract at initial recognition is not supported by observable market data and differs from the transaction price, a day one gain or loss will arise which is not recognised in the income statement. Such gains and losses are deferred and amortised to the income statement based on the remaining contractual term and as observable market data becomes available.

Hedge accounting

Where derivatives qualify for hedge accounting, recognition of any resultant gain or loss depends on the nature of the hedge. To qualify for hedge accounting, hedge documentation must be prepared at inception and the hedge must be expected to be highly effective both prospectively and retrospectively. The hedge is tested for effectiveness at inception and in subsequent periods in which the hedge remains in operation. Hedge accounting is discontinued when the hedging instrument expires, or is sold, terminated or no longer qualifies for hedge accounting or the group chooses to end the hedge relationship. The group designates certain derivatives as either cash flow hedges or fair value hedges.

Cash flow hedges

When a derivative financial instrument is designated as a hedge of the variability in cash flows of a recognised asset or liability, or a highly probable transaction, the effective part of any gain or loss on the derivative financial instrument is recognised directly in equity, in the cash flow reserve. For cash flow hedges of recognised assets or liabilities, the associated cumulative gain or loss is removed from equity and recognised in the same line of the income statement and in the same period or periods that the hedged transaction affects the income statement. Any ineffectiveness arising on a cash flow hedge of a recognised asset or liability is recognised immediately in the same income statement line as the hedged item. Where ineffectiveness arises on highly probable transactions, it is recognised in the income statement line which most appropriately reflects the nature of the item or transaction.

Fair value hedges

When a derivative financial instrument is designated as a hedge of the variability in fair value of a recognised asset or liability, or unrecognised firm commitment, the change in fair value of the derivative that is designated as a fair value hedge is recorded in the income statement at each reporting date, together with any changes in fair value of the hedged asset or liability that is attributable to the hedged risk.

British Telecommunications plc Annual Report & Form 20-F 2018 1

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Segment information

12 Months Ended

Mar. 31, 2018

Disclosure Of Operating Segments [Abstract]

Segment information

4. Segment information

The definition of our operating and reportable segments is provided on pages 114 and 115. We have set out below information regarding the results of each reportable segment.

Segment revenueandprofit

Year ended 31 March 2018	BT Consumer £m			EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		5,066			5,294			4,563			5,013			2,009			5,123			8			27,076
Internal revenue		(66	)		(37	)		(115	)		–			(134	)		(2,978	)		–			(3,330	)
Revenue from external customersa		5,000			5,257			4,448			5,013			1,875			2,145			8			23,746
EBITDAb		1,023			1,353			1,418			434			754			2,520			6			7,508
Depreciation and amortisation		(216	)		(776	)		(365	)		(424	)		(311	)		(1,360	)		(62	)		(3,514	)
Operating profit (loss)a		807			577			1,053			10			443			1,160			(56	)		3,994
Specific items (note 8)																							(610	)
Operating profit																							3,384
Net finance expensec																							(579	)
Share of post tax profit (loss) of associates and joint ventures																							(1	)
Profit before tax																							2,804

Year ended 31 March 2017	BT Consumer £m			EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		4,934			5,090			4,758			5,479			2,109			5,098			10			27,478
Internal revenue		(63	)		(37	)		(122	)		–			(138	)		(3,036	)		–			(3,396	)
Revenue from external customersa		4,871			5,053			4,636			5,479			1,971			2,062			10			24,082
EBITDAb		1,012			1,156			1,528			495			834			2,633			(10	)		7,648
Depreciation and amortisation		(209	)		(780	)		(352	)		(439	)		(306	)		(1,369	)		(55	)		(3,510	)
Operating profit (loss)a		803			376			1,176			56			528			1,264			(65	)		4,138
Specific items (note 8)																							(968	)
Operating profit																							3,170
Net finance expensec																							(610	)
Share of post tax profit (loss) of associates and joint ventures																							(9	)
Profit before tax																							2,551

Year ended 31 March 2016	BT Consumer £m			EE £m		d	Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		4,608			841			4,294			5,074			2,274			5,100			11			22,202
Internal revenue		(65	)		(7	)		(99	)		–			(94	)		(3,058	)		–			(3,323	)
Revenue from external customersa		4,543			834			4,195			5,074			2,180			2,042			11			18,879
EBITDAb		1,055			173			1,414			479			755			2,659			(77	)		6,458
Depreciation and amortisation		(207	)		(146	)		(284	)		(422	)		(253	)		(1,301	)		(18	)		(2,631	)
Operating profit (loss)a		848			27			1,130			57			502			1,358			(95	)		3,827
Specific items (note 8)																							(212	)
Operating profit																							3,615
Net finance expensec																							(380	)
Share of post tax profit (loss) of associates and joint ventures																							6
Profit before tax																							3,241

^a Before specific items.

^b EBITDA is stated before specific items and is the group’s profitability measure for segments.

^c Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m). See note 8.

^d EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

What are our internal revenue and costs?

Most of our internal trading relates to Openreach and arises on rentals, and any associated connection or migration charges, of the UK access lines and other network products to the customer-facing units. This occurs both directly, and also indirectly, through TSO which is included within the ‘Other’ segment. Wholesale and Ventures internal revenue arises from EE for mobile ethernet access and TSO for transmission planning services. Internal revenue in Business and Public Sector relates primarily to the use of BT Ireland’s network by other customer-facing units. Internal revenue arising in BT Consumer relates primarily to employee broadband and wi-fi services.

Intra-group revenue generated from the sale of regulated products and services is based on market price. Intra-group revenue from the sale of other products and services is agreed between the relevant customer-facing units and therefore customer-facing units profitability may be impacted by transfer pricing levels.

The tables below show internal revenue and costs recorded by each reportable segment.

	Internal cost recorded by
Year ended 31 March 2018	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–		24		20		4		–		18		66
EE		–		–		–		–		37		–		–		37
Business and Public Sector		62		2		–		32		19		–		–		115
Global Services		–		–		–		–		–		–		–		–
Wholesale and Ventures		1		2		13		10		–		42		66		134
Openreach		896		–		210		125		232		–		1,515		2,978
Total		959		4		247		187		292		42		1,599		3,330

	Internal cost recorded by
Year ended 31 March 2017	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–	21		20		4			–	18		63
EE		–		–		–		–		37		–		–		37
Business and Public Sector		60		3		–		39		20		–		–		122
Global Services		–		–		–		–		–		–		–		–
Wholesale and Ventures		–		–		2		23		–		39		74		138
Openreach		910		–		236		158		260		–		1,472		3,036
Total		970		3		259		240		321		39		1,564		3,396

	Internal cost recorded by
Year ended 31 March 2016	BT Consumer £m		EE £m		a	Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–			20		23		4		–		18		65
EEa		–		–			–		–		7		–		–		7
Business and Public Sector		60		1			–		18		19		1		–		99
Global Services		–		–			–		–		–		–		–		–
Wholesale and Ventures		–		12			5		22		–		55		–		94
Openreach		905		–			262		173		264		–		1,454		3,058
Total		965		13			287		236		294		56		1,472		3,323

^a EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Revenue by products and services

What critical accounting judgements do we make when we have revenue from multiple element arrangements?

Where a contractual arrangement consists of two or more separate elements that have value to a customer on a standalone basis, revenue is recognised for each element as if it were an individual contract. Total contract consideration is allocated between the separate elements based on their fair value. We apply judgement in both identifying separate elements and allocating consideration between them.

Sales of bundled offers in our mobile businesses frequently include a handset and a telecommunications service contract. There is objective and reliable evidence of fair value for the telecommunications service to be delivered and this represents the revenue recognised in respect of the services delivered. The residual value of the bundled offer therefore represents the revenue in respect of the handset. Revenue allocated to the deliverables is restricted to the amount that is receivable without the delivery of additional goods or services.

For offers that cannot be separated into identifiable elements, revenues are recognised in full over the life of the contract. The main example is connection to a service where this does not represent a separately identifiable transaction from the subscription.

Year ended 31 March	2018 £m		2017 £m		2016 £m
ICT and managed networks		5,530		5,927		6,193
Broadband and TV		4,655		4,477		3,535
Mobile		6,451		6,358		1,326
Calls, lines and connections		5,126		5,069		5,920
Transit		265	404		419
Other products and services		1,719		1,847		1,486
Revenuea		23,746		24,082		18,879

^a Before specific items.

Capital expenditure

Year ended 31 March 2018	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Intangible assets		106		130		93		92		87		70		64		642
Property, plant and equipment		185		498		211		186		142		1,588		70		2,880
Capital expenditurea		291		628		304		278		229		1,658		134		3,522

Year ended 31 March 2017	BT Consumer £m	EE £m	Business and Public Sector £m	Global Services £m	Wholesale and Ventures £m	Openreach £m		Other £m	Total £m
Intangible assets	92	133	64	126	77	74		55	621
Property, plant and equipment	145	483	211	235	149		1,499	111		2,833
Capital expenditurea	237	616	275	361	226		1,573	166		3,454

Year ended 31 March 2016	BT Consumer £m	EE £m	b	Business and Public Sector £m	Global Services £m	Wholesale and Ventures £m	Openreach £m		Other £m	Total £m
Intangible assets	88	29		36	62	70	62		65	412
Property, plant and equipment	119	67		117	293	139		1,385	90		2,210
Capital expenditurea	207	96		153	355	209		1,447	155		2,622

^a Net of government grants.

^b EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

How do we determine our geographic information?

The UK is our country of domicile and we generate the majority of our revenue from external customers in the UK. The geographic analysis of revenue is based on the country of origin in which the customer is invoiced. The geographic analysis of non-current assets, which exclude derivative financial instruments, investments and deferred tax assets, is based on the location of the assets.

Revenue from external customers

Year ended 31 March	2018 £m		2017 £m		2016 £m
UK		19,687		19,421		14,814
Europe, Middle East and Africa, excluding the UK		2,489		2,841		2,442
Americas		996		1,148		1,011
Asia Pacific		574		672		612
Revenuea		23,746		24,082		18,879

^a Before specific items.

Non-current assets

At 31 March	2018 £m		2017 £m		2016 £m
UK		28,843		28,818		28,583
Europe, Middle East and Africa, excluding the UK		2,527		2,535		2,349
Americas		331		424		548
Asia Pacific		109		149		191
Non-current assets		31,810		31,926		31,671

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Operating Costs

12 Months Ended

Mar. 31, 2018

Operating Costs [Abstract]

Operating costs

5. Operating costs

Year ended 31 March	Notes	2018 £m			2017 £m			2016 £m
Operating costs by nature
Staff costs:
Wages and salaries			4,223			4,128			3,684
Social security costs			461			477			398
Other pension costs	19		624			521			494
Share-based payment expense	20		84			57			58
Total staff costs			5,392			5,183			4,634
Own work capitalised			(798	)		(813	)		(720	)
Net staff costs			4,594			4,370			3,914
Net indirect labour costsa			315			399			304
Net labour costs			4,909			4,769			4,218
Payments to telecommunications operators			2,306			2,653			2,183
Property and energy costs			1,285			1,202			1,024
Network operating and IT costs			963			983			644
TV programme rights charges			763			714			544
Other operating costs			6,234			6,298			4,023
Other operating income			(222	)		(185	)		(215	)
Depreciation of property, plant and equipment
Owned assets	12		2,381			2,382			2,000
Held under finance leases	12		10			10			10
Amortisation of intangible assetsb	11		1,123			1,118			621
Total operating costs before specific items			19,752			19,944			15,052
Specific items	8		587			948			345
Total operating costs			20,339			20,892			15,397
Operating costs before specific items include the following:
Leaver costsc			50			86			109
Research and development expenditured			632			638			574
Operating lease charges			732			692			441
Foreign currency gains			–			(12	)		(1	)
Government grants			(3	)		(5	)		(6	)

^a Net of capitalised indirect labour costs of £612m (2016/17: £463m, 2015/16: £430m).

^b Excludes £nil (2016/17: £62m, 2015/16: £nil) of amortisation presented as specific items which relate to a write off of software costs as a result of the integration of EE. Refer to note 8.

^c Leaver costs are included within wages and salaries, except for leaver costs of £168m (2016/17: £37m, 2015/16: £nil) associated with restructuring and EE integration costs, which have been recorded as specific items.

^d Research and development expenditure reported in the income statement, includes amortisation of £573m (2016/17: £577m, 2015/16: £501m) in respect of internally developed computer software and operating expenses of £59m (2016/17: £61m, 2015/16: £73m). In addition, the group capitalised software development costs of £450m (2016/17: £457m, 2015/16: £399m).

Why is the treatment of our subscriber acquisition and retention costs a critical judgement?

Subscriber acquisition and retention costs are recognised as an expense within other operating costs for the period in which they are incurred. If subscriber acquisition and retention costs are paid in advance they are recognised as prepayments provided the amounts are able to be measured reliably and are expected to be recoverable. In some cases, contractual clauses with retailers provide for profit-sharing based on the recognised and paid revenue. In these cases we recognise an expense when the revenue is earned from the customer and a corresponding liability to pay that retailer. In some cases we need to exercise judgement in assessing whether we have an upfront obligation based on the contractual terms.

Who are our key management personnel and how are they compensated?

Key management personnel comprise executive and non-executive directors and members of the BT Group plc Executive Committee as well as the directors of the company. It is the BT Group plc Executive Committee which has responsibility for planning, directing and controlling the activities of the group.

Compensation of key management personnel is shown in the table below:

Year ended 31 March	2018 £m		2017 £m		2016 £m
Short-term employee benefits	12.4			10.9		10.3
Post employment benefits	1.4			1.4		1.2
Share-based payments	6.6			5.8		5.9
Termination benefits		2.2		–		0.6
	22.6			18.1		18.0

Information concerning directors’ remuneration, pension entitlements and long-term incentive plans is shown in note 27.

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Employees

12 Months Ended

Mar. 31, 2018

Employees [Abstract]

Employees

6. Employees

		2018		2017		2016
Number of employees in the groupa	Year end 000	Average 000	Year end 000	Average 000	Year end 000	Average 000
UK	82.2	82.5	82.8	82.2	81.4	71.8
Non-UK	23.6	23.7	23.6	22.8	21.1	19.2
Total employees	105.8	106.2	106.4	105.0	102.5	91.0

		2018		2017		2016
Number of employees in the groupa	Year end 000	Average 000	Year end 000	Average 000	Year end 000	Average 000
BT Consumer	8.8	8.8	8.7	7.7	6.7	6.3
EE	9.4	9.2	9.2	9.1	9.0	1.3
Business and Public Sector	10.1	10.3	10.3	10.2	10.3	9.3
Global Services	16.9	17.3	17.5	17.4	16.8	16.5
Wholesale and Ventures	3.8	3.9	3.8	3.7	3.7	3.8
Openreach	30.5	30.4	30.2	30.9	31.5	32.1
Other	26.3	26.3	26.7	26.0	24.5	21.7
Total employees	105.8	106.2	106.4	105.0	102.5	91.0

^a These reflect the full-time equivalent of full and part-time employees.

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Audit, audit related and other non-audit services

12 Months Ended

Mar. 31, 2018

Non Audit Fees [Abstract]

Audit, audit related and other non-audit services

7. Audit, audit related and other non-auditservices

The following fees were paid or are payable to the company’s auditors, PricewaterhouseCoopers LLP and other firms in the PricewaterhouseCoopers network.

Year ended 31 March	2018 £000		2017 £000		2016 £000
Fees payable to the company’s auditors and its associates for:
Audit servicesa
The audit of the parent company and the consolidated financial statements		5,372		4,271		3,871
The audit of the company’s subsidiaries		5,866		5,664		5,073
		11,238		9,935		8,944
Audit related assurance servicesb		1,631		1,865		2,210
Other non-audit services
Taxation compliance servicesc		–		366		412
Taxation advisory servicesd		–		111		156
All other assurance servicese		211		200		1,611
All other servicesf		592		2,332		1,665
		803		3,009		3,844
Total services		13,672		14,809		14,998

^a Services in relation to the audit of the parent company and the consolidated financial statements, including fees for reports under section 404 of the Sarbanes-Oxley Act. This also includes fees payable for the statutory audits of the financial statements of subsidiary companies.

^b Services in relation to other statutory filings or engagements that are required by law or regulation to be carried out by an appointed auditor. This includes fees for the review of interim results, the audit of the group’s regulatory financial statements and reporting associated with the group’s US debt shelf registration.

^c Services relating to tax returns, tax audits, monitoring and enquiries.

^d Fees payable for all taxation advisory services not falling within taxation compliance.

^e All other assurance services include fees payable to PricewaterhouseCoopers LLP as Reporting Accountants in 2015/16 in relation to the Listing Prospectus, which was issued on 26 January 2016 for the issue of new shares.

^f Fees payable for all non-audit services not covered above, principally comprising other advisory services.

TheBTPension Scheme is an associated pension fund as definedin the Companies (Disclosure of Auditor Remuneration and Liability LimitationAgreements)(Amendment) Regulations 2011. Intheyear ended 31 March 2018 PricewaterhouseCoopers LLPreceived total fees from the BTPension Schemeof £2.1m (2016/17: £2.1m, 2015/16:£1.7m) in respect ofthefollowingservices:

Year ended 31 March	2018 £000		2017 £000		2016 £000
Audit of financial statements of associates		345		251		213
Audit-related assurance services		–		–		10
Taxation compliance services		153		210		198
Taxation advisory services		1,074		493		681
Other non-audit services		565		1,168		603
Total services		2,137		2,122		1,705

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Specific items

12 Months Ended

Mar. 31, 2018

Specific Items [Abstract]

Specific items

8. Specific items

Year ended 31 March	2018 £m			2017 £m			2016 £m
Revenue
Italian business investigation		–			22			–
Regulatory matters		23			(2	)		(203	)
EE fair value adjustment		–			–			70
		23			20			(133	)
Operating costs
EE acquisition warranty claims		225			–			–
Restructuring charges		241			–			–
EE acquisition and integration costs		46			215			113
Property rationalisation costs		28			–			29
Regulatory matters		26			481			203
Italian business investigation		22			238			–
Out of period irrecoverable VAT		–			30			–
Profit on disposal of businesses		(1	)		(16	)		–
		587			948			345
Operating loss		610			968			212
Net finance expense
Interest expense on retirement benefit obligation		218			209			221
EE related finance cost		–			–			8
Interest on out of period irrecoverable VAT		–			1			–
		218			210			229
Net specific items charge before tax		828			1,178			441
Taxation
Tax credit on specific items above		(87	)		(154	)		(70	)
Tax credit on re-measurement of deferred tax		–			(63	)		(96	)
		(87	)		(217	)		(166	)
Net specific items charge after tax		741			961			275

EE acquisition warranty claims

In the year we reached settlements with Deutsche Telekom and Orange in respect of any warranty claims under the 2015 EE acquisition agreement, arising from the issues previously announced regarding our operations in Italy. This represents a full and final settlement of these issues and resulted in a specific item charge of £225m (2016/17: £nil, 2015/16: £nil).

Restructuring charges

During the year we’ve incurred restructuring charges of £241m (2016/17: £nil, 2015/16: £nil), primarily relating to leaver costs. These costs reflect projects within the first phase of our group-wide cost transformation programme (which was announced in May 2017 and is expected to total £300m). Further associated charges relating to the first phase will be recognised in 2018/19 as part of our wider restructuring activity. See note 30 for further details.

EE acquisition and integration costs

We incurred £46m (2016/17: £215m, 2015/16: £113m) of acquisition and integration related costs for EE. Integration costs include EE related restructuring and leaver costs in the year. In 2016/17, this included a £62m (2015/16: £nil) amortisation charge relating to the write-off of IT assets as we integrated the EE and BT IT infrastructure.

Property rationalisation costs

We have recognised a charge of £28m (2016/17: £nil, 2015/16: £29m) relating to the rationalisation of the group’s property portfolio.

Regulatory matters

We’ve recognised a net charge of £49m (2016/17: £479m, 2015/16: £nil) in relation to regulatory matters in the year.  Of this, £23m is recognised in revenue and £26m in operating costs, these are made up of the following:

Deemed Consent

In 2016/17 a charge of £342m was recognised (2015/16: £nil) in relation to Ofcom’s March 2017 findings of its investigation into our historical practices on Deemed Consent by Openreach. This included a fine of £42m. We have agreed the majority of compensation payments to other Communications Providers in the year and continue to estimate the total compensation payments will amount to £300m.

Ladder pricing agreements

In 2016/17 we recognised revenue and costs of £8m (2015/16: £203m) being the prior year impacts of ladder pricing agreements with the other UK mobile operators following a Supreme Court judgment in July 2014.

Other regulatory matters

We re-assessed our regulatory risk provision in light of recent regulatory decisions by Ofcom. As a result we have increased our net charge by £49m (2016/17: £137m) for the year. £51m is recognised in provisions offset by a release of £2m in trade and other payables.

Italian business investigation

In 2017/18, we have incurred professional costs relating to the investigation of our Italian business of £22m (2016/17: £15m).

As part of the investigation into our Italian business in 2016/17, we reviewed the carrying value of the assets and liabilities on the balance sheet of our Italian business including reassessing the recoverability of trade and other receivables and reconsidering other exposures, principally tax penalties. We took into account any changes in facts or circumstances since 31 March 2016 in determining whether there was a need to change an estimate and whether additional exposures had arisen. In the prior year we recognised a charge of £245m in relation to this as well as fees in relation to the investigation of £15m.

During 2017/18 we have reassessed the prior year judgements and estimates we made as a result of the investigation into our Italian business. We concluded that the total adjustments recorded in 2016/17, either as part of the prior year revision or as a specific item, remain appropriate and thus no further adjustment is required. We identified offsetting movements in individual balance sheet line items which were not material either individually or in aggregate. These movements have been adjusted in the 2017/18 balance sheet.

Profit on disposal of businesses

During the year we disposed of non-core businesses with a gain on disposal of £1m (2016/17: £16m, 2015/16: £nil).

EE fair value adjustment

In 2015/16 we recognised a fair value adjustment on the acquisition of EE which reduced the amount of deferred income in relation to its prepaid subscriber base by £70m with no cash impact. The step down reflects the difference between the amount recorded by EE on acquisition and the fair value calculated based on the incremental cost that a market participant would incur to take on the liability plus a reasonable profit margin. This amount was released as a reduction to revenue in the period between acquisition and 31 March 2016, reflecting the period over which EE provided the related service.

Out of period irrecoverable VAT

In 2016/17, we recordeda charge of £30m for out of period irrecoverable VAT. We also recorded a further £1m related interest charge.

Interest expense on retirement benefit obligation

See note 19 for more details.

Tax credit on re-measurement of deferred tax

See note 9 for more details.

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Taxation

12 Months Ended

Mar. 31, 2018

Taxation [Abstract]

Taxation

9. Taxation

Current and deferred income tax

What critical judgements and estimates do we make in accounting for taxation?

We seek to pay taxin accordance withthelawsof the countries where we do business.However, insome areasthese laws are unclear,and it can take many yearstoagreean outcome withataxauthorityorthrough litigation.Weestimate ourtaxon country-by-countryand issue-by-issue bases.Ourkey uncertainties arewhether EE’s taxlosses will be available tous,whether ourintra-group tradingmodel will be accepted by a particulartaxauthority and whetherintra-grouppaymentsare subject to withholding taxes. Weprovide for the most likely outcome where an outflowis probable,but theagreed amountcan differmateriallyfromour estimates.Approximately 80% by value of the provisionsare underactive taxauthority examination and are thereforelikely to be re-estimatedor resolved in thecoming 12 months. £240m (2016/17:£281m) is included in current taxliabilitiesin relation tothese uncertainties.

Under a downside case an additional amount of £471mcould be required, ofwhich £382m would relatetoEElosses.Thisamountis not provided as we don’t consider thisoutcometo be probable.

Deciding whether to recognise deferred tax assets is judgemental. We only recognise them when we consider it is probable that they can be recovered. In making this judgement we consider evidence such as historical financial performance, future financial plans and trends, the duration of existing customer contracts and whether our intra-group pricing model has been agreed by the relevant tax authority.

The value of the group’s income tax assets and liabilities is disclosed on the Group balance sheet on page 108. The value of the group’s deferred tax assets and liabilities, including the deferred tax asset recognised in respect of EE Limited’s historical tax losses, is disclosed below.

Analysisofourtaxationexpensefortheyear

Year ended 31 March	2018 £m			2017 £m			2016 £m
United Kingdom
Corporation tax at 19% (2016/17: 20%, 2015/16: 20%)		(614	)		(594	)		(684	)
Adjustments in respect of earlier years		37			33			59
Non-UK taxation
Current		(66	)		(109	)		(80	)
Adjustments in respect of earlier years		23			–			29
Total current tax expense		(620	)		(670	)		(676	)
Deferred taxation
Origination and reversal of temporary differences		46			96			70
Adjustments in respect of earlier years		(57	)		26			2
Impact of change in UK corporation tax rate to 17% (2016/17: 17%, 2015/16: 19%)		–			63			96
Remeasurement of temporary differences		11			–			–
Total deferred taxation credit		–			185			168
Total taxation expense		(620	)		(485	)		(508	)

Factorsaffectingourtaxationexpensefor theyear

Thetaxationexpense on the profitforthe year differs fromtheamount computed byapplying theUK corporation taxrate totheprofit beforetaxation as a result ofthefollowingfactors:

Year ended 31 March	2018 £m			2017 £m			2016 £m
Profit before taxation		2,804			2,551			3,241
Expected taxation expense at UK rate of 19% (2016/17: 20%, 2015/16: 20%)		(533	)		(510	)		(648	)
Effects of:
(Higher) lower taxes on non-UK profits		(8	)		(29	)		4
Net permanent differences between tax and accountinga		(100	)		(183	)		(12	)
Adjustments in respect of earlier yearsb		3			59			90
Prior year non-UK losses used against current year profits		16			120			9
Non-UK losses not recognisedc		(9	)		(8	)		(34	)
Other deferred tax assets not recognised		–			–			6
Lower taxes on profit on disposal of business		–			3			–
Re-measurement of deferred tax balances		11			63			96
Other non-recurring items		–			–			(19	)
Total taxation expense		(620	)		(485	)		(508	)
Exclude specific items (note 8)		(87	)		(217	)		(166	)
Total taxation expense before specific items		(707	)		(702	)		(674	)

^a Includes income that is not taxable or UK income taxable at a different rate, and expenses for which no tax relief is received. Examples include some types of depreciation and amortisation and the benefit of R&D tax incentives.

^b Reflects the differences between initial accounting estimates and tax returns submitted to tax authorities, including the release and establishment of provisions for uncertain tax positions.

^c Reflects lossesmadeincountrieswhereit hasnotbeenconsideredappropriateto recogniseadeferredtaxasset,asfuturetaxableprofitsarenotprobable.

Taxcomponentsofothercomprehensiveincome

Year ended 31 March	2018 Tax credit (expense) £m			2017 Tax credit (expense) £m			2016 Tax credit (expense) £m
Tax on items that will not be reclassified to the income statement
Pension remeasurements		(346	)		416			(240	)
Tax on items that have been or may be reclassified subsequently to the income statement
Exchange differences on translation of foreign operations		(9	)		21			38
Fair value movements on cash flow hedges
– net fair value gains or losses		57			(131	)		(72	)
– recognised in income and expense		(47	)		139			39
		(345	)		445			(235	)
Current tax credita		203			122			231
Deferred tax (expense) credit		(548	)		323			(466	)
		(345	)		445			(235	)

^a Includes£212m(2016/17:£110m,2015/16:£217m)relatingtocashcontributionsmadetoreduceretirementbenefitobligations.

Tax(expense)creditrecogniseddirectlyinequity

Year ended 31 March	2018 £m			2017 £m			2016 £m
Tax (expense) credit relating to share-based payments		(2	)		(6	)		12

Deferred taxation

	Fixed asset temporary differences £m			Retirement benefit obligations £m		a	Share- based payments £m			Tax losses £m			Other £m			Jurisdictional offset £m			Total £m
At 1 April 2016		1,618			(1,149	)		(54	)		(325	)		(75	)		–			15
(Credit) expense recognised in the income statement		(181	)		(82	)		14			65			(1	)		–			(185	)
(Credit) expense recognised in other comprehensive income		(5	)		(306	)		–			(3	)		(9	)		–			(323	)
Expense recognised in equity		–			–			23			–			–			–			23
Exchange differences		–			–			–			(7	)		–			–			(7	)
At 31 March 2017		1,432			(1,537	)		(17	)		(270	)		(85	)		–			(477	)
Non-current
Deferred tax asset		(117	)		(1,537	)		(17	)		(270	)		(96	)		320			(1,717	)
Deferred tax liability		1,549			–			–			–			11			(320	)		1,240
At 1 April 2017		1,432			(1,537	)		(17	)		(270	)		(85	)		–			(477	)
Expense (credit) recognised in the income statement		11			(104	)		4			89			–			–			–
Expense (credit) recognised in other comprehensive income		–			558			–			–			(10	)		–			548
Expense recognised in equity		–			–			6			–			–			–			6
Exchange differences		–			–			–			(2	)		5			–			3
Transfer to current tax		17			–			–			–			–			–			17
At 31 March 2018		1,460			(1,083	)		(7	)		(183	)		(90	)		–			97
Non-current
Deferred tax asset		(41	)		(1,083	)		(7	)		(183	)		(90	)		161			(1,243	)
Deferred tax liability		1,501			–			–			–			–			(161	)		1,340
At 31 March 2018		1,460			(1,083	)		(7	)		(183	)		(90	)		–			97

^a Includesa deferredtaxassetof£2m(2016/17:£2m)arisingon contributionspayableto definedcontributionpensionplans.

Themajorityof the deferred taxassetsand liabilitiesnoted aboveare anticipated toberealisedaftermore than12 months.

We’verecognised a deferred taxasset at31 March 2018 of£92m in respect ofEELimited’shistoricaltaxlosses. We expectto be able toutilise theseagainstfuturetaxableprofitsin EELimited. IfEELimited’s businesshad been subject toa major change in the nature or conductoftrade on orbefore 5 February2018,theselosses would have been forfeitedand a current taxliabilityof£382m would have been created. We do not consider it probable that major change arose.

Deferred tax balancesfor whichthere is a right of offsetwithin thesame jurisdiction arepresentednet on theface of thegroup balance sheet as permittedby IAS12, with theexceptionof deferredtaxrelated to ourpension schemes which is disclosed within deferredtax assets.

Whatfactorsaffect ourfuturetax charges?

Therate ofUK corporation taxwill change from19% to17% on1 April 2020.Asdeferredtaxassets and liabilities are measured at the ratesthat are expected toapply intheperiodsof the reversal,deferredtaxbalancesat 31 March 2018 have been calculated attherate atwhich the relevantbalanceis expected tobe recovered or settled.The impact of thereduction inrate wasrecognised as a deferred tax credit specific item of £63m in the 2016/17 income statement and as a deferred taxexpense in reserves.

Whatare ourunrecognisedtax lossesandothertemporary differences?

At31 March 2018 we had operating losses and other temporary differencescarried forwardin respectof which no deferredtaxassets were recognised amounting to£4.1bn(2016/17:£4.4bn).Ourother temporary differenceshave no expiry date restrictions. Theexpiry dateof operating losses carried forward is dependentupon the taxlaw ofthe various territoriesin which thelosses arose.A summary of expiry dates for losses in respect ofwhich restrictionsapply is set out below:

At 31 March 2018	£m		Expiry
Restricted losses
Europe		14	2019–2027
Americas		204	2019-2037
Other		2	2019–2027
Total restricted losses		220
Unrestricted operating losses		3,784	No expiry
Other temporary differences		77	No expiry
Total		4,081

At31 March 2018 we had UK capitallosses carried forward in respect ofwhich no deferred taxassetswere recognised amountingto £16.9bn (2016/17: £17.0bn).Theselosses have no expiry date,but we consider thefutureutilisation ofthese lossestobe remote.

At31 March 2018 the undistributedearnings ofnon-UK subsidiaries were £2.4bn (2016/17:£3.5bn). No deferred taxliabilities have been recognised in respect oftheseunremittedearnings because thegroup is in a position tocontrol the timing ofanydividends from subsidiariesand hence any taxconsequences thatmay arise. Undercurrent taxrules,taxof£23.0m (2016/17:£26.2m)would arise if theseearnings were tobe repatriated totheUK.On29 March 2017,theUK Governmentnotified the EU of its intentiontowithdraw membership from the EU. Depending on the outcome ofnegotiations we could cease tobenefit from theEU ParentSubsidiarydirective on dividendspaid by ourEU subsidiaries. Inthisevent,additional taxofup to £23.9mcould arise ifthe undistributed earnings of EU subsidiariesof £940mwere tobe repatriated tothe UK.

XML

Dividends

12 Months Ended

Mar. 31, 2018

Dividend [Abstract]

Dividends

10. Dividends

Whatdividendshavebeenpaidandproposedforthe year?

No dividend was paid to the parent company, BT Group Investments Limited, during 2017/18 (2016/17: £2,350m, 2015/16: £1,450m).

Subsequent to 31 March 2018 the directors have declared a final dividend of £2,500m payable in 2018/19 (2016/17: £nil, 2015/16: £2,350m).

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Intangible assets

12 Months Ended

Mar. 31, 2018

Intangible Assets [Abstract]

Intangible assets

11. Intangible assets

	Goodwill £m			Customer relationships and brands £m			Telecoms licences and other £m			Internally developed software £m			Purchased software £m			Total £m
Cost
At 1 April 2016		7,915			3,401			2,930			4,073			1,610			19,929
Acquisitions		5			–			–			–			–			5
Additions		–			–			–			483			138			621
Disposals and adjustmentsa		(23	)		–			–			(131	)		2			(152	)
Transfers		–			–			–			(66	)		62			(4	)
Exchange differences		145			21			15			4			41			226
At 31 March 2017		8,042			3,422			2,945			4,363			1,853			20,625
Additions		–			–			–			517			125			642
Acquisitions		14			–			3			–			–			17
Disposals and adjustmentsa		(3	)		–			(3	)		(55	)		(413	)		(474	)
Exchange differences		(100	)		(12	)		6			(3	)		9			(100	)
At 31 March 2018		7,953			3,410			2,951			4,822			1,574			20,710
Accumulated amortisation
At 1 April 2016		–			418			131			2,747			1,175			4,471
Charge for the yearb		–			383			140			556			101			1,180
Disposals and adjustmentsa		–			–			–			(114	)		(7	)		(121	)
Exchange differences		–			12			9			4			33			58
At 31 March 2017		–			813			280			3,193			1,302			5,588
Charge for the yearb		–			379			141			525			78			1,123
Disposals and adjustmentsa		–			–			(3	)		(36	)		(426	)		(465	)
Exchange differences		–			(1	)		3			(2	)		9			9
At 31 March 2018		–			1,191			421			3,680			963			6,255
Carrying amount
At 31 March 2018		7,953			2,219			2,530			1,142			611			14,455
At 31 March 2017		8,042			2,609			2,665			1,170			551			15,037

^aFully depreciated assets in the group’s fixed asset registers were reviewed during the year, as part of the group’s annual asset verification exercise, and certain assets that were no longer in use have been written off, reducing cost and accumulated depreciation by £0.4bn (2016/17: £nil).

^b   Includesa £nil(2016/17: £62m)specificitemamortisationchargerelatingtothewrite-offofinternallydevelopedsoftwareasweintegratetheEEandBTITinfrastructure.

Goodwill

Goodwill recognised in a businesscombination doesnot generate cash flowsindependently ofother assets or groups of assets.Asa result,therecoverable amount,being thevalue inuse, is determinedata cash generating unit(CGU)level.

HowdowedetermineourCGUs?

Thedetermination of ourCGUsisjudgemental. TheidentificationofCGUsinvolves anassessment ofwhether theasset or group of assetsgenerate largely independentcash inflows.Thisinvolvesconsideration of how our core assetsare operatedand whether these generateindependent revenuestreams.OurCGUs aredeemed tobe BT Consumer, EE,Business andPublic Sector,Global Services and Wholesaleand Ventureswhich are the same unitswe reportin our segmentalreporting.

Forimpairment purposes goodwill is testedatthelowestlevelwithin theentityatwhich the goodwill is monitored forinternal managementpurposes, and cannot be larger thanour operating segments.We testgoodwill at the CGUlevel.

Whatcriticalestimates andassumptionshavewemade?

In 2016/17 we re-allocated goodwill among our CGUs based onthe relative fairvalue ofthebusinesstransferredtoreflectour new customer-facing units structureeffectiveas of 1 April 2016. We estimated the relative fairvalues on a discounted cash flow basisusing the three-year financial plans effectiveatthetime ofthere-organisation.Theassumptionsused were set in thesame way as those used in our value in use calculations as setout below.

Ourvalue in use calculations require estimates in relation to uncertainitems,including management’s expectations offuturerevenue growth,operating costs,profit margins, operating cashflows,andthe discount rate foreach CGU.

Future cash flows used in the value in use calculations are based on our latest BT Group plc Board approved five-year financial plans. Expectations about future growth reflect the expectations of growth in the markets to which the CGU relates. The future cash flows are discounted using a pre-tax discount rate that reflects current market assessments of the time value of money. The discount rate used in each CGU is adjusted for the risk specific to the asset, including the countries in which cash flow will be generated, for which the future cash flow estimates have not been adjusted.

Thegroup is required totestgoodwill acquired in a business combination annually forimpairment.Thiswascarried out as at31January 2018. Thecarrying value of goodwill and thekey assumptions used in performingtheannual impairmentassessmentand sensitivities are disclosed below.

How havewecarriedoutourgoodwillimpairmentreview?

Weperform an annual goodwill impairmentreview,based on our CGUs.

TheseCGUs representthesmallestidentifiable groups ofassetsthatgenerate cash inflows thatare largely independentof thecash inflows fromother groupsof assets,and to which goodwill isallocated. From1 April 2016, we re-organised our customer-facing unitsresulting in thechange of the CGUsthat have associated goodwill.Weallocatedgoodwill to BT Consumer,EE,Business and PublicSector,Global Servicesand Wholesale and Ventures. Previouslyno goodwill was allocatedtoWholesale and Ventures.Inaddition to goodwill being allocated to this CGU for the first time, therewere changes totheamount allocated to the other CGUs asa result ofthere-organisation. Goodwill is allocated tothese CGUs as follows:

Cost	BT Consumer £m		EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m		Total £m
At 1 April 2016		1,183		4,917			662			1,153			–		7,915
Re-organisation		–		(2,149	)		1,921			(709	)		937		–
Exchange differences		–		–			10			135			–		145
Acquisitions and disposals		–		–			(23	)		–			5		(18	)
At 31 March 2017		1,183		2,768			2,570			579			942		8,042
Exchange differences		–		–			(8	)		(92	)		–		(100	)
Acquisitions and disposals		–		–			–			11			–		11
At 31 March 2018		1,183		2,768			2,562			498			942		7,953

Howdowecalculatetherecoverableamount?

Thevalue in use ofeachCGU is determined using cash flow projections derivedfromfinancial plans approved by the BT Group plcBoard coveringa five-yearperiod. Theyreflectmanagement’s expectations ofrevenue,EBITDAgrowth,capitalexpenditure, working capitaland operating cash flows,based on pastexperience and futureexpectationsofbusinessperformance. Cash flows beyond thefifth year have been extrapolated using perpetuity growthrates.

Whatdiscountrate havewe used?

Thepre-tax discount ratesapplied tothe cashflow forecastsare derived from our post-tax weighted average costof capital. The assumptionsused inthecalculation of the group’s weighted average costof capital are benchmarkedtoexternallyavailable data.The pre-tax discountrate used in performingthevalue in use calculation in 2017/18 was 8.4% (2016/17:8.6%).We’veused thesame discount rate forall CGUsexcept Global Serviceswhere we have used 8.8% (2016/17: 9.0%) reflecting higherriskin some of the countriesin which Global Servicesoperates.

Whatgrowthrates haveweused?

Theperpetuity growthrates aredetermined based ontheforecastmarketgrowthrates oftheregionsin which the CGU operates,and they reflect an assessmentof the long-term growthprospectsof that market.Thegrowthrates have been benchmarked againstexternal data for the relevantmarkets.Noneofthegrowth ratesapplied exceed the expectedlong-term average growthrates forthosemarketsor sectors.Theperpetuitygrowthrate forGlobal Services was2.3% (2016/17:2.4%) and 2.0% (2016/17:2.0%)forBusinessand Public Sector, BT Consumer, EEand Wholesaleand Ventures.

Whatsensitivitieshave we applied?

Thereis significant headroom in Business and PublicSector, BT Consumer, Wholesale and Ventures and EE.No reasonably possible changesin thekey assumptions in isolation would cause the carrying amountoftheCGUs toexceed therecoverable amount.ForGlobal Services, thevalue in use exceedsthe carrying value oftheCGU by approximately £768m(2016/17:£586m).Any ofthefollowingchangesin assumptions in isolationwould cause therecoverable amountforthe CGUtoequal itscarrying amount:

–reductionin the perpetuitygrowthratefromthe 2.3%assumptionapplied toa revised assumption ofa decline of 1.4%.

–an increase in the discount rate fromthe 8.8% assumption applied toa revisedassumption of 11.5%.

–shortfallsin trading performance againstforecastresulting in operating cash flows decreasing by 34% each year andin perpetuity.

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Property, plant and equipment

12 Months Ended

Mar. 31, 2018

Disclosure Of Property Plant And Equipment [Abstract]

Property, plant and equipment

12. Property, plant and equipment

Theplant andequipmentin our networksislong-lived withcables and switching equipment operating forover ten years andunderground ducts beingusedfordecades.Wealso develop software foruse inITsystemsandplatforms thatsupportthe products and services providedtoour customers.

Thecarrying values ofsoftware, property,plant andequipment are disclosed below and in note11. Theuseful lives applied to the principal categories ofassetsare disclosed on pages 115 and 116.

	Land and   buildings £m		a	Network   infrastructure £m		a	Other £m		b	Assets in course of construction £m			Total £m
Cost
At 31 March 2016		1,278			48,194			1,870			1,108			52,450
Additionsc		6			40			128			2,672			2,846
Transfers		14			2,393			(1	)		(2,402	)		4
Disposals and adjustmentsd		(45	)		(1,637	)		(106	)		30			(1,758	)
Exchange differences		49			382			47			5			483
At 31 March 2017		1,302			49,372			1,938			1,413			54,025
Additionsc		12			193			92			2,597			2,894
Transfers		36			2,793			16			(2,845	)		–
Disposals and adjustmentsd		(82	)		(1,540	)		(119	)		(48	)		(1,789	)
Exchange differences		(6	)		(35	)		(13	)		1			(53	)
At 31 March 2018		1,262			50,783			1,914			1,118			55,077
Accumulated depreciation
At 31 March 2016		750			34,287			1,513			–			36,550
Charge for the year		64			2,224			104			–			2,392
Disposals and adjustmentsd		(36	)		(1,627	)		(104	)		–			(1,767	)
Exchange differences		39			330			41			–			410
At 31 March 2017		817			35,214			1,554			–			37,585
Charge for the year		57			2,213			121			–			2,391
Disposals and adjustmentsd		(96	)		(1,613	)		(107	)		–			(1,816	)
Exchange differences		(5	)		(24	)		(10	)		–			(39	)
At 31 March 2018		773			35,790			1,558			–			38,121
Carrying amount
At 31 March 2018		489			14,993			356			1,118			16,956
Engineering stores		–			–			–			44			44
Total at 31 March 2018		489			14,993			356			1,162			17,000
At 31 March 2017		485			14,158			384			1,413			16,440
Engineering stores		–			–			–			58			58
Total at 31 March 2017		485			14,158			384			1,471			16,498

^a The carrying amount of the group’s property, plant and equipment includes an amount of £53m (2016/17: £73m) in respect of assets held under finance leases, comprising land and buildings of £42m (2016/17: £45m) and network infrastructure of £11m (2016/17: £28m). The depreciation expense on those assets in 2017/18 was £10m (2016/17: £10m), comprising land and buildings of £3m (2016/17: £3m) and network infrastructure of £7m (2016/17: £7m).

^b Other mainly comprises motor vehicles, computers and fixtures and fittings.

^c Net of grant funding of £74m (2016/17: £28m net grant deferral).

^d Fully depreciated assets in the group’s fixed asset registers were reviewed during the year, as part of the group’s annual asset verification exercise, and certain assets that were no longer in use have been written off, reducing cost and accumulated depreciation by £1.3bn (2016/17: £1.1bn).

At 31 March	2018 £m		2017 £m
The carrying amount of land and buildings, including leasehold improvements, comprised:
Freehold		261	269
Leasehold		228	216
Total land and buildings		489	485

Networkinfrastructure

Someofournetwork assetsare jointly controlled by EELimited with Hutchison 3GUK Limited. These relatetoshared 3Gnetwork and certain elements of network for 4Grural sites.The net book value ofthegroup’s share of assets controlled by its joint operation MBNL is £526m(2016/17: £591m) and is recorded within networkinfrastructure. Included withinthis is £132m(2016/17: £179m),being thegroup’sshare of assets owned byits joint operation MBNL.

Withinnetwork infrastructureare assetswitha net book value of £8.3bn (2016/17: £8.0bn) which have useful economiclives ofmore than 18 years.

Whatestimates andcriticaljudgementshavewe madeinaccountingforourBDUK contracts?

Thegroup receives government grantsin relationtotheBDUKprogrammeandother rural superfastbroadbandcontracts.Wherewe’ve achievedcertain service levels, ordeliveredthenetwork moreefficiently than anticipated,we’ve an obligation toeitherre-investor repay grant funding. Wherethis is thecase,weassessand deferthe income witha corresponding increase in capital expenditure.

Assessing the timing of whether and when wechange theestimatedtake-up assumptionis judgementalas it involves considering information which isnot always observable. Ourconsiderationon whetherand whentochange the base case assumptionis dependent

on our expectationofthelongterm take-uptrend.

Ourassessmentof how much grant income todeferincludesconsideration of the differencebetweenthetake-uppercentage agreed with thelocal authorityand thelikelihood ofactual take-up.The value ofthegovernmentgrantsdeferredis disclosedin note17.

In the current year we had a net grant funding of £74m (2016/17: £28m net grant deferral) mainly related to our activity on the BDUK programme. Our base case assumption for take-up in BDUK areas has been increased to 41% (2016/17: 39%) following our review of the level of customer take-up. Based on the current build, a change in the take-up assumption of 4% would result in approximately a £50m movement in the amount deferred. To date we have a grant funding liability of £536m (2016/17: £446m).

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Business combinations

12 Months Ended

Mar. 31, 2018

Disclosure Of Business Combinations [Abstract]

Business combinations

13. Business combinations

All business combinations are accounted for using the acquisition method regardless of whether equity instruments or other assets are acquired. We didn’t make any material acquisitions in the year ended 31 March 2018 (2016/17: no material acquisitions). The acquisition of EE was completed in 2015/16 with the provisional acquisition accounting at 31 March 2016 and the final acquisition accounting was reflected during 2016/17.

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Programme rights

12 Months Ended

Mar. 31, 2018

Disclosure Of Programme Rights [Abstract]

Programme rights

14. Programmerights

	Total £m
At 1 April 2016		225
Additions		753
Amortisation		(714	)
At 1 April 2017		264
Additions		771
Amortisation		(763	)
At 31 March 2018		272

AdditionsreflectTVprogramme rights forwhich thelegally enforceablelicence period has started during the year.Paymentsmade for programme rightsforwhich thelegally enforceable licence period has not yet started are included withinprepayments(see note 16).

TVprogramme rightscommitmentsare disclosed in note 29.

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Inventories

12 Months Ended

Mar. 31, 2018

Inventories [Abstract]

Inventories

15. Inventories

At 31 March	2018 £m		2017 £m	2016 £m
Consumables		22	24	26
Work in progress		6	23	11
Finished goods		211	180	152
		239	227	189

Inventoriesrecognised asan expense during theyear ended 31 March 2018 amounted to£2,588m(2016/17:£2,680m).These were included in ‘Operatingcosts’ in our income statement.

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Trade and other receivables

12 Months Ended

Mar. 31, 2018

Disclosure Of Trade And Other Receivables [Abstract]

Trade and other receivables

16. Trade and other receivables

We’ve made various judgements in accounting for trade and other receivables. These include long-term contracts and bad debt provisions.

Long-term customer contracts

Long-term customer contracts can extend over a number of financial years. During the contractual period recognition of costs and profits may be impacted by judgements and estimates made.

What critical estimates and assumptions have we made?

Estimates are required in assessing the lifetime profitability of a contract when determining whether we have an onerous contract liability. Where we have an onerous contract liability this would be classified in provisions and include an impairment of any receivables relating to these contracts.

The level of uncertainty in the estimates and assumptions supporting expected future revenues and costs can vary with the complexity of each contract and with the form of service delivery.

We've exercised judgement in assessing when the transition or transformation phase of a contract ends. This influences the timing of recognition of revenue and costs which are deferred until the transition or transformation phase ends unless these elements of a contract have standalone value.

How do we estimate and recognise contract losses?

We estimate and recognise immediately the entire estimated loss for a contract when we have evidence that the contract is unprofitable. Also if these estimates indicate that any contract will be less profitable than previously forecast, contract assets may have to be written down to the extent they are no longer considered to be fully recoverable. We perform ongoing profitability reviews of our contracts in order to determine whether the latest estimates are appropriate. Key factors reviewed include:

– Transaction volumes or other inputs affecting future revenues which can vary depending on customer requirements, plans, market position and other factors such as general economic conditions.

– Our ability to achieve key contract milestones connected with the transition, development, transformation and deployment phases for customer contracts.

– The status of commercial relations with customers and the implication for future revenue and cost projections.

– Our estimates of future staff and third-party costs and the degree to which cost savings and efficiencies are deliverable.

The carrying value of assets comprising the costs of the initial set-up, transition or transformation phase of long-term networked IT services contracts is disclosed below.

At 31 March	2018 £m	2017 £m	2016 £m
Non-current
Other assetsa	317	360	218

^a Other assets includes costs relating to the initial set-up, transition or transformation phase of long-term networked IT services contracts of £145m (2016/17: £163m, 2015/16: £111m), and prepayments and leasing debtors of £172m (2016/17: £197m, 2015/16: £107m).

At 31 March	2018 £m		2017 £m		2016 £m
Current
Trade receivables		1,741		1,774		1,803
Amounts owed by ultimate parent company		15		25		9
Prepaymentsa		1,103	733		702
Accrued income		777	955			1,072
Other receivablesb	393		373		401
		4,029		3,860		3,987

^aPrepayments includes £325m (2016/17: £nil, 2015/16: £nil) in respect of the acquisition of spectrum in April 2018. The spectrum auction bidding cut across the 2017/18 and 2018/19 financial years. Whilst £325m was on deposit with Ofcom at 31 March 2018, we went on to win spectrum for a total price of £304m and the excess deposit balance has since been refunded. This will be transferred to intangible assets in 2018/19.

^bOther receivables includes assets held for sale of £nil (2016/17: £22m, 2015/16: £nil).

Trade receivables are stated after deducting allowances for doubtful debts, as follows:

	2018 £m			2017 £m			2016 £m
At 1 April	303			195			196
Expense	129			211			77
Utilised		(61	)		(114	)		(89	)
Exchange differences	4			11			11
At 31 March	375			303			195

Included within the 2016/17 expense above are amounts for exposures relating to the Italian business investigation, as set out in note 8.

How do we assess recoverability of our receivables?

We provide services to consumer and business customers, mainly on credit terms. We know that certain debts due to us will not be paid through the default of a small number of our customers. Judgements are required in assessing the recoverability of trade receivables and whether a provision for doubtful debts may be required.

In estimating a provision for doubtful debts we consider historical experience alongside other factors such as the current state of the economy and particular industry issues. The value of the provision for doubtful debts is disclosed above.

Trade receivables are continuously monitored and allowances applied against trade receivables consist of both specific impairments and collective impairments based on our historical loss experiences for the relevant aged category as well as taking into account general economic conditions. Historical loss experience allowances are calculated by a customer-facing unit in order to reflect the specific nature of the customers relevant to that customer-facing unit.

Trade and other receivables are classified as loans and receivables and are held at amortised cost. The carrying amount of these balances approximates to fair value due to the short maturity of amounts receivable.

Note 25 provides further disclosure regarding the credit quality of our gross trade receivables. Trade receivables are due as follows:

					Past due and not specifically impaired
At 31 March	Not past due £m		Trade receivables specifically impaired net of provision £m		Between 0 and 3 months £m		Between 3 and 6 months £m		Between 6 and 12 months £m		Over 12 months £m		Total £m
2018		1,251		61		293		44		25		67		1,741
2017		1,184		146		292		17		41		94		1,774
2016		1,152		98		368		51		44		90		1,803

Gross trade receivables which have been specifically impaired amounted to £124m (2016/17: £238m, 2015/16: £192m).

Trade receivables not past due and accrued income are analysed below by customer-facing unit.

	Trade receivables not past due						Accrued income
At 31 March	2018 £m		2017 £m		2016 £m		2018 £m		2017 £m		2016 £m
BT Consumer		157		128		138		86		90		83
EE		206		335		267		122		170		312
Business and Public Sector		253		200		115		134		151		146
Global Services		477		444		555		222		297		351
Wholesale and Ventures		92		75		76		145		167		99
Openreach		61		1		1		67		78		79
Other		5		1		–		1		2		2
Total		1,251		1,184		1,152		777		955		1,072

Given the broad and varied nature of our customer base, the analysis of trade receivables not past due and accrued income by customer-facing unit is considered the most appropriate disclosure of credit concentrations. Cash collateral held against trade and other receivables amounted to £6m (2016/17: £4m, 2015/16: £4m).

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Trade and other payables

12 Months Ended

Mar. 31, 2018

Trade And Other Payables [Abstract]

Trade and other payables

17. Trade and other payables

At 31 March	2018 £m		2017 £m		2016 £m
Current
Trade payables		3,991		4,205		4,331
Amounts owed to parent company		50		63		70
Other taxation and social security		704		704		682
Other payables		428		648		527
Accrued expenses		492		382		418
Deferred incomea		1,525		1,474		1,435
		7,190		7,476		7,463

At 31 March	2018 £m		2017 £m		2016 £m
Non-current
Other payablesb		871		885		876
Deferred incomea		455		413		230
		1,326		1,298		1,106

^a Includes £132m (2016/17: £71m, 2015/16: £71m) current and £404m (2016/17: £375m, 2015/16: £187m) non-current liabilities relating to the Broadband Delivery UK programme, for which grants received by the group may be subject to re-investment or repayment depending on the level of take-up.

^b Other payables relate to operating lease liabilities and deferred gains on a 2001 sale and finance leaseback transaction.

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Provisions

12 Months Ended

Mar. 31, 2018

Provisions [Abstract]

Provisions

18. Provisions

Provisionsandcontingentliabilities

As disclosed below, our provisions principally relate to obligations arising from property rationalisation programmes, restructuring programmes, asset retirement obligations, network assets, insurance claims, litigation and regulatory risks.

Whatcriticaljudgementshavewemadeinaccountingforprovisions?

We exercise judgement in determining the timing and quantum of all provisions to be recognised. Our assessment includes consideration of whether we have a present obligation, whether payment is probable and if so whether the amount can be estimated reliably. As part of this assessment, we also assess the likelihood of contingent liabilities occurring in the future which are not recognised as liabilities on our balance sheet. By their nature, contingencies will be resolved only when one or more uncertain future events occur or fail to occur. We assess the likelihood that a potential claim or liability will arise and also quantify the possible range of financial outcomes where this can be reasonably determined.  We’ve disclosed our assessment of contingent liabilities in note 29.

Whatothercriticalestimates andassumptionshavewemade?

Restructuring programmes involve estimation of the direct cost necessary for the restructuring and exclude items that are associated with ongoing activities. The amounts below exclude restructuring costs for which the timing and amount are certain. These are recognised as part of trade and other payables.

Under our property rationalisation programmes we’ve identified a number of surplus properties. Although efforts are being made to sublet this space, this is not always possible. Estimates have been made of the cost of vacant possession and of any shortfall arising from any potential sub-lease income being lower than the lease costs. Any such shortfall is recognised as a provision.

Asset retirement obligations involve an estimate of the cost to dismantle equipment and restore sites upon vacation and the timing of the event. The provision represents the group’s best estimate of the amount that may be required to settle the obligation.

Network asset provisions represent our future operational costs and vacant site rentals arising from obligations relating to network share agreements. Costs are expected to be incurred over a period of up to 20 years.

Our regulatory provision represents our best estimate of the cost to settle our present obligation in relation to historical regulatory matters. The charge for the year represents the outcome of management’s re-assessment of the estimates and regulatory risks across a range of issues, including price and service issues.  The prices at which certain services are charged are regulated and may be subject to retrospective adjustment by regulators.  Estimates are used in assessing the likely value of the regulatory risk. 

In 2016/17 we recognised a £300m charge in relation to estimated Deemed Consent compensation payments. The precise amount of the compensation payments will result from discussions with the affected parties and as of 31 March 2018, we still consider this estimate to be appropriate.  In 2016/17 a related fine of £42m was imposed and was recognised as a payable rather than as a provision. The fine and associated compensation payments totaling £342m were treated as a specific item charge in last year’s income statement. The remaining provision increases also reflected management’s estimates of regulatory risks across a range of issues, including price and service issues. These increased by £51m (2016/17: £126m), also treated as specific items, resulting from our re-assessment of these other regulatory risks and in light of the regulatory decisions by Ofcom.

In respect of claims, litigation and regulatory risks, the group provides for anticipated costs where an outflow of resources is considered probable and a reasonable estimate can be made of the likely outcome.

Included within Other are contract loss provisions of £38m (2016/17: £29m) relating to the anticipated total losses in respect of certain contracts.  It is expected that the majority of these provisions will be utilised in the next few years.  Given the short period remaining to the finalisation of these contracts, any potential future changes to key assumptions made when estimating their future losses are not expected to have a significant impact.  There is no single change in key variables that could materially affect future expected losses on these contracts.  Also included in Other are amounts provided for the constructive obligations arising from insurance claims which will be utilised as the obligations are settled and amounts provided for exposures relating to the Italian business investigation, principally potential tax penalties.

For all risks, the ultimate liability may vary from the amounts provided and will be dependent upon the eventual outcome of any settlement. The estimates are discounted using a rate that reflects the passage of time and risk specific to the liability. An estimate is also required in assessing the timing of when a provision is recognised. The outcome of our estimate of the provisions is disclosed below.

	Restructuring £m		a	Property £m			Network ARO £m			Network share £m			Regulatory £m			Litigation £m			Other £m			Total £m
At 31 March 2016		20			296			78			60			64			73			152			743
Income statement expense	–				38			27			5			426			6			34			536
Unwind of discount	–				12			2			2		–			–			–				16
Utilised or released		(10	)		(54	)		(24	)		(17	)		(11	)		(11	)		(8	)		(135	)
Transfers	–			–			–			–			–			–				(3	)		(3	)
Exchange  differences		1			–			–			–			–		1				2			4
At 31 March 2017		11			292			83			50			479			69			177			1,161
Income statement expense	4				37			2		–				51			6			33			133
Unwind of discount	–				11			2			2		–			–			–				15
Utilised or released		(2	)		(46	)		(16	)		(19	)		(210	)		(11	)		(32	)		(336	)
Transfers	–			–			–			–			–			–				85			85
Exchange  differences		(1	)	–			–			–			–			–				(2	)		(3	)
At 31 March 2018		12			294			71			33			320			64			261			1,055

^a  Restructuring costs for which the timing and amount are certain. These amounts are reflected in trade and other payables.

At 31 March	2018 £m		2017 £m		2016 £m
Analysed as:
Current		603		625		178
Non-current		452		536		565
		1,055		1,161		743

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Retirement Benefit Plans

12 Months Ended

Mar. 31, 2018

Disclosure Of Defined Benefit Plans [Abstract]

Retirement Benefit Plans

19. Retirement benefit plans

Background to BT’s pension plans

The group has both defined benefit and defined contribution retirement benefit plans. The group’s main plans are in the UK and the largest by membership is the BT Pension Scheme (BTPS) which is a defined benefit plan that was closed to new entrants on 31 March 2001. After that date new entrants to BT in the UK have been able to join a defined contribution plan, currently the BT Retirement Saving Scheme (BTRSS), a contract-based arrangement.

In March 2018, BT announced the closure of Sections B and C of the BTPS to future benefit accrual (which represents over 99% of the BTPS active membership), having reached an agreement with the relevant Unions. BT currently expects to close the BTPS from 30 June 2018 when employees will join the BTRSS for future pension accrual.

EE operates the EE Pension Scheme (EEPS), which has a defined benefit section that was closed to future benefit accrual in 2014 and a defined contribution section which is open to new joiners.

	Whatarethey?	Howdothey impact BT’sfinancialstatements?
Definedcontributionplans	Benefitsina definedcontributionplan arelinkedto: –  contributionspaid –  theperformanceofeachindividual’s choseninvestments –  theforminwhichindividualschoose totaketheirbenefits. Contributionsarepaidintoan independentlyadministeredfund.	Theincomestatementchargeinrespectof definedcontributionplans representsthecontributionpayablebythegroupbaseduponafixed percentageofemployees’pay. Thegrouphasnoexposuretoinvestmentandotherexperiencerisks.
Definedbenefitplans	Benefitsina definedbenefitplanare: –  determinedbytheplanrules, dependentonfactorssuchasage, yearsofserviceandpensionable pay –  notdependentuponactual contributionsmadebythecompany ormembers.	Theincomestatementservicecost inrespectofdefinedbenefitplans representstheincreaseinthedefinedbenefitliabilityarisingfrompension benefitsearnedbyactivemembersinthecurrentperiod. Thegroupisexposedtoinvestmentandotherexperiencerisksandmayneed tomakeadditionalcontributionswhereit isestimatedthatthebenefitswillnot bemetfromregularcontributions,expectedinvestmentincomeandassets held.

Amounts in the financial statements

Group income statement

The expense or income arising from all group retirement benefit arrangements recognised in the group income statement is shown below.

Year ended 31 March	2018 £m			2017 £m		2016 £m
Recognised in the income statement before specific items
Service cost (including administration expenses & PPF levy):
– defined benefit plans		376			281		301
– defined contribution plans		265			240		193
Past service credita		(17	)		–		–
Total operating expense		624			521		494
Net interest expense on pensions deficit included in specific items (note 8)		218			209		221
Total recognised in the income statement		842			730		715

^a Past service credit primarily relates to pension plans operating outside the UK which were closed to future accrual during the year.

Group statement of comprehensive income

Remeasurements of the net pension obligation are recognised in full in the group statement of comprehensive income in the year in which they arise. These comprise the impact on the defined benefit obligation of changes in demographic and financial assumptions compared with the start of the year, actual experience being different to those assumptions and the return on plan assets being above or below the amount included in the net pension interest expense.

Group balance sheet

The net pension obligation in respect of defined benefit plans reported in the group balance sheet is set out below.

	2018								2017
At 31 March	Assets £m		Present value of liabilities £m			Deficit £m			Assets £m		Present value of liabilities £m			Deficit £m
BTPS		49,894		(55,783	)		(5,889	)		50,090		(58,649	)		(8,559	)
EEPS		763		(920	)		(157	)		748		(973	)		(225	)
Other plansa		299		(624	)		(325	)		274		(578	)		(304	)
Retirement benefit obligation		50,956		(57,327	)		(6,371	)		51,112		(60,200	)		(9,088	)
Adjustments due to effect of asset ceiling (IFRIC 14)							–								–
Deferred tax asset							1,081								1,535
Net pension obligation							(5,290	)							(7,553	)

^aIncluded in the present value of obligations of other plans is £97m (2016/17: £104m) related to unfunded pension arrangements.

Included within trade and other payables in the group balance sheet is £17m (2016/17: £15m) in respect of contributions payable to defined contribution plans.

What is IFRIC 14 and how does it impact BT?

For some pension schemes, IFRIC 14 potentially:

–  limits the amount of accounting surplus in a pension scheme that can be recognised as an asset on the balance sheet; and/or

–  requires additional pension liabilities to be recognised where scheduled future deficit contributions are greater than the unadjusted accounting deficit.

BT is not required to limit any pensions surplus or recognise additional pensions liabilities in individual plans as economic benefits are available in the form of either future refunds or reductions to future contributions.

This is on the basis that paragraph 11(b) of IFRIC 14 applies enabling a refund of surplus following the gradual settlement of the liabilities over time until there are no members remaning in the scheme.

Movements in defined benefit plan assets and liabilities

The table below shows the movements on the pension assets and liabilities and shows where they are reflected in the financial statements.

	Assets £m			Liabilities £m			Deficit £m
At 31 March 2016		43,968			(50,350	)		(6,382	)
Service cost (including administration expenses and PPF levy)		(44	)		(237	)		(281	)
Interest on pension deficit		1,413			(1,622	)		(209	)
Included in the group income statement								(490	)
Return on plan assets above the amount included in the group income statement		7,475			–			7,475
Actuarial loss arising from changes in financial assumptionsa		–			(10,221	)		(10,221	)
Actuarial loss arising from changes in demographic assumptionsa		–			(206	)		(206	)
Actuarial gain arising from experience adjustmentsb		–			163			163
Included in the group statement of comprehensive income								(2,789	)
Regular contributions by employer		313			–			313
Deficit contributions by employer		274			–			274
Included in the group cash flow statement								587
Contributions by employees		8			(8	)		–
Benefits paid		(2,315	)		2,315			–
Foreign exchange		20			(34	)		(14	)
Other movements								(14	)
At 31 March 2017		51,112			(60,200	)		(9,088	)
Service cost (including administration expenses and PPF levy)		(67	)		(309	)		(376	)
Past service credit		–			17			17
Interest on pension deficit		1,201			(1,419	)		(218	)
Included in the group income statement								(577	)
Return on plan assets above the amount included in the group income statement		10			–			10
Actuarial gain arising from changes in financial assumptionsa		–			2,251			2,251
Actuarial loss arising from changes in demographic assumptionsa		–			(221	)		(221	)
Actuarial gain arising from experience adjustmentsb		–			120			120
Included in the group statement of comprehensive income								2,160
Regular contributions by employer		264			–			264
Deficit contributions by employer		872			–			872
Included in the group cash flow statement								1,136
Contributions by employees		2			(2	)		–
Benefits paid		(2,449	)		2,449			–
Foreign exchange		11			(13	)		(2	)
Other movements								(2	)
At 31 March 2018		50,956			(57,327	)		(6,371	)

^aThe actuarial gain or loss arises from changes in the assumptions used to value the defined benefit liabilities at the end of the year compared with the assumptions used at the start of the year. This includes both financial assumptions, which are based on market conditions at the year end, and demographic assumptions such as life expectancy.

^bThe actuarial loss or gain arising from experience adjustments on defined benefit liabilities represents the impact on the liabilities of differences between actual experience during the year compared with the assumptions made at the start of the year. Such differences might arise, for example, from members choosing different benefit options at retirement, actual salary increases being different from those assumed or actual benefit increases being different to the pension increase assumption.

How do we value our retirement benefit plans?

Valuation methodology

The IAS 19 liabilities are measured as the present value of the estimated future benefit cash flows to be paid by each scheme, calculated using the projected unit credit method. These calculations are performed for the group by professionally qualified independent actuaries.

The expected future benefit payments are based on a number of assumptions including future inflation, retirement ages, benefit options chosen and life expectancy and are therefore inherently uncertain. Actual benefit payments in a given year may be higher or lower, for example if members retire sooner or later than assumed, or take a greater or lesser cash lump sum at retirement than assumed.

What are our critical judgements, estimates and assumptions?

The accounting cost of these benefits and the present value of our pension liabilities involve judgements about uncertain events including the life expectancy of the members, the salary progression of our current employees, price inflation and the discount rate used to calculate the net present value of the future pension payments. We use estimates for all of these uncertain events in determining the pension costs and liabilities in our financial statements. Our assumptions reflect historical experience, external advice and our judgement regarding future expectations.

The fair value of some of our pension assets are made up of quoted and unquoted investments. The latter require more judgement as their values are not directly observable. The assumptions used in valuing unquoted investments are affected by current market conditions and trends which could result in changes in fair value after the measurement date.

How do we value the assets?

Under IAS 19, plan assets must be valued at the bid market value at the balance sheet date. For the main asset categories:

–  Equities listed on recognised stock exchanges are valued at closing bid prices.

–  Properties are valued on the basis of open market value.

–  Bonds are measured using a combination of broker quotes and pricing models making assumptions for credit risk, market risk and market yield curves.

–  Holdings in investment funds are valued at fair value which is typically the Net Asset Value provided by the investment manager.

–  Certain unlisted investments are valued using a model based valuation such as a discounted cash flow.

–  The value of the longevity insurance contract held by the BTPS is measured by discounting the projected cash flows payable under the contract (projected by an actuary, consistent with the terms of the contract).

Review of pension benefits

Following consultation with employees and the relevant unions, we announced a number of key changes to our main UK pension arrangements in March 2018:

–  An increase to BT’s standard maximum contribution rate to 10% for employees building up benefits in the BTRSS, taking effect from 1 June 2018.

–  The closure of Sections B and C of the BTPS (representing over 99% of the BTPS active membership) to future benefit accrual, with the employees impacted by the change able to join the BTRSS for future pension provision, taking effect from 30 June 2018.

–  All employees impacted by the closure of the BTPS will receive transition payments into their BTRSS account for a period, as well as having a higher maximum BT contribution rate of 11% for a temporary period. The transition payments are 2% of pensionable salary for a period depending on the employee’s age.

–  We will establish a new ‘hybrid’ pension arrangement over the coming year for non-management employees in the BTPS at closure. This new arrangement will combine elements of both defined benefit and defined contribution pension arrangements and support those employees on lower pay scales, giving them another option for their retirement savings. We are aiming to have this in place by no later than 1 April 2019.

These changes keep our pensions fair, flexible and affordable across BT in the UK.

Overview and governance of the BTPS

What is the profile of the BTPS?

At 31 March 2018 there were 293,000 members of the BTPS. Members belong to one of three sections depending upon the date they first joined the BTPS. The membership is analysed below.

Analysis of BTPS

	Active members		Deferred members		Pensioners		Total
Sections A and B liabilities (£bn)a		4.9		4.3		29.6		38.8
Section C liabilities (£bn)		7.7		5.7		3.6		17.0
Total IAS 19 liabilities (£bn)		12.6		10.0		33.2		55.8
Total number of members		30,000		60,500		202,500		293,000

^aSections A and B have been aggregated in this table as Section A members have typically elected to take Section B benefits at retirement.

The estimated duration of the BTPS liabilities, which is an indicator of the weighted average term of the liabilities, is around 16 years although the benefits payable by the BTPS are expected to be paid over more than 70 years. Whilst benefit payments are expected to increase over the earlier years, the value of the liabilities is expected to reduce.

The chart below illustrates the estimated benefits payable from the BTPS forecast using the IAS 19 assumptions.

^aBased on accrued benefits to 30 June 2017.

What are the benefits under the BTPS?

Benefits earned for pensionable service prior to 1 April 2009 are based upon a member’s final salary and a normal pensionable age of 60.

Between 1 April 2009 and 30 June 2018, Section B and C active members accrue benefits based upon a career average re-valued earnings (CARE) basis and a normal pensionable age of 65. On a CARE basis benefits are built up based upon earnings in each year and the benefit accrued for each year is increased by the lower of inflation or the individual’s actual pay increase in each year to retirement.

Under the Scheme rules the determination of the rate of inflation for statutory minimum rates of revaluation and indexation for the majority of benefits is based upon either the Retail Prices Index (RPI) or the Consumer Prices Index (CPI) which apply to each category of member as shown below.

	Active members	Deferred members	Pensioners
SectionBa	Benefitsaccrueon a CAREbasisincreasing at thelowerof RPIor theindividual’sactual pensionable pay increase	Preservedbenefitsare revaluedbefore retirementbaseduponCPI	Increasesinbenefitsinpaymentare currentlybaseduponCPI
SectionC			Increasesinbenefitsinpaymentare currentlybaseduponRPIuptoa maximumof5%

^a Section A members have typically elected to take Section B benefits at retirement.

In December 2017, we sought a decision from the High Court as to whether it would be possible to change the index used to calculate pension increases paid in the future to members of Section C of the BTPS from RPI to another index.

In its judgment handed down on 19 January 2018, the High Court decided that it is currently not possible to change from RPI to another index. BT was then granted permission to appeal the decision to the Court of Appeal. The Court of Appeal hearing is due to take place in October 2018.

How is the BTPS governed and managed?

BT Pension Scheme Trustees Limited (the Trustee) has been appointed by BT as an independent trustee to administer and manage the BTPS on behalf of the members in accordance with the terms of the BTPS Trust Deed and Rules and relevant legislation (principally the Pension Schemes Act 1993, the Pensions Act 1995 and the Pensions Act 2004).

Under the terms of the Trust Deed there are nine Trustee directors, all of whom are appointed by BT, as illustrated below. Trustee directors are usually appointed for a three-year term but are then eligible for re-appointment.

BTPS assets

Asset allocation

The allocation of assets between different classes of investment is reviewed regularly and is a key factor in the Trustee’s investment policy. The allocations reflect the Trustee’s views on the appropriate balance to be struck between seeking returns and incurring risk, and on the extent to which the assets should be allocated to match liabilities. Current market conditions and trends are regularly assessed which may lead to adjustments in the asset allocation.

The fair value of the assets of the BTPS analysed by asset category are shown below. These are subdivided by assets that have a quoted market price in an active market and those that do not (such as investment funds).

		2018a									2017a
		Total assets £bn			of which quoted     £bn		b	Total %			Total assets £bn			of which quoted £bn		b	Total %
Growth
Equities	UK		0.5			0.5			1			0.7			0.6			2
	Overseas developed		7.8			7.3			16			9.1			8.6			18
	Emerging markets		0.5			0.4			1			0.5			0.1			1
Private Equity			1.9			–			4			1.9			–			4
Property	UK		3.9			–			8			4.1			–			8
	Overseas		1.2			–			2			1.7			–			3
Other growth assets	Absolute Return fundsc		1.5			–			3			2.3			–			5
	Non Core Creditd		3.4			1.0			7			3.5			1.1			7
	Mature Infrastructure		1.4			–			3			1.7			–			3
Liability matching
Government bonds	UK Index Linked		12.5			12.5			25			12.3			12.0			25
Investment grade credit	Global		10.0			8.0			20			7.6			5.9			15
Cash, derivatives and other
Cash balances			3.8			–			7			1.7			–			3
Longevity insurance contracte			(0.4	)		–			(1	)		(0.3	)		–			(1	)
Other non-physical cashf			1.9			–			4			3.3			–			7
Total			49.9			29.7			100			50.1			28.3			100

^a At 31 March 2018, the Scheme’s assets included equity issued by the group of £3m (2016/17: £nil) . The Scheme also held £10m (2016/17: £10m) of index-linked bonds issued by the group.

^bAssets with a quoted price in an active market.

^cThis allocation seeks to generate returns irrespective of the direction of markets. Managers within this allocation will typically manage their portfoilios without close regard to a specific market benchmark.

^dThis allocation includes a range of credit investments, including emerging market, sub-investment grade and unrated credit. The allocation seeks to exploit investment opportunities within credit markets using the expertise of a range of specialist investment managers.

^eThe Trustee has hedged some of the Scheme’s longevity risk through a longevity insurance contract which was entered into in 2014. The value reflects experience to date on the contract from higher than expected deaths. This amount partly offsets a reduction recognised in the Scheme’s liabilities.

^f Non-physical cash includes offsets in future positions and cash collateral posted in relation to derivatives held by the Scheme.

IAS 19 assumptions

The table below summarises the approach used to set the key IAS 19 assumptions for the BTPS.

	Approachtosetthe assumption
Discountrate	IAS 19 requires that the discount rate is determined by reference to market yields at the reporting date on high quality corporate bonds. The currency and term of these should be consistent with the currency and estimated term of the pension obligations. The assumption is calculated by applying the projected BTPS benefit cash flows to a corporate bond yield curve constructed based on the yield on AA-rated corporate bonds. In setting the yield curve, judgement is required on the selection of appropriate bonds to be included in the universe and the approach used to then derive the yield curve. At 31 March 2018, the discount rate model used to select bonds and derive the yield curve was updated to better reflect yields on corporate bonds over the life of the Scheme. A key difference is that the revised model excludes bonds which have either an implicit or explicit Government guarantee, which is more consistent with the requirements of IAS19, and reflects developing practice. Both the old and revised models are standard models developed by our external actuary. The impact of this change is a £2.1bn reduction in the BTPS liabilities.
RPIinflation	The RPI inflation assumption is set using the entire inflation curve, weighted by projected BTPS benefit cash flows, and making an adjustment for an inflation risk premium (to reflect the extra premium paid by investors for inflation protection), which is currently assumed to be 20bps.
CPIinflation	CPIisassessedata marginbelowRPItakingintoaccountmarketforecastsandindependentestimatesoftheexpected difference.
Salaryincreases	Long-termsalaryincreasesforBTPSmembersareassumedtobeequaltoCPIinflation.
Pensionincreases	Benefitsareassumedtoincreasein linewiththeRPIorCPIinflationassumptions,basedontherelevantindexfor increasingbenefits,asprescribedbytherulesoftheBTPSandsummarisedabove.
Longevity	The longevity assumption has been updated to take into account: –  the actual mortality experience of the BTPS pensioners, based on a formal review conducted at the 2014 triennial funding valuation –  future improvements in longevity based on a model published by UK actuarial profession’s Continuous Mortality Investigation (using the CMI 2016 Mortality Projections model with a 1.25% per year long-term improvement parameter).

Thekey financial assumptionsused tomeasure theliabilitiesof the BTPSare shown below.

	Nominal rates (per year)									Real rates (per year)a
At 31 March	2018 %			2017 %			2016 %			2018 %			2017 %			2016 %
Rate used to discount liabilities		2.65			2.40			3.30			(0.44)			(0.78)			0.44
Inflation – increase in RPI		3.10			3.20			2.85		–				–			–
Inflation – increase in CPI	2.00		b	2.00		c	1.65		d	(1.1)		b	(1.2)		c	(1.2)		d

^aThe real rate is calculated relative to RPI inflation.

^bAssumed to be 0.1% higher until 31 March 2023.

^cAssumed to be 0.5% higher until 31 March 2019.

^dAssumed to be 0.2% higher until 31 March 2017.

TheBTPSrepresentsover 97% ofthegroup’sretirementbenefitobligation. While thefinancial assumptions may vary foreach plan,the nominal financial assumptionsweighted byliabilities acrossall plansare equal tothefiguresshown in the table above (tothenearest 0.05%).

Basedon the IAS19 longevity assumptions,theforecast life expectanciesfor BTPSmembersaged 60 are as follows:

At 31 March	2018 Number of years		2017 Number of years
Male in lower pay bracket		25.8		26.2
Male in medium pay bracket		27.1		27.5
Male in higher pay bracket		28.5		28.9
Female in lower pay bracket		28.5		28.9
Female in higher pay bracket		28.7		29.2
Average improvement for a member retiring at age 60 in 10 years' time		0.7		1.0

Risks underlyingtheassumptions

Background

The BTPSfacessimilarriskstoother UK DB schemes:things likefuture low investmentreturns, highinflation, longerlife expectancyand regulatory changes may all mean theBTPSbecomes more ofa financial burden.Furtherdetails are set outon page 41.

Changes in externalfactors,such as interestrates,can have an impacton the IAS19 assumptions,impactingthemeasurement of BTPS liabilities. Thesefactorscan alsoimpact the Scheme assets.The BTPShedgessome of theserisks, includinglongevityandcurrency using financial instrumentsand insurance contracts.

Someofthe key financial risks, and mitigations, forthe BTPSare setout inthetablebelow.

Changesinbondyields	Afallin yieldsonAA-ratedcorporatebonds,usedto settheIAS19discountrate,willleadtoanincreasein the IAS19liabilities. TheBTPS’sassetsincludecorporatebonds,governmentbondsandinterestratederivativeswhichareexpected topartlyoffsettheimpactofmovementsinthediscountrate.However,yieldsontheseassetsmaydiverge comparedwiththediscountrateinsomescenarios.
Changesininflation expectations	AsignificantproportionofthebenefitspaidtomembersarecurrentlyincreasedinlinewithRPIor CPIinflation.An increaseinlong-terminflationexpectationswill leadtoanincreaseintheIAS19liabilities. TheBTPS’sassetsincludeindex-linkedgovernmentbondsandinflationderivativeswhichareexpectedtopartly offsettheimpactofmovementsin inflationexpectations.
Changesinlifeexpectancy	Anincreaseinthelifeexpectancyof memberswillresultinbenefitsbeingpaidoutforlonger,leadingto an increaseintheBTPSliabilities. TheBTPSholdsalongevityinsurancecontractwhichcoversaround25%oftheBTPS’stotalexposureto improvementsinlongevity,providinglong-termprotectionandincometothe BTPSin theeventthatmemberslive longerthancurrentlyexpected.

Otherrisksincludevolatileasset returns (ie whereassetreturns differ from the discountrate)andchanges in legislation or regulation whichimpact the value of the liabilities or value ofthe assets.

Quantification

BT’sindependent actuaryhas assessed thepotential negative impactof thekeyrisksthatmight occurno more than once in every 20 years illustrated as the following three scenarios:

Scenario	1-in-20 events
	2018		2017
1. Fall in discount ratea		1.10%		1.00%
2. Increase to inflation rateb		0.70%		0.90%
3. Increase to life expectancy		1.35 years		1.35 years

^aScenario assumes a fall in the yields on both government and corporate bonds.

^bAssuming RPI, CPI, pension increases and salary increases all increase by the same amount.

Theimpactshownunder each scenario looks at each event in isolation– in practice a combination of eventscouldarise.

Thesensitivityof the deficit allowsforboththechange in the liabilities and the assumed change in theassets.Forexample,theincrease in the deficit under the life expectancyscenario incorporates theexpected movementin thevalue of the insurance contractheld to hedge longevity risk.

Thesensitivitieshave beenprepared using a similar approach as2016/17 which involves calculating theliabilities and deficitusing the alternativeassumptionsstated.

BTPSfunding

Triennialfundingvaluation

Thetriennial valuation is carried out fortheTrusteebya professionallyqualified independent actuary.The purpose of the valuationis to design a funding plan toensure thatthe BTPShassufficientfunds availabletomeetfuturebenefitpayments.Thelatestfundingvaluation was performedasat 30 June2017.Thenextfunding valuation will have an effective date of no laterthan30 June 2020.

Thevaluation methodologyforfunding purposes,which isbased on prudent assumptions,is broadly as follows:

–  Assetsare valued atmarket value atthevaluation date.

–  Liabilities aremeasured on an actuarialfunding basis using theprojectedunitcredit method and discountedtotheirpresent value.

Theresults of the two mostrecenttriennial valuations are shown below.

	June 2017 valuation £bn	June 2014 valuation £bn
BTPS liabilities	(60.4)		(47.2	)
Market value of BTPS assets	49.1	40.2
Funding deficit	(11.3)		(7.0	)
Percentage of accrued benefits covered by BTPS assets at the valuation date	81.3%	85.2%
Percentage of accrued benefits on a solvency basis covered by the BTPS assets at the valuation date	62.2%	63.0%

Between June 2014 and June 2017, the Scheme benefited from asset returns of 10.5% a year, that were higher than assumed under the 2014 funding assumptions, and £2.0bn of deficit contributions. The fall in long-term real interest rates resulted in an increase in liabilities, which has more than offset the improvements in the Scheme’s assets. There has been a reduction in the liabilities as a result of allowing for slower improvements to life expectancy being forecast by actuaries. This impact has been broadly offset by the impact of changes to the investment strategy that have reduced the current and future level of investment risk in the Scheme.

Key assumptions– fundingvaluation

Thesevaluations were determinedusing thefollowingprudentlong-term assumptions.

	Nominal rates (per year)		Real rates (per year)a
	June 2017 valuation %	June 2014 valuation %	June 2017 valuation %	June 2014 valuation %
Average single equivalent discount rate	2.6	4.5	(0.8)		1.0
Average long-term increase in RPI	3.4	3.5	–	–
Average long-term increase in CPI	2.4	2.5	(1.0)		(1.0	)

a Therealrateiscalculatedrelativeto RPIinflationandisshownasa comparator.

Thediscount rate at 30 June 2017 was derived fromprudent return expectationsabove a risk-free yield curve based on gilt and swaprates.The discount rate reflects views offuturereturnsat the valuationdate, allowing for the Scheme to hold 45% of its investments in growth assets initially, before de-risking to a low risk investment approach by 2034. Thisgives a prudentdiscount rate of1.4% per year abovetheyield curve initially,trending down to0.7% peryear above the curvein the long-term.Theassumption is equivalent tousing a flatdiscount rate of1.0% per year above the yield curve.

At the 2014 valuation, the funding approach assumed the Scheme would hold 60% of its investments in growth assets (such as equities and property) for a period, before de-risking to a low-risk investment approach by 2034.

Theaverage lifeexpectancyassumptions atthevaluation dates,formembers60 yearsof age,are asfollows.

Number of years from valuation date	June 2017 assumptions	June 2014 assumptions
Male in lower pay bracket	25.9	26.1
Male in medium pay bracket	27.2	27.5
Male in high pay bracket	28.6	29.0
Female in lower pay bracket	28.6	28.9
Female in high pay bracket	28.9	29.2
Average improvement for a member retiring at age 60 in 10 years’ time	0.9	1.3

Payments made to the BTPS

Year ended 31 March	2018 £m		2017 £m
Ordinary contributions		248	303
Deficit contributions		850	250
Total contributions in the year		1,098		553

Futurefundingobligationsandrecoveryplan

Under theterms ofthe Trust Deed, the group isrequired tohave a funding plan, determinedattheconclusion of the triennialfunding valuation, which isa legal agreement between BTand the Trusteeand should addressthe deficit over a maximumperiod of20 years.

In May 2018,the2017 triennial funding valuation wasfinalised, agreed withtheTrusteeand certifiedby theScheme Actuary.The fundingdeficit at30 June 2017 was £11.3bn. The deficit will be met over a 13-year period, maintaining the remaining period of the previous plan.

The deficit contributions have three components:

–  Payments by BT over the three years to 31 March 2020 totalling £2.1bn. This is equal to the amount due over the same period under the previous recovery plan. £850m of this was paid in March 2018 and the remaining £1,250m is to be paid by 30 June 2019.

–  A further £2.0bn contribution, due to be funded from the proceeds of the issuance of bonds, which will be held by the BTPS. The bonds will be:

– issued as soon as practicable under BT’s Euro Medium Term Note Programme

– sterling denominated and have maturities ranging from 2033to 2042

– £1.0bn fixed interest and £1.0bn CPI-linked.

–  For the 10 years from 1 April 2020 to 31 March 2030, BT will make annual payments of around £900m, typicaly by 31 March each year.

– £400m of BT’s contribution in the financial year 2020/21 will be made by 30 June 2020.

This means that the recovery plan includes material contributions by BT to the Scheme of £4.5bn by 30 June 2020, when the next valuation is expected to take place.

  BTis scheduled tomake future deficit payments to the BTPSin line withthetable below.  

Year to 31 March	2018	2019		2020		2021		2022		2023	2024	2025	2026	2027	2028	2029	2030
Deficit contribution (£m)	850	2,000	a	1,250	b	900	c	900	d	907	907	907	907	907	907	907	907

^a due to be paid shortly, but no later than 30 June 2019.

^bpayable by 30 June 2019.

^c£400m payable by 30 June 2020.

^d£200m payable by 30 June 2021.

Basedon the 2017 fundingvaluation agreement,the group expectstomake contributionsof approximately £2,075m totheBTPSin 2018/19,comprising ordinary contributions of approximately £75mand deficit contributions of£2,000m.The reduction in the level of ordinary contributions primarily reflects the closure of the BTPS to Section B and C members, which is currently intended to take place on 30 June 2018. In addition, contributions towards the cost of administering the Scheme, PPF levies and providing future benefits for the remaining members will continue to be made after this date.

Otherprotections

The2017 funding agreement with the Trusteeincluded additional featuresforBTtoprovide support totheBTPS.Theseinclude:

Feature	Detail
Shareholder distributions	BT will provide additional payments to the BTPS by the amount that shareholder distributions exceed a threshold.The thresholdallows for10% per year dividend persharegrowthplus£200mper yearofshare buybacks on a cumulative basis. This willapplyuntil 30 June 2021, or until the finalisationofthe nextvaluation if earlier. BTwill also consult with theTrustee ifitconsiders sharebuybacks inexcess of £200m peryear or making a special dividend. This obligation is on-going until otherwise terminated.
Material corporateevents	Inthe event that BTgenerates netcash proceeds greaterthan£1.0bn fromdisposals(netof acquisitions)in any12-month period ending 30 June, BTwill make additional contributions to theBTPSequal toonethirdofthosenet cash proceeds. This obligation applies until the next valuation is signed. BTwill consult with the Trustee if:   –  itconsiders making acquisitions with a total costof more than £1.0bn in any12-month period; or   –  itconsiders making disposalsof more than£1.0bn; or   –  it considers making a Class 1 transaction (acquisition or disposal); or   –  it is subjecttoa takeover offer. This obligation is on-going until otherwise terminated. BTwill advise the Trusteeshould there be other material corporate eventswhich would materiallyimpactBT’s covenant tothe BTPS. This obligation is on-going until otherwise terminated.
Negative pledge	A negative pledge that future creditors will not be granted superior security to the BTPS in excess of a £1.5bn threshold, to cover both British Telecommunications plc and BT Group plc. This provision applies until the deficit reduces to below £2.0bn at any subsequent funding valuation.

Inthe highly unlikely event thatthegroup were to become insolvent thereareadditional protections ofBTPSmembers’ benefits:

Feature	Detail
Crown Guarantee	The Crown Guarantee was granted by the Government when the group was privatised in 1984 and would only come into effect upon the insolvency of BT. The Trustee brought court proceedings to clarify the scope and extent of the Crown Guarantee. The Court of Appeal judgment on 16 July 2014 established that: –  the Crown Guarantee covers BT’s funding obligation in relation to the benefits of members of the BTPS who joined post-privatisation as well as those who joined pre-privatisation (subject to certain exceptions) –  the funding obligation to which the Crown Guarantee relates is measured with reference to BT’s obligation to pay deficit contributions under the rules of the BTPS. The Crown Guarantee is not taken into account for the purposes of the actuarial valuation of the BTPS and is an entirely separate matter, only being relevant in the highly unlikely event that BT became insolvent.
Pension ProtectionFund (PPF)	The Pension Protection Fund (PPF) may take over the BTPS and pay benefits not covered by the Crown Guarantee to members. There are limits on the amounts paid by the PPF and the PPF would not provide exactly the same benefits as those provided under the BTPS Rules.

Otherbenefitplans

Inaddition tothe BTPS,thegroup maintains benefitplans around theworld witha focuson these beingappropriate forthelocal market and culture.

EEPensionScheme(EEPS)

The EEPSisthe second largest defined benefit plan sponsoredbythe group withdefined benefit liabilities ofaround £0.9bn.The EEPS also has a defined contribution section with around 11,500 active members.

At 31 March 2018, the definedbenefitsection’s assetsare investedacrossa number ofassetclassesincluding global equities (28%),property and illiquid alternatives(22%), an absolute returnportfolio(25%) and a liability driven investment portfolio(25%).

Thetriennial valuation ofthedefined benefitsection was performedasat 31December2015,and agreed in March 2017. Thisshoweda fundingdeficit of£141m. Thegroup is scheduled to contribute £1.875m each month between 1 April 2018 and November 2020.

Thenext fundingvaluation will have an effective dateofno laterthan 31 December 2018.

BTRSS

TheBTRSSisthe largestdefined contribution scheme maintained by thegroup witharound 35,000 active members.Inthe year to31 March 2018,thegroup contributed£167mtothe BTRSS.

Other schemes

BT operates a number of overseas pension schemes. In December 2017, BT closed two defined benefit plans which operate in the Netherlands. This resulted in a c£14m past service credit arising from the change in future indexation obligations. A further £3m past service credit was recognised in 2017/18 relating to various other pension plans operating outside the UK.

Summary of Retirement Benefit Plan

	Whatarethey?	Howdothey impact BT’sfinancialstatements?
Definedcontributionplans	Benefitsina definedcontributionplan arelinkedto: –  contributionspaid –  theperformanceofeachindividual’s choseninvestments –  theforminwhichindividualschoose totaketheirbenefits. Contributionsarepaidintoan independentlyadministeredfund.	Theincomestatementchargeinrespectof definedcontributionplans representsthecontributionpayablebythegroupbaseduponafixed percentageofemployees’pay. Thegrouphasnoexposuretoinvestmentandotherexperiencerisks.
Definedbenefitplans	Benefitsina definedbenefitplanare: –  determinedbytheplanrules, dependentonfactorssuchasage, yearsofserviceandpensionable pay –  notdependentuponactual contributionsmadebythecompany ormembers.	Theincomestatementservicecost inrespectofdefinedbenefitplans representstheincreaseinthedefinedbenefitliabilityarisingfrompension benefitsearnedbyactivemembersinthecurrentperiod. Thegroupisexposedtoinvestmentandotherexperiencerisksandmayneed tomakeadditionalcontributionswhereit isestimatedthatthebenefitswillnot bemetfromregularcontributions,expectedinvestmentincomeandassets held.

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Share-based payments

12 Months Ended

Mar. 31, 2018

Text Block1 [Abstract]

Share-based payments

20. Share-based payments

What share incentive arrangements do we have?

Our plans include savings-related share option plans for employees and those of participating subsidiaries, further share option plans for selected employees and a stock purchase plan for employees in the US. We also have several share plans for executives. All share-based payment plans are equity-settled. Details of these plans and an analysis of the total charge by type of award is set out below.

Year ended 31 March	2018 £m	2017 £m	2016 £m
Employee Saveshare Plans	42	40	27
Executive Share Plans:
Incentive Share Plan (ISP)	16	–	21
Deferred Bonus Plan (DBP)	4	9	4
Retention Share Plan (RSP)a	21	8	1
Other plans	1	–	5
	84	57	58

^a Re-presented to show RSPs separately from other plans.

Employee Saveshare Plans

Under an HMRC-approved savings-related share option plan, employees save on a monthly basis, over a three or five-year period, towards the purchase of shares of BT Group plc at a fixed price determined when the option is granted. This price is usually set at a 20% discount to the market price for five-year plans and 10% for three-year plans. The options must be exercised within six months of maturity of the savings contract, otherwise they lapse. Similar plans operate for our overseas employees.

Incentive Share Plan (ISP)

Under the ISP, participants are only entitled to these shares of BT Group plc in full at the end of a three-year period if BT Group plc has met the relevant pre-determined corporate performance measures and if the participants are still employed by the group. For ISP awards granted in 2017/18, 2016/17 and 2015/16: 40% of each award is linked to a total shareholder return (TSR) target for a comparator group of companies from the beginning of the relevant performance period; 40% is linked to a three-year cumulative normalised free cash flow measure; and 20% to growth in underlying revenue excluding transit.

Deferred Bonus Plan (DBP)

Under the DBP, awards are granted annually to selected employees. Shares in BT Group plc are transferred to participants at the end of three years if they continue to be employed by the group throughout that period.

Retention Share Plan (RSP)

Under the RSP, awards are granted to selected employees. Shares of BT Group plc are transferred to participants at the end of a specified retention period if they continue to be employed by the group throughout that period.

Under the terms of the ISP, DBP and RSP, dividends or dividend equivalents earned on shares of BT Group plc during the conditional periods are reinvested in company shares for the potential benefit of the participants.

Employee Saveshare Plans

Movements in Employee Saveshare options are shown below.

	Movement in the number of share options									Weighted average exercise price
Year ended 31 March	2018 millions			2017 millions			2016 millions			2018 pence		2017 pence	2016 pence
Outstanding at 1 April		189		197			226				313	287	226
Granted		69		44			47				250	362	385
Forfeited		(41	)		(18	)		(12	)		328	345	306
Exercised		(30	)		(33	)		(63	)		169	208	139
Expired		(12	)		(1	)		(1	)		353	345	247
Outstanding at 31 March		175		189			197				306	313	287
Exercisable at 31 March	–			–			–				320	237	140

The weighted average share price for all options exercised during 2017/18 was 311p (2016/17: 357p, 2015/16: 463p).

The following table summarises information relating to options outstanding and exercisable under Employee Saveshare plans at 31 March 2018.

Normal dates of vesting and exercise (based on calendar years)	Exercise price per share	Weighted average exercise price			Number of outstanding options millions		Weighted average remaining contractual life
2018	249p – 423p		306	p		25	10 months
2019	319p – 397p		333	p		53	22 months
2020	243p – 376p		307	p		44	34 months
2021	353p		353	p		17	46 months
2022	243p		243	p		36	58 months
Total			306	p		175	33 months

Executive share plans

Movements in executive share plan awards during 2017/18 are shown below:

	Number of shares (millions)
	ISP			DBP			RSP			Total
At 1 April 2017		45			7			4			56
Awards granted		26			2			10			38
Awards vested		–			(3	)		(2	)		(5	)
Awards lapsed		(20	)		–			(1	)		(21	)
Dividend shares reinvested		3			–			1			4
At 31 March 2018		54			6			12			72

Fair values

The following table summarises the fair values and key assumptions used for valuing grants made under the Employee Saveshare plans and ISP in 2017/18, 2016/17 and 2015/16.

			2018			2017		2016
Year ended 31 March	Employee Saveshare		ISP		Employee Saveshare	ISP	Employee Saveshare	ISP
Weighted average fair value		56p		202p	72p	328p	81p	364p
Weighted average share price		296p		281p	422p	426p	454p	451p
Weighted average exercise price		250p	n/a		362p	n/a	385p	n/a
Expected dividend yield	3.12% – 3.21%		n/a		2.9% – 3.4%	n/a	3.2% –3.7%	n/a
Risk free rates	0.1% – 0.2%			0.2%	0.5% – 0.8%	0.6%	0.7% – 1.6%	0.7%
Expected volatility	23.1% – 24.3%			23.6%	19.0% – 21.5%	21.8%	19.7% –22.7%	22.0%

Employee Saveshare grants are valued using a Binomial options pricing model. Awards under the ISP are valued using Monte Carlo simulations. TSRs are generated for BT and the comparator group at the end of the three-year performance period, using each company’s volatility and the cross correlation between pairs of stocks.

Volatility has been determined by reference to BT Group plc’s historical volatility which is expected to reflect the BT Group plc’s share price in the future. An expected life of three months after vesting date is assumed for Employee Saveshare options. For all other awards the expected life is equal to the vesting period. The risk-free interest rate is based on the UK gilt curve in effect at the time of the grant, for the expected life of the option or award.

The fair values for the DBP and RSP were determined using the market price of the shares at the grant date. The weighted average share price for DBP awards granted in 2017/18 was 282p (2016/17: 421p, 2015/16: 451p) and for RSP awards granted in 2017/18 it was 282p (2016/17: 417p, 2015/16: 420p).

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Investments

12 Months Ended

Mar. 31, 2018

Disclosure Of Investments [Abstract]

Investments

21. Investments

At 31 March	2018 £m		2017 £m		2016 £m
Non-current assets
Available-for-sale		46		37		39
Amounts owed by ultimate parent company		2,983		1,371		1,409
Amounts owed by parent company		10,318		10,191		10,510
Fair value through profit or loss		7		7		7
		13,354		11,606		11,965
Current assets
Available-for-sale		2,575		1,437		2,878
Amounts owed by ultimate parent company		34		28		26
Amounts owed by parent company		168		192		327
Loans and receivables		447		83		40
		3,224		1,740		3,271

Loansandreceivablesareheldonthebalancesheetatamortisedcostandthisapproximates fairvalue.Loansandreceivablesconsist ofinvestmentsintermdepositsdenominatedinSterling of£416m (2016/17:£35m,2015/16:£10m), inUSDollarsof£27m(2016/17: £30m, 2015/16:£30m)andinothercurrencies £4m(2016/17:£18m,2015/16: £nil).

Fair value hierarchy At 31 March 2018	Level 1 £m		Level 2 £m		Level 3 £m		Total held at fair value £m
Non-current and current investments
Available-for-sale investments		32		2,575		14		2,621
Fair value through profit or loss		7	–		–			7
Total		39		2,575		14		2,628

At 31 March 2017	Level 1 £m		Level 2 £m		Level 3 £m		Total held at fair value £m
Non-current and current investments
Available-for-sale investments		21		1,437		16		1,474
Fair value through profit or loss		7		–		–		7
Total		28		1,437		16		1,481

At 31 March 2016	Level 1 £m		Level 2 £m		Level 3 £m		Total held at fair value £m
Non-current and current investments
Available-for-sale investments		24	2,878		15		2,917
Fair value through profit or loss		7		–		–		7
Total		31		2,878		15		2,924

The three levels of valuation methodology used are:

Level 1 – uses quoted prices in active markets for identical assets or liabilities.

Level 2 – uses inputs for the asset or liability other than quoted prices, that are observable either directly or indirectly.

Level 3 – uses inputs for the asset or liability that are not based on observable market data, such as internal models or other valuation method.

Level 2 balances classified as available-for-sale consist of investments in liquidity funds denominated in Sterling of £2,180m (2016/17: £900m, 2015/16: £2,430m) and in Euros of £395m (2016/17: £537m, 2015/16: £448m). The fair value of liquidity fund is calculated by using notional currency amounts adjusted by year end spot exchange rates.

Level 3 balances consist of available-for-sale investments of £14m (2016/17: £16m,2015/16: £15m) which represent investments in a number of private companies. In the absence of specific market data, these investments are held at cost, adjusted as necessary for impairments, which approximates to fair value.

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Cash and cash equivalents

12 Months Ended

Mar. 31, 2018

Cash And Cash Equivalents [Abstract]

Cash and cash equivalents

22. Cash and cash equivalents

At 31 March	2018 £m			2017 £m			2016 £m
Cash at bank and in hand		439			467			893
Cash equivalents
Loans and receivables
US deposits		26			32			44
UK deposits		31			1			20
Other deposits		25			26			32
Total cash equivalents		82			59			96
Total cash and cash equivalents		521			526			989
Bank overdrafts (note 23)		(29	)		(17	)		(537	)
Cash and cash equivalents per the cash flow statement		492			509			452

The group’s cash and cash equivalents include restricted cash of £32m (2016/17: £43m, 2015/16: £51m), of which £29m (2016/17: £41m, 2015/16: £44m) was held in countries where local capital or exchange controls currently prevent us from accessing cash balances. The remaining balance of £3m (2016/17: £2m, 2015/16: £7m) was held in escrow accounts, or in commercial arrangements akin to escrow.

Cash equivalents are classified as loans and receivables and are held on the group balance sheet at amortised cost which equates to fair value.

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Loans and other borrowings

12 Months Ended

Mar. 31, 2018

Text Block1 [Abstract]

Loans and other borrowings

23. Loans and other borrowings

Capital management policy

The capital structure is managed by BT Group plc, the ultimate parent of the group. Its capital management policy is set out in the Report of the Directors on page 90.

The table below shows the key components of external gross debt and of the increase of £2,195m this year.

	At 1  April 2017 £m			Issuance/ (maturities) £m			Fair value movements £m			Foreign exchange £m			Transfer to within one year £m			Accrued interest movements £m		At 31 March 2018 £m
Debt due within one yeara		2,632			(1,401	)		(18	)		(95	)		1,163		–			2,281
Debt due after one year		10,081			3,760			(60	)		(440	)		(1,347	)	–			11,994
Cash flows from Derivatives related to net debt	–				(188	)	–			–				188		–		–
Overdrafts	–				4		–			–				(4	)	–		–
Impact of cross-currency swapsb		(1,419	)	–			–				545		–			–			(874	)
Removal of the accrued interest and fair value adjustmentsc		(314	)	–				78		–			–				10		(226	)
External gross debt		10,980			2,175		–				10		–				10		13,175

^aIncluding accrued interest and bank overdrafts.

^bTranslation of debt balances at swap rates where hedged by cross currency swaps.

^cRemoval of accrued interest applied to reflect the effective interest rate method and removal of fair value adjustments.

The table below gives the details of the listed bonds and other debt.

At 31 March	2018 £m		2017 £m		2016 £m
1.625% US$600m bond due June 2016a		–		–		419
8.50% £678m bond due December 2016 (minimum 7.50%b)		–		–		696
3.5% €500m bond due February 2017a		–		–		398
1.25% US$500m bond due February 2017a		–		–		348
6.625% £500m bond due June 2017a		–		526		525
5.95% US$1,100m bond due January 2018a		–		891		775
3.25% €600m bond due August 2018a		541		539		510
2.35% US$800m bond due February 2019a		572		642		558
4.38% £450m bond due March 2019		455		460		464
1.125% €1,000m bond due June 2019a		883		863		800
8.625% £300m bond due March 2020		300		300		300
0.625% €1,500m bond due March 2021a		1,309		1,282		1,190
0.5% €575m bond due June 2022a		502		–		–
1.125% €1,100m bond due March 2023a		961		942		873
1% €575m bond due June 2024a		506		–		–
1% €1,100m bond due November 2024a		959		–		–
3.50% £250m index linked bond due April 2025		419		403		396
1.75% €1,300m bond due March 2026a		1,137		1,113		1,032
1.5% €1,150m bond due June 2027a		1,009		–		–
5.75% £600m bond due December 2028		721		731		741
9.125% US$2,670m bond due December 2030a (minimum 8.625%b)		1,943		2,191		1,910
3.125% £500m bond due November 2031		502		–		–
6.375% £500m bond due June 2037a		522		522		522
3.625% £250m bond due November 2047		250		–		–
Total listed bonds		13,491		11,405		12,457
Finance leases		223		229		233
LIBOR + 0.95% £438m Syndicated loan facilities due April 2016	–		–			438
2.21% £350m bank loan due December 2017	–			352		354
Acquisition facility	–		–			181
Other loans		532		710		561
Bank overdrafts (note 22)		29		17		537
Amounts due to ultimate companyc		1,061		1,183		1,024
Total other loans and borrowings		1,622		2,262		3,095
Total loans and borrowings		15,336		13,896		15,785

^aDesignated in a cash flow hedge relationship.

^bThe interest rate payable on this bond attracts an additional 0.25% for a downgrade by one credit rating by either Moody’s or S&P to the group’s senior unsecured debt below A3/A–respectively. In addition, if Moody’s or S&P subsequently increase the ratings then the interest rate will be decreased by 0.25% for each rating category upgrade by each rating agency. In no event will the interest rate be reduced below the minimum rate reflected in the above table.

^cAmounts due to ultimate parent company are denominated in Sterling and incur a floating rate of interest based on LIBOR.

Unless previously designated in a fair value hedge relationship, all loans and other borrowings are carried on our balance sheet at amortised cost and in the table above. The fair value of listed bonds and other long-term borrowings is £14,878m (2016/17: £13,496m, 2015/16: £14,500m) and the fair value of finance leases is £253m (2016/17: £273m, 2015/16: £284m).

Thefairvalue ofourbonds and other long-termborrowings is estimated on the basisof quoted marketprices (Level 1), or based on similar issuances wherethey exist (Level 2).Thecarrying amount ofother loansand bankoverdraftsequatestofairvalue due totheshort maturityofthese items (Level 3).

Theinterestratespayable on loansand borrowings disclosedabove reflect the coupons ontheunderlyingissued loans and borrowings and not theinterestratesachieved throughapplying associated cross-currencyand interestrate swaps in hedge arrangements.

Loans and otherborrowings are analysed asfollows:

At 31 March	2018 £m		2017 £m		2016 £m
Current liabilities
Listed bonds		1,702		1,539		2,013
Finance leases		18		15		8
Bank loans	–			352		–
Syndicated loan facilities	–			–		619
Other loans and bank overdraftsa		561		726		1,096
Amounts due to ultimate parent company		17		159		20
Total current liabilities		2,298		2,791		3,756
Non-current liabilities
Listed bonds		11,789		9,866		10,444
Finance leases		205		214		225
Bank loans	–		–			354
Other loans	–			1		2
Amounts due to ultimate parent company		1,044		1,024		1,004
Total non-current liabilities		13,038		11,105		12,029
Total		15,336		13,896		15,785

^aIncludescollateralreceivedon swapsof £525m(2016/17:£702m,2015/16:£553m).

Thecarrying values disclosed intheabove table reflect balancesat amortised costadjustedforaccrued interestand fairvalue adjustments totherelevant loansorborrowings.Thesedo not reflect the final principal repaymentsthatwill arise aftertaking account of therelevant derivatives in hedgingrelationshipswhichare reflected in thetablebelow. Apart from finance leases, all borrowings as at 31 March 2018,2017 and 2016 were unsecured.

The principal repaymentsofloans and borrowingsat hedgedrates amountedto£14,219m(2016/17:£12,138m,2015/16: £14,756m)and repayments fall due asfollows:

	2018							2017							2016
At 31 March	Carrying amount £m		Effect of hedging and interest £m			Principal repayments at hedged rates £m		Carrying amount £m		Effect of hedging and interest £m			Principal repayments at hedged rates £m		Carrying amount £m		Effect of hedging and interest £m			Principal repayments at hedged rates £m
Within one year, or on demand		2,289		(308	)		1,981		2,791		(523	)		2,268		3,756		(252	)		3,504
Between one and two years		1,192		(66	)		1,126		1,614		(197	)		1,417		1,632		(216	)		1,416
Between two and three years		1,332		(154	)		1,178		1,166		(43	)		1,123		1,488		(72	)		1,416
Between three and four years		18	–				18		1,295		(121	)		1,174		1,103		18			1,121
Between four and five years		1,489		(111	)		1,378		12		–			12		1,199		(26	)		1,173
After five years		8,943		(405	)		8,538		6,868		(724	)		6,144		6,428		(302	)		6,126
Total due for repayment after more than one year		12,974		(736	)		12,238		10,955		(1,085	)		9,870		11,850		(598	)		11,252
Total repayments		15,263		(1,044	)		14,219		13,746		(1,608	)		12,138		15,606		(850	)		14,756
Fair value adjustments		73							150							179
Total loans and other borrowings		15,336							13,896							15,785

Obligationsunder finance leases are analysed asfollows:

	2018			2017			2016			2018		2017		2016
	Minimum lease payments									Repayment of outstanding lease obligations
At 31 March				£m			£m					£m		£m
Amounts payable under finance leases:
Due within one year		33			29			13			18		14		8
Between two to five years		122			102			105			71		50		51
After five years		193			237			265			130		165		174
		348			368			383			219		229		233
Less: future finance charges		(129	)		(139	)		(150	)	–		–		–
Fair value adjustments for purchase price adjustment		4		–			–				4	–		–
Total finance lease obligations		223			229			233			223		229		233

Assetsheld under finance leases mainly consist of buildings and network assets.Ourobligations underfinance leases are secured by thelessors’ title totheleased assets.

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Finance expense

12 Months Ended

Mar. 31, 2018

Disclosure Of Finance Income Expense [Abstract]

Finance expense

24. Finance expense

Year ended 31 March	2018 £m		2017 £m			2016 £m
Finance expense
Interest on:
Financial liabilities at amortised cost and associated derivatives		478		567			489
Finance leases		16		15			14
Derivatives		14		12			11
Fair value movements on derivatives not in a designated hedge relationship		1		(2	)		(5	)
Reclassification of cash flow hedge from other comprehensive income		34		(1	)		3
Unwinding of discount on provisions		15		16			8
Interest payable on ultimate parent company borrowings		18		25			20
Total finance expense before specific items		576		632			540
Specific items (note 8)		218		210			229
Total finance expense		794		842			769

Year ended 31 March	2018 £m		2017 £m		2016 £m
Finance income
Interest on available-for-sale investments		5		6		8
Interest on loans and receivables		7		7		6
Other interest and similar income	–		–			23
Interest income on loans to immediate and ultimate parent company		203		219		352
Total finance income		215		232		389
Year ended 31 March	2018 £m		2017 £m		2016 £m
Net finance expense before specific items		361		400		151
Specific items (note 8)		218		210		229
Net finance expense		579		610		380

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Financial instruments and risk management

12 Months Ended

Mar. 31, 2018

Text Block1 [Abstract]

Financial instruments and risk management

25. Financial instruments and risk management

Risk management is performed by BT Group plc, the ultimate parent company of the group.

We issue or hold financial instruments mainly to finance our operations; to finance corporate transactions such as dividends, share buybacks and acquisitions; for the temporary investment of short-term funds; and to manage currency and interest rate risks. In addition, various financial instruments, for example trade receivables and payables arise directly from operations.

How do we manage financial risk?

Our activities expose us to a variety of financial risks: market risk (including interest rate risk and foreign exchange risk), credit risk and liquidity risk.

Treasury operation

We have a centralised treasury operation whose primary role is to manage liquidity and funding requirements as well as our exposure to associated financial and market risks, including credit risk, interest rate risk and foreign exchange risk.

Treasury policy

Treasury policy is set by the BT Group plc Board. Group treasury activities are subject to a set of controls appropriate for the magnitude of borrowing, investments and group-wide exposures. The BT Group plc Board has delegated authority to operate these policies to a series of panels responsible for the management of key treasury risks and operations. Appointment to and removal from the key panels requires approval from two of the following: the chairman, the chief executive or the chief financial officer BT Group plc.

There has been no change in the nature of our risk profile between 31 March 2018 and the date of approval of these financial statements.

How do we manage interest rate risk?

Management policy

Interest rate risk arises primarily from our long-term borrowings. Interest cash flow risk arises from borrowings issued at variable rates, partially offset by cash held at variable rates. Fair value interest rate risk arises from borrowings issued at fixed rates.

Our policy, as set by the BT Group plc Board, is to ensure that at least 70% of BT Group plc’s ongoing net debt is at fixed rates. Short-term interest rate management is delegated to the treasury operation while long-term interest rate management decisions require further approval by the BT Group plc group chief financial officer, group director tax, treasury and insurance or the group treasurer who each have been delegated such authority from the BT Group plc Board.

Hedging strategy

In order to manage our interest rate profile, we have entered into cross-currency and interest rate swap agreements to vary the amounts and periods for which interest rates on borrowings are fixed. The duration of the swap agreements matches the duration of the debt instruments. The majority of the group’s long-term borrowings are subject to fixed Sterling interest rates after applying the impact of these hedging instruments.

How do we manage foreign exchange risk?

Management policy

Foreign currency hedging activities protect the group from the risk that changes in exchange rates will adversely affect future net cash flows.

The BT Group plc Board’s policy for foreign exchange risk management defines the types of transactions typically covered, including significant operational, funding and currency interest exposures, and the period over which cover should extend for each type of transaction.

The BT Group plc Board has delegated short-term foreign exchange management to the treasury operation and long-term foreign exchange management decisions require further approval from the BT Group plc group chief financial officer, group director tax, treasury and insurance or the group treasurer.

Hedging strategy

A significant proportion of our external revenue and costs arise within the UK and are denominated in Sterling. Our non-UK operations generally trade and are funded in their functional currency which limits their exposure to foreign exchange volatility.

We enter into forward currency contracts to hedge foreign currency capital purchases, purchase and sale commitments, interest expense and foreign currency investments. The commitments hedged are principally denominated in US Dollar, Euro and Asia Pacific region currencies. As a result, our exposure to foreign currency arises mainly on non-UK subsidiary investments and on residual currency trading flows.

We use cross-currency swaps to swap foreign currency borrowings into Sterling.

The table below reflects the currency and interest rate profile of our loans and borrowings after the impact of hedging.

	2018						2017						2016
At 31 March	Fixed rate interest £m		Floating rate interest £m		Total £m		Fixed rate interest £m		Floating rate interest £m		Total £m		Fixed rate interest £m		Floating rate interest £m		Total £m
Sterling		11,990		1,720		13,710		9,633		1,864		11,497		11,417		2,752		14,169
Euro	–			509		509	–			641		641	–			587		587
Total		11,990		2,229		14,219		9,633		2,505		12,138		11,417		3,339		14,756
Ratio of fixed to floating		84%		16%	100%			79%		21%	100%			77%		23%	100%
Weighted average effective
fixed interest rate – Sterling	4.4%						4.9%						6.0%

The floating rate loans and borrowings bear interest rates fixed in advance for periods ranging from one day to one year, primarily by reference to LIBOR quoted rates.

Sensitivity analysis

The income statement and shareholder’s equity are exposed to volatility arising from changes in interest rates and foreign exchange rates. To demonstrate this volatility, management have concluded that the following are reasonable benchmarks for performing sensitivity analysis:

–  For interest, a 1% increase in interest rates and parallel shift in yield curves across Sterling, US Dollar and Euro currencies.

–  For foreign exchange, a 10% strengthening/weakening in Sterling against other currencies.

The impact on equity, before tax, of a 1% increase in interest rates and a 10% strengthening in Sterling against other currencies is as detailed below:

At 31 March	2018 £m Increase (reduce)			2017 £m Increase (reduce)			2016 £m Increase (reduce)
Sterling interest rates		628			554			626
US Dollar interest rates		(267	)		(348	)		(374	)
Euro interest rates		(401	)		(229	)		(263	)
Sterling strengthening		(236	)		(269	)		(98	)

A 1% decrease in interest rates and 10% weakening in Sterling against other currencies would have broadly the same impact in the opposite direction.

The impact on the group’s annual net finance expense of a 1% change in interest rates would have been a decrease of £143m (2016/17: £108m, 2015/16: £123m). Our exposure to foreign exchange volatility in the income statement, after hedging, (excluding translation exposures) would not have been material in 2017/18, 2016/17 and 2015/16.

Credit ratings

BT Group plc continues to target a BBB+/Baa1 credit rating over the cycle. We regularly review the liquidity of the group and our funding strategy takes account of medium-term requirements. These include the pension deficit and shareholder distributions.

Our December 2030 bond contains covenants which require us to pay higher rates of interest since our credit ratings fell below A3 in the case of Moody’s or A– in the case of Standard & Poor’s (S&P). Additional interest of 0.25% per year accrues for each ratings category downgrade by each agency below those levels effective from the next coupon date following a downgrade. Based on the total notional value of debt outstanding of £1.9bn at 31 March 2018, our finance expense would increase/decrease by approximately £10m a year if the group’s credit rating were to be downgraded/upgraded, respectively, by one credit rating category by both agencies.

Our credit ratings were as detailed below:

	2018		2017		2016
At 31 March	Rating	Outlook	Rating	Outlook	Rating	Outlook
Rating agency
Moody’s	Baa2	Stable	Baa1	Negative	Baa2	Positive
Standard & Poor’s	BBB+	Negative	BBB+	Negative	BBB	Positive

How do we manage liquidity risk?

Management policy

We maintain liquidity by entering into short and long-term financial instruments to support operational and other funding requirements, determined using short and long-term cash forecasts. These forecasts are supplemented by a financial headroom analysis which is used to assess funding adequacy for at least a 12-month period. On at least an annual basis the BT Group plc Board reviews and approves the long-term funding requirements of the group and on an ongoing basis considers any related matters. We manage refinancing risk by limiting the amount of borrowing that matures within any specified period and having appropriate strategies in place to manage refinancing needs as they arise. The maturity profile of our loans and borrowings at 31 March 2018 is disclosed in note 23. We have term debt maturities of £1.6bn in 2018/19.

Our treasury operation reviews and manages our short-term requirements within the parameters of the policies set by the BT Group plc Board. We hold cash, cash equivalents and current investments in order to manage short-term liquidity requirements. At 31 March 2018 we had undrawn committed borrowing facilities of £2.1bn (2016/17: £2.1bn, 2015/16: £1.5bn) maturing in September 2021.

The group has no material debt factoring arrangements in place.  In the UK, the group has arranged for a funder to offer a supplier financing scheme to the group’s suppliers. This enables suppliers who sign up to the arrangement to sell their invoices to the funder and to be paid earlier than the invoice due date. The group assesses the arrangement against indicators to assess if debts which vendors have sold to the funder under the supplier financing scheme continue to meet the requirement to be disclosed as trade payables or should be classified as borrowings. At 31 March 2018 the payables met the criteria of trade payables.

Maturity analysis

The following table provides an analysis of the remaining contractually-agreed cash flows including interest payable for our non- derivative financial liabilities on an undiscounted basis, which therefore differs from both the carrying value and fair value.

Non-derivative financial liabilities At 31 March 2018	Loans and other borrowings £m		Interest on loans and other borrowings £m			Trade and other payables £m		Provisions £m			Total £m
Due within one year		2,120		468			4,961		54			7,603
Between one and two years		1,192		421		–			34			1,647
Between two and three years		1,332		381		–			25			1,738
Between three and four years		18		374		–			43			435
Between four and five years		1,489		372		–			19			1,880
After five years		8,943		3,300		–			197			12,440
		15,094		5,316			4,961		372			25,743
Interest payments not yet accrued	–			(5,147	)	–		–				(5,147	)
Fair value adjustment		73	–			–		–				73
Impact of discounting	–		–			–			(72	)		(72	)
Carrying value on the balance sheeta		15,167		169			4,961		300			20,597

^a Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Non-derivative financial liabilities At 31 March 2017	Loans and other borrowings £m		Interest on loans and other borrowings £m			Trade and other payables £m		Provisions £m			Total £m
Due within one year		2,602		532			5,298		62			8,494
Between one and two years		1,614		415			–		41			2,070
Between two and three years		1,166		364			–		21			1,551
Between three and four years		1,295		327			–		18			1,640
Between four and five years		12		319			–		17			348
After five years		6,868		2,726			–		310			9,904
		13,557		4,683			5,298		469			24,007
Interest payments not yet accrued		–		(4,494	)		–		–			(4,494	)
Fair value adjustment		150		–			–		–			150
Impact of discounting		–		–			–		(177	)		(177	)
Carrying value on the balance sheeta		13,707		189			5,298		292			19,486

^a Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Non-derivative financial liabilities At 31 March 2016	Loans and other borrowings £m		Interest on loans and other borrowings £m			Trade and other payables £m		Provisions £m			Total £m
Due within one year		3,558		513			5,346		50			9,467
Between one and two years		1,632		435			–		30			2,097
Between two and three years		1,488		357			–		25			1,870
Between three and four years		1,103		343			–		15			1,461
Between four and five years		1,199		308			–		16			1,523
After five years		6,428		2,885			–		326			9,639
		15,408		4,841			5,346		462			26,057
Interest payments not yet accrued		–		(4,643	)		–		–			(4,643	)
Fair value adjustment		179		–			–		–			179
Impact of discounting		–		–			–		(166	)		(166	)
Carrying value on the balance sheeta		15,587		198			5,346		296			21,427

^a Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Trade and other payables are held at amortised cost. The carrying amount of these balances approximates to fair value due to the short maturity of amounts payable.

The following table provides an analysis of the contractually agreed cash flows in respect of the group’s derivative financial instruments. Cash flows are presented on a net or gross basis in accordance with the settlement arrangements of the instruments.

	Derivatives – Analysed by earliest payment datea									Derivatives – Analysed based on holding instrument to maturity
Derivative financial liabilities At 31 March 2018	Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m		Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m
Due within one year		140		587		(547	)		180		91		587		(547	)		131
Between one and two years		135		183		(166	)		152		91		183		(166	)		108
Between two and three years		156		442		(446	)		152		85		69		(47	)		107
Between three and four years		143		52		(29	)		166		80		68		(47	)		101
Between four and five years		161		52		(29	)		184		80		68		(47	)		101
After five years		291		2,234		(2,149	)		376		599		2,575		(2,512	)		662
Totalb		1,026		3,550		(3,366	)		1,210		1,026		3,550		(3,366	)		1,210

^b Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

	Derivatives – Analysed by earliest payment datea									Derivatives – Analysed based on holding instrument to maturity
Derivative financial liabilities At 31 March 2017	Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m		Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m
Due within one year		291		582		(576	)		297		92		582		(576	)		98
Between one and two years		296		1,139		(1,097	)		338		92		1,139		(1,097	)		134
Between two and three years		198		–		–			198		92		–		–			92
Between three and four years		114		–		–			114		88		–		–			88
Between four and five years		104		–		–			104		83		–		–			83
After five years		123		–		–			123		679		–		–			679
Totalb		1,126		1,721		(1,673	)		1,174		1,126		1,721		(1,673	)		1,174

	Derivatives – Analysed by earliest payment datea										Derivatives – Analysed based on holding instrument to maturity
Derivative financial liabilities At 31 March 2016	Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m			Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m
Due within one year		268		263		(250	)		281			91		263		(250	)		104
Between one and two years		386		38		(27	)		397			88		38		(27	)		99
Between two and three years		371		38		(27	)		382			88		38		(27	)		99
Between three and four years		60		838		(836	)		62			90		838		(836	)		92
Between four and five years		81		17		(18	)		80			84		17		(18	)		83
After five years		–		165		(180	)		(15	)		725		165		(180	)		710
Totalb		1,166		1,359		(1,338	)		1,187			1,166		1,359		(1,338	)		1,187

^aCertain derivative financial instruments contain break clauses whereby either the group or bank counterparty can terminate the swap on certain dates and the mark to market position is settled in cash.

^b Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

How do we manage credit risk?

Management policy

Our exposure to credit risk arises from financial assets transacted by the treasury operation (primarily derivatives, investments, cash and cash equivalents) and from trading-related receivables.

For treasury-related balances, the BT Group plc Board’s defined policy restricts exposure to any one counterparty by setting credit limits based on the credit quality as defined by Moody’s and S&P. The minimum credit ratings permitted with counterparties in respect of new transactions are A3/A– for long-term and P1/A1 for short-term investments. If counterparties in respect of existing transactions fall below the permitted criteria we will take action where appropriate.

The treasury operation continuously reviews the limits applied to counterparties and will adjust the limit according to the nature and credit standing of the counterparty, and in response to market conditions, up to the maximum allowable limit set by the BT Group plc Board.

Operational management policy

Our credit policy for trading-related financial assets is applied and managed by each of the customer-facing units to ensure compliance. The policy requires that the creditworthiness and financial strength of customers are assessed at inception and on an ongoing basis. Payment terms are set in accordance with industry standards. Where appropriate, we may minimise risks by requesting securities such as deposits, guarantees and letters of credit. We take proactive steps including constantly reviewing credit ratings of counterparties to minimise the impact of adverse market conditions on trading-related financial assets.

Exposures

The maximum credit risk exposure of the group’s financial assets at the balance sheet date is as follows:

At 31 March	Notes		2018 £m		2017 £m		2016 £m
Derivative financial assets				1,509		2,246		1,639
Investments		21		16,578		13,346		15,236
Trade and other receivablesc		16		2,533		2,754		2,884
Cash and cash equivalents		22		521		526		989
				21,141		18,872		20,748

^cThe carrying amount excludes £317m (2016/17: £360m, 2015/16: £218m) of non-current trade and other receivables which relate to non-financial assets, and £1,496m (2016/17: £1,106m, 2015/16: £1,103m) of prepayments and other receivables.

The credit quality and credit concentration of cash equivalents, current asset investments and derivative financial assets are detailed in the tables below. Where the opinion of Moody’s and S&P differ, the lower rating is used.

Moody’s/S&P credit rating of counterparty	2018 £m		2017 £m		2016 £m
Aa2/AA and above		2,575		1,444		2,878
Aa3/AA–		313		208		120
A1/A+a		651		952		64
A2/Aa		628		370		939
A3/A–a		180		204		160
Baa1/BBB+a		59		561		492
Baa2/BBB and belowa		207		86		–
		4,613		3,825		4,653

^aWe hold cash collateral of £492m (2016/17: £702m, 2015/16: £553m) in respect of derivative financial assets with certain counterparties.

The concentration of credit risk for our trading balances is provided in note 16, which analyses outstanding balances by customer-facing unit. Where multiple transactions are undertaken with a single financial counterparty or group of related counterparties, we enter into netting arrangements to reduce our exposure to credit risk by making use of standard International Swaps and Derivatives Association (ISDA) documentation. We have also entered into credit support agreements with certain swap counterparties whereby, on a daily, weekly and monthly basis, the fair value position on notional £3,162m of long dated cross-currency swaps and interest rate swaps is collateralised. The related net cash outflow during the year was £220m (2016/17: inflow £100m, 2015/16: inflow £79m). The collateral paid and received is recognised within current asset investments and loans and other borrowings, respectively.

Offsetting of financial instruments

The table below shows our financial assets and liabilities that are subject to offset in the group’s balance sheet and the impact of enforceable master netting or similar agreements.

				Related amounts not set off in the balance sheet
Financial assets and liabilities At 31 March 2018	Amounts presented in the balance sheet £m			Right of set off with derivative counterparties £m			Cash collateral £m			Net amount £m
Derivative financial assets		1,509			(754	)		(492	)		263
Derivative financial liabilities		(837	)		754			60			(23	)
Total		672			–			(432	)		240

				Related amounts not set off in the balance sheet
Financial assets and liabilities At 31 March 2017	Amounts presented in the balance sheet £m			Right of set off with derivative counterparties £m			Cash collateral £m			Net amount £m
Derivative financial assets		2,246			(693	)		(702	)		851
Derivative financial liabilities		(903	)		693			64			(146	)
Total		1,343			–			(638	)		705

				Related amounts not set off in the balance sheet
Financial assets and liabilities At 31 March 2016	Amounts presented in the balance sheet £m			Right of set off with derivative counterparties £m			Cash collateral £m			Net amount £m
Derivative financial assets		1,639			(456	)		(553	)		630
Derivative financial liabilities		(911	)		456			40			(415	)
Total		728			–			(513	)		215

Derivatives

All of our derivative financial instruments are held at fair value on the balance sheet. The fair values of outstanding swaps and foreign exchange contracts are estimated using discounted cash flow models and market rates of interest and foreign exchange at the balance sheet date.

At 31 March 2018	Current asset £m		Non-current asset £m		Current liability £m		Non-current liability £m
Designated in a cash flow hedge		187		1,061		41		587
Other		10		251		9		200
Total derivatives		197		1,312		50		787

At 31 March 2017	Current asset £m		Non-current asset £m		Current liability £m		Non-current liability £m
Designated in a cash flow hedge		417		1,508		25		616
Other		11		310		9		253
Total derivatives		428		1,818		34		869

At 31 March 2016	Current asset £m		Non-current asset £m		Current liability £m		Non-current liability £m
Designated in a cash flow hedge		166		1,158		40		618
Other		11		304		8		245
Total derivatives		177		1,462		48		863

All derivative financial instruments are categorised at Level 2 of the fair value hierarchy as defined in note 21, with the exception of a derivative energy contract which is classified at Level 3. The energy derivative was renegotiated during 2016/17 and has been designated as a cash flow hedge. On initial recognition of this contract a loss of £8m was deferred. The fair value of the energy derivative at 31 March 2018 was a liability of £1m (2016/17: liability of £8m, 2015/16: £nil ). It has been valued using assumptions on volumes, inflation and energy prices.

Hedging activities

Derivatives may qualify as hedges for accounting purposes if they meet the criteria for designation as fair value hedges or cash flow hedges in accordance with IAS 39.

Cash flow hedges

Instruments designated in a cash flow hedge include interest rate swaps and cross-currency swaps hedging Euro- and US Dollar- denominated borrowings. Forward currency contracts are taken out to hedge step-up interest on currency denominated borrowings relating to the group’s 2030 US Dollar bond. The hedged cash flows will affect the group’s income statement as interest and principal amounts are repaid over the remaining term of the borrowings (see note 23).

We hedge forecast foreign currency purchases, principally denominated in US Dollar, Euro and Asia Pacific currencies 12 months forward with certain specific transactions hedged further forward. The related cash flows are recognised in the income statement over this period.

All cash flow hedges were effective in the period. See note 26 for details of the movements in the cash flow reserve.

Other derivatives

Our policy is not to use derivatives for speculative purposes. However, due to the complex nature of hedge accounting under IAS 39, some derivatives may not qualify for hedge accounting, or are specifically not designated as a hedge where natural offset is more appropriate. Derivative instruments that do not qualify for hedge accounting are classified as held for trading and held at fair value through profit or loss under IAS 39.

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Other reserves

12 Months Ended

Mar. 31, 2018

Disclosure Of Other Reserves [Abstract]

Other reserves

26. Other reserves

	Other comprehensive income
	Cash flow reserve £m		a	Available- for-sale reserve £m		b	Translation reserve £m		c	Merger and other reserves £m		d	Total £m
At 1 April 2015		55			18			278			858			1,209
Exchange differences		–			–			29			–			29
Net fair value gain on cash flow hedges		381			–			–			–			381
Recognised in income and expense		(230	)		–			–			–			(230	)
Fair value movement on available-for-sale assets		–			(2	)		–			–			(2	)
Tax recognised in other comprehensive income		(33	)		–			38			–			5
At 1 April 2016		173			16			345			858			1,392
Exchange differences		–			–			227			–			227
Net fair value gain on cash flow hedges		884			–			–			–			884
Recognised in income and expense		(938	)		–			–			–			(938	)
Fair value movement on available-for-sale assets		–			(3	)		–			–			(3	)
Tax recognised in other comprehensive income		8			–			21			–			29
At 31 March 2017		127			13			593			858			1,591
Exchange differencese		–			–			(188	)		–			(188	)
Net fair value loss on cash flow hedges		(368	)		–			–			–			(368	)
Recognised in income and expense		277			–			–			–			277
Fair value movement on available-for-sale assets		–			11			–			–			11
Tax recognised in other comprehensive income		10			–			(9	)		–			1
Transfer to realised profit		(83	)		–			–			–			(83	)
At 31 March 2018		(37	)		24			396			858			1,241

^a The cash flow reserve is used to record the effective portion of the cumulative net change in the fair value of cash flow hedging instruments related to hedged transactions that have not yet occurred. Amounts ‘recognised in income and expense’ include a net credit to the cash flow reserve of £295m (2016/17: charge of £941m, 2015/16: charge of £255m) relating to fair value movements on derivatives. The items generating these foreign exchange movements are in designated cash flow hedge relationships.

^b The available-for-sale reserve is used to record the cumulative fair value gains and losses on available-for-sale financial assets. The cumulative gains and losses are recycled to the income statement on disposal of the assets.

^c The translation reserve is used to record cumulative translation differences on the assets and liabilities of foreign operations. The cumulative translation differences are recycled to the income statement on disposal of the foreign operation.

^d Excludes £1m (2016/17: £10m, 2015/16: £nil) of exchange differences in relation to retained earnings attributed to non-controlling interests.

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Directors emoluments and pensions

12 Months Ended

Mar. 31, 2018

Disclosure Of Defined Benefit Plans [Abstract]

Directors emoluments and pensions

27. Directors’ emoluments and pensions

The directors at 31 March 2018 were Glyn Parry who served throughout 2017/18 and Patrick Bradley, Neil Harris and Simon Lowth who were appointed on 17 October 2017. Sean Williams served as a director until 29 September 2017 and Linda Bruce-Watt served as a director from 29 September 2017 until 17 October 2017.

For the year ended 31 March 2018 the aggregate emoluments of the directors excluding deferred bonuses of £319,000 (2016/17: £88,000) was £2,525,000 (2016/17: £1,149,000). Deferred bonuses are payable in 5p ordinary shares of BT Group plc in three years’ time subject to continuous employment.

Retirement benefits were accruing to no directors (2016/17: one) under a money purchase scheme.

During the year no director exercised options (2016/17: none) under BT Group share option plans. Six directors who held office for the whole or part of the year (2016/17: three) received or are entitled to receive 5p ordinary shares of BT Group plc under BT long-term incentive plans. The aggregate value of BT Group plc shares which vested to directors during the year under BT long-term incentive plans was £179,000 (2016/17: £2,646,000).

The emoluments of the highest paid director excluding his deferred bonus of £302,400 (2016/17: £36,000) were £1,538,000 (2016/17: £492,000). He is entitled to receive 1,612,997 BT Group plc 5p ordinary shares under BT long-term incentive plans subject to continuous employment and in some cases to certain performance conditions being met.

Included in the above aggregate emoluments are those of Simon Lowth who is also a director of the ultimate holding company, BT Group plc.  The directors do not believe it is practicable for the purposes of this report to apportion the amount of total emoluments received by him between his services as director of the company and his services as director of BT Group plc.

The emoluments of the directors are calculated in accordance with the statutory provisions applicable to the company.

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Related Party Transactions

12 Months Ended

Mar. 31, 2018

Disclosure Of Transactions Between Related Parties [Abstract]

Related Party Transactions

28.Related party transactions

Key management personnel comprise executive and non-executive directors and members of the BT Group plc Executive Committee as well as the directors of the company. Compensation of key management personnel is disclosed in note 5.

Amounts paid to the group’s retirement benefit plans are set out in note 19.

British Telecommunications plc and certain of its subsidiaries act as a funder and deposit taker for cash related transactions for both its parent and ultimate parent company. The loan arrangements described below with these companies reflect this. Cash transactions usually arise where the parent and ultimate parent company are required to meet their external payment obligations or receive amounts from third parties. These principally relate to the payment of dividends, the buyback of shares, the exercise of share options and the issuance of ordinary shares. Transactions between the ultimate parent company, parent company and the group are settled on both a cash and non-cash basis through these loan accounts depending on the nature of the transaction.

In 2001/02 the group demerged its former mobile phone business and as a result BT Group plc became the listed ultimate parent company of the remaining group. The demerger steps resulted in the formation of an intermediary holding company, BT Group Investments Limited, between BT Group plc and British Telecommunications plc. This intermediary company held an investment of £18.5bn in British Telecommunications plc which was funded by an intercompany loan facility with British Telecommunications plc.

No dividend was declared in relation to the year ended 31 March 2017 and therefore there was no settlement in the year ended 31 March 2018 (31 March 2017: £2,350m). A dividend of £2,500m has been declared in relation to the year ended 31 March 2018. This was declared after 31 March 2018 so no liability (amount owed to parent company) is recorded in these financial statements. See note 10 and the group statement of changes in equity.

The loan facilities with both the parent company and ultimate parent company accrue interest at a rate of LIBOR plus 102.5 basis points, and are subject to an overall maximum of £25bn and £10bn respectively. The parent company currently finances its obligations on the loan as they fall due through dividends paid by the company.

In 2015/16 the ultimate parent company of the group raised £1.0bn from an equity placing and entered into an additional intercompany loan agreement with British Telecommunications plc for this amount. This amount was raised to support BT Group plc’s planned acquisition of EE.

A summary of the balances with the parent and ultimate parent companies and the finance income or expense arising in respect of these balances is set out below:

			2018						2017						2016
	Notes		Asset (liability) at 31 March £m			Finance income (expense) £m			Asset (liability) at 31 March £m			Finance income (expense) £m			Asset (liability) at 31 March £m			Finance income (expense) £m
Amounts owed by (to) parent company
Loan facility – non-current assets investments	21,24			10,318			169			10,191			191			10,510			326
Loan facility  – current asset investments		21		168		n/a				192		n/a				327		n/a
Trade and other payables		17		(50	)	n/a				(63	)	n/a				(70	)	n/a
Amounts owed by (to) ultimate parent companya
Non-current assets investments	21,24			2,983			34			1,371			28			1,409			26
Non-current liabilities loans		23		(1,044	)		(18	)		(1,024	)		(25	)		(1,004	)		(20	)
Trade and other receivables		16		15		n/a				25		n/a				9		n/a
Current asset investments		21		34		n/a				28		n/a				26		n/a
Current liabilities loans		23		(18	)	–				(159	)	–				(20	)	–

^aDuring the year we made cash payments of £1,722m to BT Group plc offset by the receipt of £45m from BT Group plc resulting in net cash outflow of £1,677m. In addition there are non cash movements of £63m on non-current asset investments relating to interest on loans, employee share schemes and tax settlements made by BT plc on behalf of BT Group plc.

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Financial commitments and contingent liabilities

12 Months Ended

Mar. 31, 2018

Financial Commitments [Abstract]

Financial commitments and contingent liabilities

29. Financial commitments and contingent liabilities

Financial commitments were as follows:

At 31 March	2018 £m		2017 £m
Capital commitments		993		889
Other commitments		362		367
Device purchase commitments		262		423
TV programme rights commitments		2,823		2,644
Total		4,440		4,323

TV programme rights commitments, mainly relating to football broadcast rights, are those for which the licence period has not yet started.

Future minimum operating lease payments were as follows:

	2018 £m		2017 £m
Payable in the year ending 31 March:
2018		–		650
2019		600		610
2020		550		558
2021		513		532
2022		486		505
2023		463		475
Thereafter		3,985		3,830
Total future minimum operating lease payments		6,597		7,160

Operatinglease commitmentswere mainly in respectoflandand buildingswhich arose from a sale and operating leasebacktransaction in 2001. Leases have an averageterm of14 years(2016/17:15 years) and rentals are fixed for an average of14 years(2016/17:15 years).

Otherthan as disclosed below,there were no contingent liabilities or guaranteesat31 March 2018 other thanthose arising inthe ordinary course of the group’s business and on these no material losses are anticipated. We have insurance cover to certain limits for major risks on property and major claims in connection with legal liabilities arising in the course of our operations. Otherwise, the group generally carries its own risks.

Commitments and guarantees

BDUK

Under the Broadband Delivery UK programme, grants received by the group may be subject to reinvestment or repayment to the customer depending on the level of take-up.

TelefónicaUKLimitedleases

We’ve provided guaranteesrelating tocertainleases entered intoby TelefónicaUK Limited(formerlyO2UK Limited)prior to the demerger of mmO2fromBTon 19 November2001.mmO2 plc(now partof the TelefónicaGroup) has givenBTa counter indemnityfor these guarantees.Thereis no exposure in theevent of credit defaultin respect ofamounts used to defease futurelease obligations.The guaranteelasts until TelefónicaUKLimited hasdischarged all its obligations.

Legalproceedings

The group is involved in various legal proceedings, including actual or threatened litigation, government or regulatory investigations. However, save as disclosed below, the group does not currently believe that there are any legal proceedings, or government or regulatory investigations that may have a material adverse impact on the operations or financial condition of the group. In respect of each of the claims below, the nature and progression of such proceedings and investigations can make it difficult to predict the impact they will have on the group. There are many reasons why we cannot make these assessments with certainty, including, among others, that they are in early stages, no damages or remedies have been specified, and/or the often slow pace of litigation.

Italianbusiness

In the prior year, our parent company, BT Group plc, made an announcement with respect to the investigation into our Italian business. The issues in Italy have also resulted in engagement with certain of our regulators and other authorities. We are cooperating fully with these bodies.

Following this announcement, three purported securities class action complaints were filed against BT Group plc and certain current and former officers in United States courts. The two actions brought in New York have since been voluntarily dismissed by the plaintiffs in those actions. On 21 November 2017, the lead plaintiff in the District of New Jersey action filed an amended complaint brought on behalf of purchasers of BT Group ADRs between May 2013 and January 2017, regarding allegations that BT Group plc made materially false and/or misleading statements during the class period. On 22 January 2018 BT Group plc filed a motion to dismiss the amended complaint and the plaintiffs filed their reply to that motion on 23 March 2018. BT Group plc filed a response to their reply on 7 May 2018 and expect the court to schedule oral argument on the motion.

Phones 4U

In December 2016, the administrators of Phones 4U Limited (P4U) started legal proceedings in the High Court in the United Kingdom against EE, claiming payments under a retail trading agreement for sums then due in respect of revenues (net of costs) from certain customers prior to P4U entering administration. This sharing of revenue under the retail trading agreement was due to continue until September 2019, with related payments continuing until April 2021. On 8 May 2018 we reached a confidential agreement with the administrators of P4U to settle this matter. This settlement is in line with the accruals we held to cover potential payments required by EE.

Since 2015 the administrators have separately made allegations that EE and other mobile network operators colluded to procure P4U’s insolvency. We dispute these allegation vigorously and to date no proceedings have been issued.

Hutchinson 3G Limited

In May 2016, Hutchinson 3G Limited (H3G) brought legal proceedings in the High Court in the United Kingdom against EE, alleging breach of contract relating to alleged delays in the roll out of certain free carrier coverage to H3G. H3G is entitled to this free carrier coverage under arrangements agreed following the merger of Orange and T-Mobile, predecessors of EE. H3G claimed damages relating to loss of business of £167m. During the year the parties have resolved this matter to their mutual satisfaction and have discontinued the High Court proceedings.

Brazilian tax claims

The Brazilian state tax authorities have made tax demands against certain Brazilian subsidiaries relating to the Tax on Distribution of Goods and Services (ICMS), an indirect tax imposed on the provision of telecommunications services in Brazil. The state tax authorities are seeking to impose ICMS on revenues earned on activities that the company does not consider as being part of the provision of telecommunications services, such as equipment rental and managed services. We have disputed the basis on which ICMS is imposed and the rate which the tax authorities are seeking to apply. We currently have 32 ICMS cases with a current potential value of £219m all covering assessments made for the period up to 2012, except for one case valued at £1.2m that covers the period 2013 to 2016. The judicial process is likely to take many years. There are eight cases, worth approximately £43m, that are pending appeal before the Sao Paulo Court of Appeal. A hearing for these eight cases took place on 21 February 2018 and a further hearing will take place in the coming months.

Regulatory matters

In respect of regulatory risks, the group provides for anticipated costs where an outflow of resources is considered probable and a reasonable estimate can be made of the likely outcome. Estimates are used in assessing the likely value of the regulatory risk. The ultimate liability may vary from the amounts provided and will be dependent upon the eventual outcome of any settlement.

We hold provisions for regulatory risks. These provisions cover the following issues:

Deemed Consent

Deemed Consent is an agreed process between Openreach and its Communications Provider (CP) customers, which allows Openreach to halt the installation and reschedule the delivery date for providing dedicated business services (known as Ethernet) in a number of specific circumstances where it is beyond its control. Ofcom found that Openreach had breached its contractual and regulatory obligations by inadequately and retrospectively applying Deemed Consent to reduce compensation payments to CPs between January 2013 and December 2014.

We continue to estimate the total compensation payments will amount to around £300m. However, the precise amount will result from discussions with affected parties, and could result in lower or higher payments.

Other regulatory matters

The remaining provision reflects management’s estimates of regulatory risks across a range of issues, including price and service issues. The precise outcome of each matter depends on whether it becomes an active issue, and the extent to which negotiation or regulatory decision will result in financial settlement.

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Post Balance Sheet Events

12 Months Ended

Mar. 31, 2018

Disclosure Of Nonadjusting Events After Reporting Period [Abstract]

Post Balance Sheet Events

30. Post balance sheet events

Changes to our segments

From 1 April 2018, our existing BT Consumer and EE divisions have been brought together into a combined division, Consumer, to drive converged products and accelerate transformation. From 1 October 2018, our existing Business and Public Sector and Wholesale and Ventures divisions will be brought together into a combined division, Enterprise, to accelerate transformation, simplify our operating model and strengthen accountabilities.

These businesses operated and were reported separately throughout 2017/18 and therefore have been presented as separate operating segments throughout these accounts.

These organisational changes do not impact the results of Global Services or Openreach and there is no impact on the total group results, balance sheet or cash flows. There are no internal revenue and costs between EE and BT Consumer. In 2017/18, there were £32m (2016/17: £22m, 2015/16: £24m) of internal revenue and costs between Business and Public Sector and Wholesale and Ventures.

We have set out below the segment analysis outlining the impacts of this change that will be applicable to the annual financial statements for 2018/19. Full details of the internal revenue and costs at the disaggregated level are provided in note 4.

Segment revenue and profit

Year ended 31 March 2018	Consumer £m			Enterprise £m			Global Services £m			Openreach £m			Other £m			Total £m
Segment revenue		10,360			6,540			5,013			5,123			8			27,044
Internal revenue		(103	)		(217	)		–			(2,978	)		–			(3,298	)
Revenue from external customersa		10,257			6,323			5,013			2,145			8			23,746
EBITDAb		2,376			2,172			434			2,520			6			7,508
Depreciation and amortisation		(992	)		(676	)		(424	)		(1,360	)		(62	)		(3,514	)
Operating profit (loss)a		1,384			1,496			10			1,160			(56	)		3,994
Specific items																	(610	)
Operating profit																	3,384
Net finance expensec																	(579	)
Share of post tax loss of associates and joint ventures																	(1	)
Profit before tax																	2,804

^aBefore specific items.

^bEBITDA is stated before specific items and is the group’s profitability measure for segments.

^cNet finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

Year ended 31 March 2017	Consumer £m			Enterprise £m			Global Services £m			Openreach £m			Other £m			Total £m
Segment revenue		10,024			6,845			5,479			5,098			10			27,456
Internal revenue		(100	)		(238	)		–			(3,036	)		–			(3,374	)
Revenue from external customersa		9,924			6,607			5,479			2,062			10			24,082
EBITDAb		2,168			2,362			495			2,633			(10	)		7,648
Depreciation and amortisation		(989	)		(658	)		(439	)		(1,369	)		(55	)	(3,510)
Operating profit (loss)a		1,179			1,704			56			1,264			(65	)		4,138
Specific items																(968)
Operating profit																	3,170
Net finance expensec																	(610	)
Share of post tax loss of associates and joint ventures																	(9	)
Profit before tax																	2,551

Year ended 31 March 2016	Consumer £m			Enterprise £m			Global Services £m			Openreach £m			Other £m			Total £m
Segment revenue		5,449			6,544			5,074			5,100			11			22,178
Internal revenue		(72	)		(169	)		–			(3,058	)		–			(3,299	)
Revenue from external customersa		5,377			6,375			5,074			2,042			11			18,879
EBITDAb		1,228			2,169			479			2,659			(77	)		6,458
Depreciation and amortisation		(353	)		(537	)		(422	)		(1,301	)		(18	)		(2,631	)
Operating profit (loss)a		875			1,632			57			1,358			(95	)		3,827
Specific items																	(212	)
Operating profit																	3,615
Net finance expensec																	(380	)
Share of post tax loss of associates and joint ventures																	6
Profit before tax																	3,241

^aBefore specific items.

^bEBITDA is stated before specific items and is the group’s profitability measure for segments.

^cNet finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

Internal revenue and costs

Year ended 31 March 2018	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
Consumer		–		65		20		–		18		103
Enterprise		67		–		42		42		66		217
Global Services		–		–		–		–		–		–
Openreach		896		442		125		–		1,515		2,978
Total		963		507		187		42		1,599		3,298

Year ended 31 March 2017	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
Consumer		–		62		20		–		18		100
Enterprise		63		–		62		39		74		238
Global Services		–		–		–		–		–		–
Openreach		910		496		158		–		1,472		3,036
Total		973		558		240		39		1,564		3,374

Year ended 31 March 2016	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
Consumer		–		31		23		–		18		72
Enterprise		73		–		40		56		–		169
Global Services		–		–		–		–		–		–
Openreach		905		526		173		–		1,454		3,058
Total		978		557		236		56		1,472		3,299

Capital expenditure

Year ended 31 March 2018	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Intangible assets		236		180		92		70		64		642
Property, plant and equipment		683		353		186		1,588		70		2,880
Capital expenditurea		919		533		278		1,658		134		3,522

Year ended 31 March 2017	Consumer £m		BT Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Intangible assets		225		141		126		74		55		621
Property, plant and equipment		628		360		235		1,499		111		2,833
Capital expenditurea		853		501		361		1,573		166		3,454

Year ended 31 March 2016	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Intangible assets		117		106		62		62		65		412
Property, plant and equipment		186		256		293		1,385		90		2,210
Capital expenditurea		303		362		355		1,447		155		2,622

^aNet of government grants.

As at 31 March 2018, Consumer had 18,200 (2016/17: 17,900, 2015/16: 15,700) employees and an average of 18,000 (2016/17: 16,800, 2015/16: 7,600) for the year on a full-time equivalent basis. Enterprise had 13,900 as at 31 March 2018 (2016/17: 14,100, 2015/16: 14,000) and an average of 14,200 for the year ended 31 March 2018 (2016/17: 13,900, 2015/16: 13,100).

Consumer had trade receivables not passed due of £363m (2016/17: £463m, 2015/16: £405m) and accrued income of £208m (2016/17: £260m, 2015/16: £395m) as at 31 March 2018. Enterprise had trade receivables not passed due of £345m (2016/17: £275m, 2015/16: £191m) and accrued income of £279m (2016/17: £318m, 2015/16: £245m).

Contingent liabilities

Since the reporting date, we have reached a confidential settlement with the administrators of P4U regarding its claim for revenue share which relates to certain customers prior to P4U insolvency. This settlement is in line with the accruals we held to cover potential payments required by EE.

Acquisition of spectrum

In April 2018 we secured 40MHz of 3.4GHz spectrum at a cost of £304m allowing us to progress with our 5G plans and strengthening our position as the mobile network leader. The spectrum auction bidding cut across the 2017/18 and 2018/19 financial years. We had £325m on deposit with Ofcom at 31 March 2018, the excess deposit balance of £21m has since been refunded.

Strategy update

In May 2018 we are announcing an update to our strategy to accelerate leadership in converged connectivity and services. Our strategy will drive sustainable growth in value by focusing on delivering differentiated customer experiences, investing in integrated network leadership, and transforming our operating model and includes the repositioning of Global Services as a more focused digital business. This also includes the next phase of our restructuring programme. This programme involves the reduction of c13,000 mainly back office and middle management roles at a cost of £800m with a two–year payback and expected year three cash cost reduction of £1.5bn. The balances of the first phase of our restructuring programme (£60m of cost and removal of 1,200 FTE roles) and our EE integration programme (further run rate synergies of £110m) are included in the this wider transformation programme.

Triennial valuation of BT Pension Scheme

In May 2018 we concluded the 30 June 2017 triennial valuation of the BT Pension Scheme. Details are set out in note 19.

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Significant accounting policies (Policies)

12 Months Ended

Mar. 31, 2018

Significant Accounting Policies [Abstract]

Basis of consolidation

Basis of consolidation

The group financial statements consolidate the financial statements of British Telecommunications plc and its subsidiaries, and include its share of the results of associates and joint ventures using the equity method of accounting. The group recognises its direct rights to (and its share of) jointly held assets, liabilities, revenues and expenses of joint operations under the appropriate headings in the consolidated financial statements.

A subsidiary is an entity that is controlled by another entity, known as the parent or investor. An investor controls an investee when the investor is exposed, or has rights, to variable returns from its involvement with the investee and has the ability to affect those returns through its power over the investee.

Non-controlling interests in the net assets of consolidated subsidiaries, which consist of the amounts of those interests at the date of the original business combination and non-controlling share of changes in equity since the date of the combination, are not material to the group’s financial statements.

The results of subsidiaries acquired or disposed of during the year are consolidated from and up to the date of change of control. Where necessary, accounting policies of subsidiaries have been aligned with the policies adopted by the group. All intra-group transactions including any gains or losses, balances, income or expenses are eliminated in full on consolidation.

When the group loses control of a subsidiary, the profit or loss on disposal is calculated as the difference between (i) the aggregate of the fair value of the consideration received and the fair value of any retained interest and (ii) the previous carrying amount of the assets (including goodwill), and liabilities of the subsidiary and any non-controlling  interests. The profit or loss on disposal is recognised as a specific item.

Revenue

Revenue

Revenue represents the fair value of the consideration received or receivable for communications services and equipment sales, net of discounts and sales taxes. Revenue is recognised when it is probable that the economic benefits associated with a transaction will flow to the group and the amount of revenue and associated costs can be measured reliably. The accounting for revenue sharing arrangements depends on the analysis of the facts and circumstances surrounding these transactions.

Where we act as an agent in a transaction, we recognise revenue net of directly attributable costs.

Services

Revenue arising from separable installation and connection services is recognised when it is earned, upon activation. Revenue from the rental of analogue and digital lines and private circuits as well as wholesale access revenue is recognised on a straight line basis over the period to which it relates. Revenue from calls is recognised at the time the call is made over our network. Subscription fees, consisting primarily of monthly charges for access to broadband and other internet access or voice services, are recognised as revenue as the service is provided. Revenue from the interconnection of voice and data traffic between other telecommunications operators is recognised at the time of transit across our network.

Equipment sales

Revenue from the sale of equipment is recognised when all the significant risks and rewards of ownership are transferred to the customer, which is normally the date the equipment is delivered and accepted by the customer.

Long-term contractual arrangements

Revenue from long-term contractual arrangements, including fixed price contracts to design and build software solutions, is recognised based on the percentage of completion method. The stage of completion is estimated using an appropriate measure according to the nature of the contract such as the proportion of costs incurred relative to the estimated total contract costs, or other measures of completion such as the achievement of contract milestones and customer acceptance. In the case of time and materials contracts, revenue is recognised as the service is rendered.

Costs related to delivering services under long-term contractual arrangements are expensed as incurred except for an element of costs incurred in the initial contract set-up, transition or transformation phase, which is deferred and recorded within non-current assets. These costs are then recognised in the income statement on a straight line basis over the remaining contract term, unless the pattern of service delivery indicates a different profile is more appropriate. These costs are directly attributable to specific contracts, relate to future activity, will generate future economic benefits and are assessed for recoverability on a regular basis.

The percentage of completion method relies on estimates of total expected contract revenues and costs, as well as reliable measurement of the progress made towards completion. Unless the financial outcome of a contract can be estimated with reasonable certainty, no attributable profit is recognised. In such circumstances, revenue is recognised equal to the costs incurred to date, to the extent that such revenue is expected to be recoverable, or costs are accrued to bring the margin to nil. Recognised revenue and profits are subject to revisions during the contract if the assumptions regarding the overall contract outcome are changed. The cumulative impact of a revision in estimates is recorded in the period in which such revisions become likely and can be estimated. Where the actual and estimated costs to completion exceed the estimated revenue for a contract, the full contract life loss is recognised immediately.

Multiple element arrangements and bundles

Revenue from multiple element arrangements and bundles is described in note 4.

Operating and reportable segments

Operating and reportable segments

Our operating segments are reported based on financial information provided to the Executive Committee of BT Group plc which is the key management committee and represents the ‘chief operating decision maker’.

Our organisational structure reflects the different customer groups to which we provide communications products and services via our customer-facing units: BT Consumer, EE, Business and Public Sector, Global Services, Wholesale and Ventures and Openreach. The customer-facing units are supported by an internal service unit: Technology, Service & Operations (TSO).

The customer-facing units are our reportable segments and generate substantially all of our revenue. We aggregate the remaining operations and include within the ‘Other’ category to reconcile to the consolidated results of the group. The ‘Other’ category includes TSO and our corporate units including procurement and property management.

Provisions for the settlement of significant legal, commercial and regulatory disputes, which are negotiated at a group level, are initially recorded in the ‘Other’ segment. On resolution of the dispute, the full impact is recognised in the results of the relevant customer-facing unit and offset in the group results through the utilisation of the provision previously charged to the ‘Other’ segment. Settlements which are particularly significant or cover more than one financial year may fall within the definition of specific items as detailed on page 209.

The costs incurred by TSO are recharged to the customer-facing units to reflect the services it provides to them. Depreciation and amortisation incurred by TSO in relation to the networks and systems it manages and operates on behalf of the customer-facing units is allocated to the customer-facing units based on their respective utilisation. Capital expenditure incurred by TSO for specific projects undertaken on behalf of the customer-facing units is allocated based on the value of the directly attributable expenditure incurred. Where projects are not directly attributable to a particular customer-facing unit, capital expenditure is allocated between them based on the proportion of estimated future economic benefits. TSO and the group’s corporate functions are not reportable segments as they did not meet the quantitative thresholds as set out in IFRS 8 ‘Operating Segments’ for any of the years presented.

Performance of each reportable segment is measured based on adjusted EBITDA, defined as EBITDA before specific items, as included in the internal financial reports reviewed by the Executive Committee of BT Group plc. EBITDA is defined as the operating profit or loss before depreciation, amortisation, net finance expense and taxation. Adjusted EBITDA is considered to be a useful measure of the operating performance of the customer-facing units because it approximates the underlying operating cash flow by eliminating depreciation and amortisation and also provides a meaningful analysis of trading performance by excluding specific items, which are disclosed separately by virtue of their size, nature or incidence. Specific items are detailed in note 8 and are not allocated to the reportable segments as this reflects how they are reported to the Executive Committee of BT Group plc. Finance expense and income are not allocated to the reportable segments, as the central treasury function manages this activity, together with the overall net debt position of the group.

On 1 April 2018, our BT Consumer and EE customer-facing units were brought together to drive converged products and accelerate transformation. Additionally, Business and Public Sector and Wholesale and Ventures will be brought together from 1 October 2018. Each of these businesses operated separately throughout 2017/18 and therefore have been presented as four separate operating segments throughout these financial statements, unless explicitly stated otherwise. For further information see note 30.

Retirement benefits

Retirement benefits

The group’s net obligation in respect of defined benefit pension plans is the present value of the defined benefit obligation less the fair value of the plan assets.

The calculation of the obligation is performed by a qualified actuary using the projected unit credit method and key actuarial assumptions at the balance sheet date.

The income statement expense is allocated between an operating charge and net finance income or expense. The operating charge reflects the increase in the defined benefit obligation resulting from the pension benefit earned by active employees in the current period, the costs of administering the plans and any past service costs/credits such as those arising from curtailments or settlements. The net finance income or expense reflects the interest on the net retirement benefit obligations recognised in the group balance sheet, based on the discount rate at the start of the year. Actuarial gains and losses are recognised in full in the period in which they occur and are presented in the group statement of comprehensive income.

The group also operates defined contribution pension plans and the income statement expense represents the contributions payable for the year.

Property, plant and equipment

Property, plant and equipment

Property, plant and equipment are included at historical cost, net of accumulated depreciation, government grants and any impairment charges. Property, plant and equipment acquired through business combinations are initially recorded at fair value and subsequently accounted for on the same basis as the group’s existing assets. An item of property, plant and equipment is derecognised on disposal or when no future economic benefits are expected to arise from the continued use of the asset. The difference between the sale proceeds and the net book value at the date of disposal is recognised in operating costs in the income statement.

Included within the cost of network infrastructure and equipment are direct and indirect labour costs, materials and directly attributable overheads.

Depreciation is provided on property, plant and equipment on a straight line basis from the time the asset is available for use, to write off the asset’s cost over the estimated useful life taking into account any expected residual value. Freehold land is not depreciated.

The estimated useful lives assigned to principal categories of assets are as follows:

Land and buildings
–  Freehold buildings	14 to 50 years
–  Short-term leasehold improvements				Shorter of 10 years or lease term
–  Leasehold land and buildings		Unexpired portion of lease or 40 years, whichever is the shorter
Network infrastructure
Transmission equipment
–  Duct		40 years
–  Cable		3 to 25 years
–  Fibre		5 to 20 years
Exchange equipment		2 to 13 years
Other network equipment		2 to 20 years
Other assets
–  Motor vehicles		2 to 9 years
–  Computers and office equipment			3 to 7 years

Assets held under finance leases are depreciated over the shorter of the lease term or their useful economic life. Residual values and useful lives are reassessed annually and, if necessary, changes are recognised prospectively.

Network share assets

Network share assets

Certain assets have been contributed to a network share arrangement by both EE and Hutchison 3G UK Limited, with legal title remaining with the contributor. This is considered to be a reciprocal arrangement. The group’s share of the assets on acquisition of EE was recognised at fair value within tangible assets, and depreciated in line with the group’s policy. Subsequent additions are recorded at cost. For further information see note 12.

Intangible assets

Intangible assets

Identifiable intangible assets are recognised when the group controls the asset, it is probable that future economic benefits attributable to the asset will flow to the group and the cost of the asset can be reliably measured. All intangible assets, other than goodwill, are amortised over their useful economic life. The method of amortisation reflects the pattern in which the assets are expected to be consumed. If the pattern cannot be determined reliably, the straight line method is used.

Goodwill

Goodwill represents the excess of the cost of an acquisition over the fair value of the group’s share of the identifiable net assets (including intangible assets) of the acquired business.

For the purpose of impairment testing, goodwill acquired in a business combination is allocated to each of the Cash Generating Units (CGUs) that is expected to benefit from the business combination. Each CGU to which goodwill is allocated represents the lowest level within the group at which the goodwill is monitored for internal management purposes.

Acquired intangible assets – customer relationships and brands

Intangible assets such as customer relationships or brands acquired through business combinations are recorded at fair value at the date of acquisition and subsequently carried at amortised cost. Assumptions are used in estimating the fair values of these relationships or brands and include management’s estimates of revenue and profits to be generated by them.

Telecommunications licences

Licence fees paid to governments, which permit telecommunications activities to be operated for defined periods, are initially recorded at cost and amortised from the time the network is available for use to the end of the licence period or where our usage can extend beyond the initial licence period, over the period we expect to benefit from the use of the licences, which is typically 20 years. Licences acquired through business combinations are recorded at fair value at the date of acquisition and subsequently carried at amortised cost. The fair value is based on management’s assumption of future cash flows using market expectations at acquisition date.

Computer software

Computer software comprises computer software licences purchased from third parties, and also the cost of internally developed software. Computer software licences purchased from third parties are initially recorded at cost.

Costs directly associated with the production of internally developed software, including direct and indirect labour costs of development, are capitalised only where it is probable that the software will generate future economic benefits, the cost of the asset can be reliably measured and technical feasibility can be demonstrated, in which case it is capitalised as an intangible asset on the balance sheet. Costs which do not meet these criteria and research costs are expensed as incurred.

The group’s development costs which give rise to internally developed software include upgrading the network architecture or functionality and developing service platforms aimed at offering new services to the group’s customers. See research and development on page 17.

Other

Other intangible assets include website development costs and other licences. Items are capitalised at cost and amortised on a straight line basis over their useful economic life or the term of the contract.

Estimated useful economic lives

The estimated useful economic lives assigned to the principal categories of intangible assets are as follows:

–  Computersoftware	2to10years
–  Telecommunicationslicences	2to20years
–  Customerrelationshipsandbrands	1to15years

Programme rights

Programme rights are recognised on the balance sheet from the point at which the legally enforceable licence period begins. Rights for which the licence period has not started are disclosed as contractual commitments in note 29. Payments made to receive commissioned or acquired programming in advance of the legal right to broadcast the programmes are classified as prepayments.

Programmes produced internally are charged to the income statement over the period of the related broadcast.

Programme rights are tested for impairment in accordance with the group’s policy for impairment of non-financial assets set out below. Related cash outflows are classified as operating cash flows in the cash flow statement.

Inventories

Inventories

Network maintenance equipment and equipment to be sold to customers are stated at the lower of cost or net realisable value, taking into account expected revenues from the sale of packages comprising a mobile handset and a subscription. Cost corresponds to purchase or production cost determined by either the first in first out (FIFO) or average cost method.

Provisions

Provisions

Provisions are recognised when the group has a present legal or constructive obligation as a result of past events, it is probable that an outflow of resources will be required to settle the obligation and the amount can be reliably estimated. Provisions are determined by discounting the expected future cash flows at a pre-tax rate that reflects current market assessments of the time value of money and the risks specific to the liability. Financial liabilities within provisions are initially recognised at fair value and subsequently carried at amortised cost using the effective interest method. Onerous lease provisions are measured at the lower of the cost to fulfil or to exit the contract.

Current and deferred income tax

Current and deferred income tax

Current income tax is calculated on the basis of the tax laws enacted or substantively enacted at the balance sheet date in the countries where the group’s subsidiaries, associates and joint ventures operate and generate taxable income. The group periodically evaluates positions taken in tax returns with respect to situations in which applicable tax regulation is subject to interpretation, and the group establishes provisions where appropriate on the basis of the amounts expected to be paid to tax authorities.

Deferred tax is recognised, using the liability method, in respect of temporary differences between the carrying amount of the group’s assets and liabilities and their tax base. Deferred income tax assets and liabilities are offset when there is a legally enforceable right to offset current tax assets against current tax liabilities and when the deferred income tax assets and liabilities relate to income taxes levied by the same taxation authority on either the taxable entity or different taxable entities where there is an intention to settle the balances on a net basis. Any remaining deferred tax asset is recognised only when, on the basis of all available evidence, it can be regarded as probable that there will be suitable taxable profits, within the same jurisdiction, in the foreseeable future against which the deductible temporary difference can be utilised.

Deferred tax is determined using tax rates that are expected to apply in the periods in which the asset is realised or liability settled, based on tax rates and laws that have been enacted or substantively enacted by the balance sheet date.

Impairment of non-financial assets

Impairment of non-financial assets

Intangible assets with finite useful lives and property, plant and equipment are tested for impairment if events or changes in circumstances (assessed at each reporting date) indicate that the carrying amount may not be recoverable. When an impairment test is performed, the recoverable amount is assessed by reference to the higher of the net present value of the expected future cash flows (value in use) of the relevant cash generating unit and the fair value less costs to dispose.

Goodwill is reviewed for impairment at least annually. Impairment losses are recognised in the income statement, as a specific item. If a cash generating unit is impaired, impairment losses are allocated firstly against goodwill, and secondly on a pro-rata basis against intangible and other assets.

Government grants

Government grants

Government grants are recognised when there is reasonable assurance that the conditions associated with the grants have been complied with and the grants will be received.

Grants for the purchase or production of property, plant and equipment are deducted from the cost of the related assets and reduce future depreciation expense accordingly. Grants for the reimbursement of operating expenditure are deducted from the related category of costs in the income statement. Government grants received relating to the BDUK programme and other rural superfast broadband contracts are accounted for as described under ‘Critical accounting estimates and key judgements’.

Once a government grant is recognised, any related deferred income is treated in accordance with IAS 20 ‘Accounting for Government Grants and Disclosure of Government Assistance’.

Foreign currencies

Foreign currencies

Foreign currency transactions are translated into the functional currency using the exchange rates prevailing at the date of the transaction. Foreign exchange gains and losses resulting from the settlement of transactions and the translation of monetary assets and liabilities denominated in foreign currencies at period end exchange rates are recognised in the income statement line which most appropriately reflects the nature of the item or transaction.

On consolidation, assets and liabilities of foreign undertakings are translated into Sterling at year end exchange rates. The results of foreign undertakings are translated into Sterling at average rates of exchange for the year (unless this average is not a reasonable approximation of the cumulative effects of the rates prevailing on the transaction dates, in which case income and expenses are translated at the dates of the transactions). Foreign exchange differences arising on the retranslation of foreign undertakings are recognised directly in a separate component of equity, the translation reserve.

In the event of the disposal of an undertaking with assets and liabilities denominated in a foreign currency, the cumulative translation difference associated with the undertaking in the translation reserve is charged or credited to the gain or loss on disposal recognised in the income statement.

Research and development

Research and development

Research expenditure is recognised in the income statement in the period in which it is incurred. Development expenditure, including the cost of internally developed software, is recognised in the income statement in the period in which it is incurred unless it is probable that economic benefits will flow to the group from the asset being developed, the cost of the asset can be reliably measured and technical feasibility can be demonstrated, in which case it is capitalised as an intangible asset on the balance sheet. Capitalisation ceases when the asset being developed is ready for use. Research and development costs include direct and indirect labour, materials and directly attributable overheads.

Leases

Leases

The determination of whether an arrangement is, or contains, a lease is based on the substance of the arrangement and requires an assessment of whether the fulfilment of the arrangement is dependent on the use of a specific asset or assets and whether the arrangement conveys the right to use the asset.

Leases of property, plant and equipment where the group holds substantially all the risks and rewards of ownership are classified as finance leases. Finance lease assets are capitalised at the commencement of the lease term at the lower of the present value of the minimum lease payments or the fair value of the leased asset. The obligations relating to finance leases, net of finance charges in respect of future periods, are recognised as liabilities. Leases are subsequently measured at amortised cost using the effective interest method.

Leases where a significant portion of the risks and rewards are held by the lessor are classified as operating leases. Rentals are charged to the income statement on a straight line basis over the period of the lease.

Share-based payments

Share-based payments

BT Group plc operates a number of equity settled share-based payment arrangements, under which the group receives services from employees in consideration for equity instruments (share options and shares) of BT Group plc. Equity settled share-based payments are measured at fair value at the date of grant. Market-based performance criteria and non-vesting conditions (for example, the requirement for employees to make contributions to the share purchase programme) are reflected in this measurement of fair value. The fair value determined at the grant date is recognised as an expense on a straight line basis over the vesting period, based on the group’s estimate of the options or shares that will eventually vest and adjusted for the effect of non market-based vesting conditions. Fair value is measured using either the Binomial options pricing model or Monte Carlo simulations, whichever is more appropriate to the share-based payment arrangement.

Service and performance conditions are vesting conditions. Any other conditions are non-vesting conditions which have to be taken into account to determine the fair value of equity instruments granted. In the case that an award or option does not vest as a result of a failure to meet a non-vesting condition that is within the control of either counterparty, this is accounted for as a cancellation. Cancellations are treated as accelerated vesting and all remaining future charges are immediately recognised in the income statement. As the requirement to save under an employee saveshare arrangement is a non-vesting condition, employee cancellations, other than through a termination of service, are treated as an accelerated vesting.

No adjustment is made to total equity for awards that lapse or are forfeited after the vesting date.

Termination benefits

Termination benefits

Termination benefits (leaver costs) are payable when employment is terminated before the normal retirement date, or when an employee accepts voluntary redundancy in exchange for these benefits. The group recognises termination benefits when it is demonstrably committed to the affected employees leaving the group.

Financial instruments

THE STRATEGIC REPORT GOVERNANCE FINANCIALSTATEMENTS ADDITIONAL INFORMATION

Financial instruments

Financial liabilities at amortised cost

Trade and other payables

Financial liabilities within trade and other payables are initially recognised at fair value, which is usually the original invoiced amount, and subsequently carried at amortised cost using the effective interest method.

Loans and other borrowings

Loans and other borrowings are initially recognised at the fair value of amounts received net of transaction costs. Loans and other borrowings are subsequently measured at amortised cost using the effective interest method and, if included in a fair value hedge relationship, are re-valued to reflect the fair value movements on the hedged risk associated with the loans and other borrowings. The resulting amortisation of fair value movements, on de-designation of the hedge, is recognised in the income statement.

Available-for-sale investments

Liquid and other investments are classified as available-for-sale investments and are initially recognised at fair value plus direct transaction costs. These are re-measured at subsequent reporting dates to fair value, with unrealised gains and losses (except for changes in exchange rates for monetary items, interest, dividends and impairment losses, which are recognised in the income statement) recognised in equity. When the financial asset is derecognised, at which time the cumulative gain or loss previously recognised in equity is taken to the income statement, in the line that most appropriately reflects the nature of the item or transaction. On disposal or impairment of the investments, any gains and losses that have been deferred in other comprehensive income are re-classified to the income statement. Dividends on equity investments are recognised in the income statement when the group’s right to receive payment is established. Equity investments are recorded in non-current assets unless they are expected to be sold within one year.

Loans and receivables

Trade and other receivables

Trade and other receivables are initially recognised at fair value, which is usually the original invoiced amount, and are subsequently carried at amortised cost, using the effective interest method, less provisions made for doubtful receivables. Provisions are made specifically where there is evidence of a risk of non-payment, taking into account ageing, previous losses experienced and general economic conditions.

Cash and cash equivalents

Cash and cash equivalents comprise cash in hand and current balances with banks and similar institutions, which are readily convertible to cash and are subject to insignificant risk of changes in value and have an original maturity of three months or less. For the purpose of the consolidated cash flow statement, cash and cash equivalents are as defined above net of outstanding bank overdrafts. Bank overdrafts are included within loans and other borrowings, in current liabilities on the balance sheet.

Financial assets and liabilities at fair value through profit or loss

All of the group’s derivative financial instruments are held for trading and classified as fair value through profit or loss.

Derivative financial instruments

The group uses derivative financial instruments mainly to reduce exposure to foreign exchange and interest rate risks. The group’s policy is not to use derivatives for trading purposes. However, derivatives that do not qualify for hedge accounting or are specifically not designated as a hedge where natural offset is more appropriate are initially recognised and subsequently measured at fair value through profit and loss. Any direct transaction costs are recognised immediately in the income statement. Gains and losses on re-measurement are recognised in the income statement in the line that most appropriately reflects the nature of the item or transaction to which they relate. Derivative financial instruments are classified as current assets or current liabilities where they have a maturity period within 12 months. Where derivative financial instruments have a maturity period greater than 12 months, they are classified within either non-current assets or non-current liabilities.

Where the fair value of a derivative contract at initial recognition is not supported by observable market data and differs from the transaction price, a day one gain or loss will arise which is not recognised in the income statement. Such gains and losses are deferred and amortised to the income statement based on the remaining contractual term and as observable market data becomes available.

Hedge accounting

Where derivatives qualify for hedge accounting, recognition of any resultant gain or loss depends on the nature of the hedge. To qualify for hedge accounting, hedge documentation must be prepared at inception and the hedge must be expected to be highly effective both prospectively and retrospectively. The hedge is tested for effectiveness at inception and in subsequent periods in which the hedge remains in operation. Hedge accounting is discontinued when the hedging instrument expires, or is sold, terminated or no longer qualifies for hedge accounting or the group chooses to end the hedge relationship. The group designates certain derivatives as either cash flow hedges or fair value hedges.

Cash flow hedges

When a derivative financial instrument is designated as a hedge of the variability in cash flows of a recognised asset or liability, or a highly probable transaction, the effective part of any gain or loss on the derivative financial instrument is recognised directly in equity, in the cash flow reserve. For cash flow hedges of recognised assets or liabilities, the associated cumulative gain or loss is removed from equity and recognised in the same line of the income statement and in the same period or periods that the hedged transaction affects the income statement. Any ineffectiveness arising on a cash flow hedge of a recognised asset or liability is recognised immediately in the same income statement line as the hedged item. Where ineffectiveness arises on highly probable transactions, it is recognised in the income statement line which most appropriately reflects the nature of the item or transaction.

Fair value hedges

When a derivative financial instrument is designated as a hedge of the variability in fair value of a recognised asset or liability, or unrecognised firm commitment, the change in fair value of the derivative that is designated as a fair value hedge is recorded in the income statement at each reporting date, together with any changes in fair value of the hedged asset or liability that is attributable to the hedged risk.

British Telecommunications plc Annual Report & Form 20-F 2018 1

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Significant accounting policies (Tables)

12 Months Ended

Mar. 31, 2018

Significant Accounting Policies [Abstract]

Summary of Estimated Useful Lives Assigned to Principal Categories of Assets

The estimated useful lives assigned to principal categories of assets are as follows:

Land and buildings
–  Freehold buildings	14 to 50 years
–  Short-term leasehold improvements				Shorter of 10 years or lease term
–  Leasehold land and buildings		Unexpired portion of lease or 40 years, whichever is the shorter
Network infrastructure
Transmission equipment
–  Duct		40 years
–  Cable		3 to 25 years
–  Fibre		5 to 20 years
Exchange equipment		2 to 13 years
Other network equipment		2 to 20 years
Other assets
–  Motor vehicles		2 to 9 years
–  Computers and office equipment			3 to 7 years

Summary of Estimated Useful Economic Lives Assigned to Principal Catagories of Intangible Assets

The estimated useful economic lives assigned to the principal categories of intangible assets are as follows:

–  Computersoftware	2to10years
–  Telecommunicationslicences	2to20years
–  Customerrelationshipsandbrands	1to15years

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Segment information (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Operating Segments [Abstract]

Summary of Results of Reportable Segments

We have set out below information regarding the results of each reportable segment.

Segment revenueandprofit

Year ended 31 March 2018	BT Consumer £m			EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		5,066			5,294			4,563			5,013			2,009			5,123			8			27,076
Internal revenue		(66	)		(37	)		(115	)		–			(134	)		(2,978	)		–			(3,330	)
Revenue from external customersa		5,000			5,257			4,448			5,013			1,875			2,145			8			23,746
EBITDAb		1,023			1,353			1,418			434			754			2,520			6			7,508
Depreciation and amortisation		(216	)		(776	)		(365	)		(424	)		(311	)		(1,360	)		(62	)		(3,514	)
Operating profit (loss)a		807			577			1,053			10			443			1,160			(56	)		3,994
Specific items (note 8)																							(610	)
Operating profit																							3,384
Net finance expensec																							(579	)
Share of post tax profit (loss) of associates and joint ventures																							(1	)
Profit before tax																							2,804

Year ended 31 March 2017	BT Consumer £m			EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		4,934			5,090			4,758			5,479			2,109			5,098			10			27,478
Internal revenue		(63	)		(37	)		(122	)		–			(138	)		(3,036	)		–			(3,396	)
Revenue from external customersa		4,871			5,053			4,636			5,479			1,971			2,062			10			24,082
EBITDAb		1,012			1,156			1,528			495			834			2,633			(10	)		7,648
Depreciation and amortisation		(209	)		(780	)		(352	)		(439	)		(306	)		(1,369	)		(55	)		(3,510	)
Operating profit (loss)a		803			376			1,176			56			528			1,264			(65	)		4,138
Specific items (note 8)																							(968	)
Operating profit																							3,170
Net finance expensec																							(610	)
Share of post tax profit (loss) of associates and joint ventures																							(9	)
Profit before tax																							2,551

Year ended 31 March 2016	BT Consumer £m			EE £m		d	Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		4,608			841			4,294			5,074			2,274			5,100			11			22,202
Internal revenue		(65	)		(7	)		(99	)		–			(94	)		(3,058	)		–			(3,323	)
Revenue from external customersa		4,543			834			4,195			5,074			2,180			2,042			11			18,879
EBITDAb		1,055			173			1,414			479			755			2,659			(77	)		6,458
Depreciation and amortisation		(207	)		(146	)		(284	)		(422	)		(253	)		(1,301	)		(18	)		(2,631	)
Operating profit (loss)a		848			27			1,130			57			502			1,358			(95	)		3,827
Specific items (note 8)																							(212	)
Operating profit																							3,615
Net finance expensec																							(380	)
Share of post tax profit (loss) of associates and joint ventures																							6
Profit before tax																							3,241

^a Before specific items.

^b EBITDA is stated before specific items and is the group’s profitability measure for segments.

^c Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m). See note 8.

^d EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Summary of Internal Revenue and Costs Recorded by Each Reportable Segment

The tables below show internal revenue and costs recorded by each reportable segment.

	Internal cost recorded by
Year ended 31 March 2018	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–		24		20		4		–		18		66
EE		–		–		–		–		37		–		–		37
Business and Public Sector		62		2		–		32		19		–		–		115
Global Services		–		–		–		–		–		–		–		–
Wholesale and Ventures		1		2		13		10		–		42		66		134
Openreach		896		–		210		125		232		–		1,515		2,978
Total		959		4		247		187		292		42		1,599		3,330

	Internal cost recorded by
Year ended 31 March 2017	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–	21		20		4			–	18		63
EE		–		–		–		–		37		–		–		37
Business and Public Sector		60		3		–		39		20		–		–		122
Global Services		–		–		–		–		–		–		–		–
Wholesale and Ventures		–		–		2		23		–		39		74		138
Openreach		910		–		236		158		260		–		1,472		3,036
Total		970		3		259		240		321		39		1,564		3,396

	Internal cost recorded by
Year ended 31 March 2016	BT Consumer £m		EE £m		a	Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–			20		23		4		–		18		65
EEa		–		–			–		–		7		–		–		7
Business and Public Sector		60		1			–		18		19		1		–		99
Global Services		–		–			–		–		–		–		–		–
Wholesale and Ventures		–		12			5		22		–		55		–		94
Openreach		905		–			262		173		264		–		1,454		3,058
Total		965		13			287		236		294		56		1,472		3,323

^a EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Summary of Revenue by Products and Services

Year ended 31 March	2018 £m		2017 £m		2016 £m
ICT and managed networks		5,530		5,927		6,193
Broadband and TV		4,655		4,477		3,535
Mobile		6,451		6,358		1,326
Calls, lines and connections		5,126		5,069		5,920
Transit		265	404		419
Other products and services		1,719		1,847		1,486
Revenuea		23,746		24,082		18,879

^a Before specific items.

Summary of Capital Expenditure

Capital expenditure

Year ended 31 March 2018	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Intangible assets		106		130		93		92		87		70		64		642
Property, plant and equipment		185		498		211		186		142		1,588		70		2,880
Capital expenditurea		291		628		304		278		229		1,658		134		3,522

Year ended 31 March 2017	BT Consumer £m	EE £m	Business and Public Sector £m	Global Services £m	Wholesale and Ventures £m	Openreach £m		Other £m	Total £m
Intangible assets	92	133	64	126	77	74		55	621
Property, plant and equipment	145	483	211	235	149		1,499	111		2,833
Capital expenditurea	237	616	275	361	226		1,573	166		3,454

Year ended 31 March 2016	BT Consumer £m	EE £m	b	Business and Public Sector £m	Global Services £m	Wholesale and Ventures £m	Openreach £m		Other £m	Total £m
Intangible assets	88	29		36	62	70	62		65	412
Property, plant and equipment	119	67		117	293	139		1,385	90		2,210
Capital expenditurea	207	96		153	355	209		1,447	155		2,622

^a Net of government grants.

^b EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Summary of Geographic Information by Revenue from External Customers and Non-Current Assets

Revenue from external customers

Year ended 31 March	2018 £m		2017 £m		2016 £m
UK		19,687		19,421		14,814
Europe, Middle East and Africa, excluding the UK		2,489		2,841		2,442
Americas		996		1,148		1,011
Asia Pacific		574		672		612
Revenuea		23,746		24,082		18,879

^a Before specific items.

Non-current assets

At 31 March	2018 £m		2017 £m		2016 £m
UK		28,843		28,818		28,583
Europe, Middle East and Africa, excluding the UK		2,527		2,535		2,349
Americas		331		424		548
Asia Pacific		109		149		191
Non-current assets		31,810		31,926		31,671

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Operating Costs (Tables)

12 Months Ended

Mar. 31, 2018

Operating Costs [Abstract]

Summary of Operating Costs

Year ended 31 March	Notes	2018 £m			2017 £m			2016 £m
Operating costs by nature
Staff costs:
Wages and salaries			4,223			4,128			3,684
Social security costs			461			477			398
Other pension costs	19		624			521			494
Share-based payment expense	20		84			57			58
Total staff costs			5,392			5,183			4,634
Own work capitalised			(798	)		(813	)		(720	)
Net staff costs			4,594			4,370			3,914
Net indirect labour costsa			315			399			304
Net labour costs			4,909			4,769			4,218
Payments to telecommunications operators			2,306			2,653			2,183
Property and energy costs			1,285			1,202			1,024
Network operating and IT costs			963			983			644
TV programme rights charges			763			714			544
Other operating costs			6,234			6,298			4,023
Other operating income			(222	)		(185	)		(215	)
Depreciation of property, plant and equipment
Owned assets	12		2,381			2,382			2,000
Held under finance leases	12		10			10			10
Amortisation of intangible assetsb	11		1,123			1,118			621
Total operating costs before specific items			19,752			19,944			15,052
Specific items	8		587			948			345
Total operating costs			20,339			20,892			15,397
Operating costs before specific items include the following:
Leaver costsc			50			86			109
Research and development expenditured			632			638			574
Operating lease charges			732			692			441
Foreign currency gains			–			(12	)		(1	)
Government grants			(3	)		(5	)		(6	)

^a Net of capitalised indirect labour costs of £612m (2016/17: £463m, 2015/16: £430m).

^b Excludes £nil (2016/17: £62m, 2015/16: £nil) of amortisation presented as specific items which relate to a write off of software costs as a result of the integration of EE. Refer to note 8.

^c Leaver costs are included within wages and salaries, except for leaver costs of £168m (2016/17: £37m, 2015/16: £nil) associated with restructuring and EE integration costs, which have been recorded as specific items.

^d Research and development expenditure reported in the income statement, includes amortisation of £573m (2016/17: £577m, 2015/16: £501m) in respect of internally developed computer software and operating expenses of £59m (2016/17: £61m, 2015/16: £73m). In addition, the group capitalised software development costs of £450m (2016/17: £457m, 2015/16: £399m).

Summary of Compensation of Key Management Personnel

Compensation of key management personnel is shown in the table below:

Year ended 31 March	2018 £m		2017 £m		2016 £m
Short-term employee benefits	12.4			10.9		10.3
Post employment benefits	1.4			1.4		1.2
Share-based payments	6.6			5.8		5.9
Termination benefits		2.2		–		0.6
	22.6			18.1		18.0

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Employees (Tables)

12 Months Ended

Mar. 31, 2018

Employees [Abstract]

Summary of Number of Employees in the Group

		2018		2017		2016
Number of employees in the groupa	Year end 000	Average 000	Year end 000	Average 000	Year end 000	Average 000
UK	82.2	82.5	82.8	82.2	81.4	71.8
Non-UK	23.6	23.7	23.6	22.8	21.1	19.2
Total employees	105.8	106.2	106.4	105.0	102.5	91.0

		2018		2017		2016
Number of employees in the groupa	Year end 000	Average 000	Year end 000	Average 000	Year end 000	Average 000
BT Consumer	8.8	8.8	8.7	7.7	6.7	6.3
EE	9.4	9.2	9.2	9.1	9.0	1.3
Business and Public Sector	10.1	10.3	10.3	10.2	10.3	9.3
Global Services	16.9	17.3	17.5	17.4	16.8	16.5
Wholesale and Ventures	3.8	3.9	3.8	3.7	3.7	3.8
Openreach	30.5	30.4	30.2	30.9	31.5	32.1
Other	26.3	26.3	26.7	26.0	24.5	21.7
Total employees	105.8	106.2	106.4	105.0	102.5	91.0

^a These reflect the full-time equivalent of full and part-time employees.

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Audit, audit related and other non-audit services (Tables)

12 Months Ended

Mar. 31, 2018

Non Audit Fees [Abstract]

Summary of Fees Paid or Payable to Company's Auditors

The following fees were paid or are payable to the company’s auditors, PricewaterhouseCoopers LLP and other firms in the PricewaterhouseCoopers network.

Year ended 31 March	2018 £000		2017 £000		2016 £000
Fees payable to the company’s auditors and its associates for:
Audit servicesa
The audit of the parent company and the consolidated financial statements		5,372		4,271		3,871
The audit of the company’s subsidiaries		5,866		5,664		5,073
		11,238		9,935		8,944
Audit related assurance servicesb		1,631		1,865		2,210
Other non-audit services
Taxation compliance servicesc		–		366		412
Taxation advisory servicesd		–		111		156
All other assurance servicese		211		200		1,611
All other servicesf		592		2,332		1,665
		803		3,009		3,844
Total services		13,672		14,809		14,998

^a Services in relation to the audit of the parent company and the consolidated financial statements, including fees for reports under section 404 of the Sarbanes-Oxley Act. This also includes fees payable for the statutory audits of the financial statements of subsidiary companies.

^b Services in relation to other statutory filings or engagements that are required by law or regulation to be carried out by an appointed auditor. This includes fees for the review of interim results, the audit of the group’s regulatory financial statements and reporting associated with the group’s US debt shelf registration.

^c Services relating to tax returns, tax audits, monitoring and enquiries.

^d Fees payable for all taxation advisory services not falling within taxation compliance.

^e All other assurance services include fees payable to PricewaterhouseCoopers LLP as Reporting Accountants in 2015/16 in relation to the Listing Prospectus, which was issued on 26 January 2016 for the issue of new shares.

^f Fees payable for all non-audit services not covered above, principally comprising other advisory services.

Summary of Total Fees Received by Company's Auditors from the BT Pension Scheme

Intheyear ended 31 March 2018 PricewaterhouseCoopers LLPreceived total fees from the BTPension Schemeof £2.1m (2016/17: £2.1m, 2015/16:£1.7m) in respect ofthefollowingservices:

Year ended 31 March	2018 £000		2017 £000		2016 £000
Audit of financial statements of associates		345		251		213
Audit-related assurance services		–		–		10
Taxation compliance services		153		210		198
Taxation advisory services		1,074		493		681
Other non-audit services		565		1,168		603
Total services		2,137		2,122		1,705

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Specific items (Tables)

12 Months Ended

Mar. 31, 2018

Specific Items [Abstract]

Summary of Specific Items

Year ended 31 March	2018 £m			2017 £m			2016 £m
Revenue
Italian business investigation		–			22			–
Regulatory matters		23			(2	)		(203	)
EE fair value adjustment		–			–			70
		23			20			(133	)
Operating costs
EE acquisition warranty claims		225			–			–
Restructuring charges		241			–			–
EE acquisition and integration costs		46			215			113
Property rationalisation costs		28			–			29
Regulatory matters		26			481			203
Italian business investigation		22			238			–
Out of period irrecoverable VAT		–			30			–
Profit on disposal of businesses		(1	)		(16	)		–
		587			948			345
Operating loss		610			968			212
Net finance expense
Interest expense on retirement benefit obligation		218			209			221
EE related finance cost		–			–			8
Interest on out of period irrecoverable VAT		–			1			–
		218			210			229
Net specific items charge before tax		828			1,178			441
Taxation
Tax credit on specific items above		(87	)		(154	)		(70	)
Tax credit on re-measurement of deferred tax		–			(63	)		(96	)
		(87	)		(217	)		(166	)
Net specific items charge after tax		741			961			275

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Taxation (Tables)

12 Months Ended

Mar. 31, 2018

Taxation [Abstract]

Analysis of Our Taxation Expenses

Analysisofourtaxationexpensefortheyear

Year ended 31 March	2018 £m			2017 £m			2016 £m
United Kingdom
Corporation tax at 19% (2016/17: 20%, 2015/16: 20%)		(614	)		(594	)		(684	)
Adjustments in respect of earlier years		37			33			59
Non-UK taxation
Current		(66	)		(109	)		(80	)
Adjustments in respect of earlier years		23			–			29
Total current tax expense		(620	)		(670	)		(676	)
Deferred taxation
Origination and reversal of temporary differences		46			96			70
Adjustments in respect of earlier years		(57	)		26			2
Impact of change in UK corporation tax rate to 17% (2016/17: 17%, 2015/16: 19%)		–			63			96
Remeasurement of temporary differences		11			–			–
Total deferred taxation credit		–			185			168
Total taxation expense		(620	)		(485	)		(508	)

Summary of Factors Affecting Our Taxation Expense for the Year

Thetaxationexpense on the profitforthe year differs fromtheamount computed byapplying theUK corporation taxrate totheprofit beforetaxation as a result ofthefollowingfactors:

Year ended 31 March	2018 £m			2017 £m			2016 £m
Profit before taxation		2,804			2,551			3,241
Expected taxation expense at UK rate of 19% (2016/17: 20%, 2015/16: 20%)		(533	)		(510	)		(648	)
Effects of:
(Higher) lower taxes on non-UK profits		(8	)		(29	)		4
Net permanent differences between tax and accountinga		(100	)		(183	)		(12	)
Adjustments in respect of earlier yearsb		3			59			90
Prior year non-UK losses used against current year profits		16			120			9
Non-UK losses not recognisedc		(9	)		(8	)		(34	)
Other deferred tax assets not recognised		–			–			6
Lower taxes on profit on disposal of business		–			3			–
Re-measurement of deferred tax balances		11			63			96
Other non-recurring items		–			–			(19	)
Total taxation expense		(620	)		(485	)		(508	)
Exclude specific items (note 8)		(87	)		(217	)		(166	)
Total taxation expense before specific items		(707	)		(702	)		(674	)

^a Includes income that is not taxable or UK income taxable at a different rate, and expenses for which no tax relief is received. Examples include some types of depreciation and amortisation and the benefit of R&D tax incentives.

^b Reflects the differences between initial accounting estimates and tax returns submitted to tax authorities, including the release and establishment of provisions for uncertain tax positions.

^c Reflects lossesmadeincountrieswhereit hasnotbeenconsideredappropriateto recogniseadeferredtaxasset,asfuturetaxableprofitsarenotprobable.

Summary of Tax Components of Other Comprehensive Income

Taxcomponentsofothercomprehensiveincome

Year ended 31 March	2018 Tax credit (expense) £m			2017 Tax credit (expense) £m			2016 Tax credit (expense) £m
Tax on items that will not be reclassified to the income statement
Pension remeasurements		(346	)		416			(240	)
Tax on items that have been or may be reclassified subsequently to the income statement
Exchange differences on translation of foreign operations		(9	)		21			38
Fair value movements on cash flow hedges
– net fair value gains or losses		57			(131	)		(72	)
– recognised in income and expense		(47	)		139			39
		(345	)		445			(235	)
Current tax credita		203			122			231
Deferred tax (expense) credit		(548	)		323			(466	)
		(345	)		445			(235	)

^a Includes£212m(2016/17:£110m,2015/16:£217m)relatingtocashcontributionsmadetoreduceretirementbenefitobligations.

Summary of Tax (Expense) Credit Recognised Directly in Equity

Tax(expense)creditrecogniseddirectlyinequity

Year ended 31 March	2018 £m			2017 £m			2016 £m
Tax (expense) credit relating to share-based payments		(2	)		(6	)		12

Summary of Deferred Taxation

Deferred taxation

	Fixed asset temporary differences £m			Retirement benefit obligations £m		a	Share- based payments £m			Tax losses £m			Other £m			Jurisdictional offset £m			Total £m
At 1 April 2016		1,618			(1,149	)		(54	)		(325	)		(75	)		–			15
(Credit) expense recognised in the income statement		(181	)		(82	)		14			65			(1	)		–			(185	)
(Credit) expense recognised in other comprehensive income		(5	)		(306	)		–			(3	)		(9	)		–			(323	)
Expense recognised in equity		–			–			23			–			–			–			23
Exchange differences		–			–			–			(7	)		–			–			(7	)
At 31 March 2017		1,432			(1,537	)		(17	)		(270	)		(85	)		–			(477	)
Non-current
Deferred tax asset		(117	)		(1,537	)		(17	)		(270	)		(96	)		320			(1,717	)
Deferred tax liability		1,549			–			–			–			11			(320	)		1,240
At 1 April 2017		1,432			(1,537	)		(17	)		(270	)		(85	)		–			(477	)
Expense (credit) recognised in the income statement		11			(104	)		4			89			–			–			–
Expense (credit) recognised in other comprehensive income		–			558			–			–			(10	)		–			548
Expense recognised in equity		–			–			6			–			–			–			6
Exchange differences		–			–			–			(2	)		5			–			3
Transfer to current tax		17			–			–			–			–			–			17
At 31 March 2018		1,460			(1,083	)		(7	)		(183	)		(90	)		–			97
Non-current
Deferred tax asset		(41	)		(1,083	)		(7	)		(183	)		(90	)		161			(1,243	)
Deferred tax liability		1,501			–			–			–			–			(161	)		1,340
At 31 March 2018		1,460			(1,083	)		(7	)		(183	)		(90	)		–			97

^a Includesa deferredtaxassetof£2m(2016/17:£2m)arisingon contributionspayableto definedcontributionpensionplans.

Summary of Restricted Loss

A summary of expiry dates for losses in respect ofwhich restrictionsapplyis set out below:

At 31 March 2018	£m		Expiry
Restricted losses
Europe		14	2019–2027
Americas		204	2019-2037
Other		2	2019–2027
Total restricted losses		220
Unrestricted operating losses		3,784	No expiry
Other temporary differences		77	No expiry
Total		4,081

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Intangible assets (Tables)

12 Months Ended

Mar. 31, 2018

Intangible Assets [Abstract]

Summary of Intangible Assets

	Goodwill £m			Customer relationships and brands £m			Telecoms licences and other £m			Internally developed software £m			Purchased software £m			Total £m
Cost
At 1 April 2016		7,915			3,401			2,930			4,073			1,610			19,929
Acquisitions		5			–			–			–			–			5
Additions		–			–			–			483			138			621
Disposals and adjustmentsa		(23	)		–			–			(131	)		2			(152	)
Transfers		–			–			–			(66	)		62			(4	)
Exchange differences		145			21			15			4			41			226
At 31 March 2017		8,042			3,422			2,945			4,363			1,853			20,625
Additions		–			–			–			517			125			642
Acquisitions		14			–			3			–			–			17
Disposals and adjustmentsa		(3	)		–			(3	)		(55	)		(413	)		(474	)
Exchange differences		(100	)		(12	)		6			(3	)		9			(100	)
At 31 March 2018		7,953			3,410			2,951			4,822			1,574			20,710
Accumulated amortisation
At 1 April 2016		–			418			131			2,747			1,175			4,471
Charge for the yearb		–			383			140			556			101			1,180
Disposals and adjustmentsa		–			–			–			(114	)		(7	)		(121	)
Exchange differences		–			12			9			4			33			58
At 31 March 2017		–			813			280			3,193			1,302			5,588
Charge for the yearb		–			379			141			525			78			1,123
Disposals and adjustmentsa		–			–			(3	)		(36	)		(426	)		(465	)
Exchange differences		–			(1	)		3			(2	)		9			9
At 31 March 2018		–			1,191			421			3,680			963			6,255
Carrying amount
At 31 March 2018		7,953			2,219			2,530			1,142			611			14,455
At 31 March 2017		8,042			2,609			2,665			1,170			551			15,037

^aFully depreciated assets in the group’s fixed asset registers were reviewed during the year, as part of the group’s annual asset verification exercise, and certain assets that were no longer in use have been written off, reducing cost and accumulated depreciation by £0.4bn (2016/17: £nil).

^b   Includesa £nil(2016/17: £62m)specificitemamortisationchargerelatingtothewrite-offofinternallydevelopedsoftwareasweintegratetheEEandBTITinfrastructure.

Summary of Goodwill Allocated to Cash Generating Units

TheseCGUs representthesmallestidentifiable groups ofassetsthatgenerate cash inflows thatare largely independentof thecash inflows fromother groupsof assets,and to which goodwill isallocated. From1 April 2016, we re-organised our customer-facing unitsresulting in thechange of the CGUsthat have associated goodwill.Weallocatedgoodwill to BT Consumer,EE,Business and PublicSector,Global Servicesand Wholesale and Ventures. Previouslyno goodwill was allocatedtoWholesale and Ventures.Inaddition to goodwill being allocated to this CGU for the first time, therewere changes totheamount allocated to the other CGUs asa result ofthere-organisation. Goodwill is allocated tothese CGUs as follows:

Cost	BT Consumer £m		EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m		Total £m
At 1 April 2016		1,183		4,917			662			1,153			–		7,915
Re-organisation		–		(2,149	)		1,921			(709	)		937		–
Exchange differences		–		–			10			135			–		145
Acquisitions and disposals		–		–			(23	)		–			5		(18	)
At 31 March 2017		1,183		2,768			2,570			579			942		8,042
Exchange differences		–		–			(8	)		(92	)		–		(100	)
Acquisitions and disposals		–		–			–			11			–		11
At 31 March 2018		1,183		2,768			2,562			498			942		7,953

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Property, plant and equipment (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Property Plant And Equipment [Abstract]

Summary of the Carrying Values of Software, Property, Plant and Equipment

Thecarrying values ofsoftware, property,plant andequipment are disclosed below and in note11. Theuseful lives applied to the principal categories ofassetsare disclosed on pages 115 and 116.

	Land and   buildings £m		a	Network   infrastructure £m		a	Other £m		b	Assets in course of construction £m			Total £m
Cost
At 31 March 2016		1,278			48,194			1,870			1,108			52,450
Additionsc		6			40			128			2,672			2,846
Transfers		14			2,393			(1	)		(2,402	)		4
Disposals and adjustmentsd		(45	)		(1,637	)		(106	)		30			(1,758	)
Exchange differences		49			382			47			5			483
At 31 March 2017		1,302			49,372			1,938			1,413			54,025
Additionsc		12			193			92			2,597			2,894
Transfers		36			2,793			16			(2,845	)		–
Disposals and adjustmentsd		(82	)		(1,540	)		(119	)		(48	)		(1,789	)
Exchange differences		(6	)		(35	)		(13	)		1			(53	)
At 31 March 2018		1,262			50,783			1,914			1,118			55,077
Accumulated depreciation
At 31 March 2016		750			34,287			1,513			–			36,550
Charge for the year		64			2,224			104			–			2,392
Disposals and adjustmentsd		(36	)		(1,627	)		(104	)		–			(1,767	)
Exchange differences		39			330			41			–			410
At 31 March 2017		817			35,214			1,554			–			37,585
Charge for the year		57			2,213			121			–			2,391
Disposals and adjustmentsd		(96	)		(1,613	)		(107	)		–			(1,816	)
Exchange differences		(5	)		(24	)		(10	)		–			(39	)
At 31 March 2018		773			35,790			1,558			–			38,121
Carrying amount
At 31 March 2018		489			14,993			356			1,118			16,956
Engineering stores		–			–			–			44			44
Total at 31 March 2018		489			14,993			356			1,162			17,000
At 31 March 2017		485			14,158			384			1,413			16,440
Engineering stores		–			–			–			58			58
Total at 31 March 2017		485			14,158			384			1,471			16,498

^a The carrying amount of the group’s property, plant and equipment includes an amount of £53m (2016/17: £73m) in respect of assets held under finance leases, comprising land and buildings of £42m (2016/17: £45m) and network infrastructure of £11m (2016/17: £28m). The depreciation expense on those assets in 2017/18 was £10m (2016/17: £10m), comprising land and buildings of £3m (2016/17: £3m) and network infrastructure of £7m (2016/17: £7m).

^b Other mainly comprises motor vehicles, computers and fixtures and fittings.

^c Net of grant funding of £74m (2016/17: £28m net grant deferral).

^d Fully depreciated assets in the group’s fixed asset registers were reviewed during the year, as part of the group’s annual asset verification exercise, and certain assets that were no longer in use have been written off, reducing cost and accumulated depreciation by £1.3bn (2016/17: £1.1bn).

Summary of Property Plant and Equipment

At 31 March	2018 £m		2017 £m
The carrying amount of land and buildings, including leasehold improvements, comprised:
Freehold		261	269
Leasehold		228	216
Total land and buildings		489	485

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Programme rights (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Programme Rights [Abstract]

Summary of Programme Rights

	Total £m
At 1 April 2016		225
Additions		753
Amortisation		(714	)
At 1 April 2017		264
Additions		771
Amortisation		(763	)
At 31 March 2018		272

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Inventories (Tables)

12 Months Ended

Mar. 31, 2018

Inventories [Abstract]

Summary of Inventories

At 31 March	2018 £m		2017 £m	2016 £m
Consumables		22	24	26
Work in progress		6	23	11
Finished goods		211	180	152
		239	227	189

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Trade and other receivables (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Trade And Other Receivables [Abstract]

Schedule of Trade and Other Receivables

The carrying value of assets comprising the costs of the initial set-up, transition or transformation phase of long-term networked IT services contracts is disclosed below.

At 31 March	2018 £m	2017 £m	2016 £m
Non-current
Other assetsa	317	360	218

^a Other assets includes costs relating to the initial set-up, transition or transformation phase of long-term networked IT services contracts of £145m (2016/17: £163m, 2015/16: £111m), and prepayments and leasing debtors of £172m (2016/17: £197m, 2015/16: £107m).

At 31 March	2018 £m		2017 £m		2016 £m
Current
Trade receivables		1,741		1,774		1,803
Amounts owed by ultimate parent company		15		25		9
Prepaymentsa		1,103	733		702
Accrued income		777	955			1,072
Other receivablesb	393		373		401
		4,029		3,860		3,987

^aPrepayments includes £325m (2016/17: £nil, 2015/16: £nil) in respect of the acquisition of spectrum in April 2018. The spectrum auction bidding cut across the 2017/18 and 2018/19 financial years. Whilst £325m was on deposit with Ofcom at 31 March 2018, we went on to win spectrum for a total price of £304m and the excess deposit balance has since been refunded. This will be transferred to intangible assets in 2018/19.

^bOther receivables includes assets held for sale of £nil (2016/17: £22m, 2015/16: £nil).

Summary of Trade Receivables After Deducting Allowances for Doubtful Debts

Trade receivables are stated after deducting allowances for doubtful debts, as follows:

	2018 £m			2017 £m			2016 £m
At 1 April	303			195			196
Expense	129			211			77
Utilised		(61	)		(114	)		(89	)
Exchange differences	4			11			11
At 31 March	375			303			195

Summary of Trade Receivables Past Due and Not Specifically Impaired

Trade receivables are due as follows:

					Past due and not specifically impaired
At 31 March	Not past due £m		Trade receivables specifically impaired net of provision £m		Between 0 and 3 months £m		Between 3 and 6 months £m		Between 6 and 12 months £m		Over 12 months £m		Total £m
2018		1,251		61		293		44		25		67		1,741
2017		1,184		146		292		17		41		94		1,774
2016		1,152		98		368		51		44		90		1,803

Schedule of Trade Receivables Not Past Due and Accrued Income

Trade receivables not past due and accrued income are analysed below by customer-facing unit.

	Trade receivables not past due						Accrued income
At 31 March	2018 £m		2017 £m		2016 £m		2018 £m		2017 £m		2016 £m
BT Consumer		157		128		138		86		90		83
EE		206		335		267		122		170		312
Business and Public Sector		253		200		115		134		151		146
Global Services		477		444		555		222		297		351
Wholesale and Ventures		92		75		76		145		167		99
Openreach		61		1		1		67		78		79
Other		5		1		–		1		2		2
Total		1,251		1,184		1,152		777		955		1,072

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Trade and other payables (Tables)

12 Months Ended

Mar. 31, 2018

Trade And Other Payables [Abstract]

Summary of Trade and Other Payables

At 31 March	2018 £m		2017 £m		2016 £m
Current
Trade payables		3,991		4,205		4,331
Amounts owed to parent company		50		63		70
Other taxation and social security		704		704		682
Other payables		428		648		527
Accrued expenses		492		382		418
Deferred incomea		1,525		1,474		1,435
		7,190		7,476		7,463

At 31 March	2018 £m		2017 £m		2016 £m
Non-current
Other payablesb		871		885		876
Deferred incomea		455		413		230
		1,326		1,298		1,106

^a Includes £132m (2016/17: £71m, 2015/16: £71m) current and £404m (2016/17: £375m, 2015/16: £187m) non-current liabilities relating to the Broadband Delivery UK programme, for which grants received by the group may be subject to re-investment or repayment depending on the level of take-up.

^b Other payables relate to operating lease liabilities and deferred gains on a 2001 sale and finance leaseback transaction.

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Provisions (Tables)

12 Months Ended

Mar. 31, 2018

Provisions [Abstract]

Details of Estimate of the Provisions

The outcome of our estimate of the provisions is disclosed below.

	Restructuring £m		a	Property £m			Network ARO £m			Network share £m			Regulatory £m			Litigation £m			Other £m			Total £m
At 31 March 2016		20			296			78			60			64			73			152			743
Income statement expense	–				38			27			5			426			6			34			536
Unwind of discount	–				12			2			2		–			–			–				16
Utilised or released		(10	)		(54	)		(24	)		(17	)		(11	)		(11	)		(8	)		(135	)
Transfers	–			–			–			–			–			–				(3	)		(3	)
Exchange  differences		1			–			–			–			–		1				2			4
At 31 March 2017		11			292			83			50			479			69			177			1,161
Income statement expense	4				37			2		–				51			6			33			133
Unwind of discount	–				11			2			2		–			–			–				15
Utilised or released		(2	)		(46	)		(16	)		(19	)		(210	)		(11	)		(32	)		(336	)
Transfers	–			–			–			–			–			–				85			85
Exchange  differences		(1	)	–			–			–			–			–				(2	)		(3	)
At 31 March 2018		12			294			71			33			320			64			261			1,055

^a  Restructuring costs for which the timing and amount are certain. These amounts are reflected in trade and other payables.

Details of Provisions

At 31 March	2018 £m		2017 £m		2016 £m
Analysed as:
Current		603		625		178
Non-current		452		536		565
		1,055		1,161		743

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Retirement Benefit Plans (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Defined Benefit Plans [Line Items]

Summary of Expense or Income from Retirement Benefit Arrangements Recognised in Income Statement

The expense or income arising from all group retirement benefit arrangements recognised in the group income statement is shown below.

Year ended 31 March	2018 £m			2017 £m		2016 £m
Recognised in the income statement before specific items
Service cost (including administration expenses & PPF levy):
– defined benefit plans		376			281		301
– defined contribution plans		265			240		193
Past service credita		(17	)		–		–
Total operating expense		624			521		494
Net interest expense on pensions deficit included in specific items (note 8)		218			209		221
Total recognised in the income statement		842			730		715

^a Past service credit primarily relates to pension plans operating outside the UK which were closed to future accrual during the year.

Summary of Pension Obligation in Respect of Defined Benefit Plans Reported in Balance Sheet

The net pension obligation in respect of defined benefit plans reported in the group balance sheet is set out below.

	2018								2017
At 31 March	Assets £m		Present value of liabilities £m			Deficit £m			Assets £m		Present value of liabilities £m			Deficit £m
BTPS		49,894		(55,783	)		(5,889	)		50,090		(58,649	)		(8,559	)
EEPS		763		(920	)		(157	)		748		(973	)		(225	)
Other plansa		299		(624	)		(325	)		274		(578	)		(304	)
Retirement benefit obligation		50,956		(57,327	)		(6,371	)		51,112		(60,200	)		(9,088	)
Adjustments due to effect of asset ceiling (IFRIC 14)							–								–
Deferred tax asset							1,081								1,535
Net pension obligation							(5,290	)							(7,553	)

^aIncluded in the present value of obligations of other plans is £97m (2016/17: £104m) related to unfunded pension arrangements.

Summary of Movements on Pension Assets and Liabilities

The table below shows the movements on the pension assets and liabilities and shows where they are reflected in the financial statements.

	Assets £m			Liabilities £m			Deficit £m
At 31 March 2016		43,968			(50,350	)		(6,382	)
Service cost (including administration expenses and PPF levy)		(44	)		(237	)		(281	)
Interest on pension deficit		1,413			(1,622	)		(209	)
Included in the group income statement								(490	)
Return on plan assets above the amount included in the group income statement		7,475			–			7,475
Actuarial loss arising from changes in financial assumptionsa		–			(10,221	)		(10,221	)
Actuarial loss arising from changes in demographic assumptionsa		–			(206	)		(206	)
Actuarial gain arising from experience adjustmentsb		–			163			163
Included in the group statement of comprehensive income								(2,789	)
Regular contributions by employer		313			–			313
Deficit contributions by employer		274			–			274
Included in the group cash flow statement								587
Contributions by employees		8			(8	)		–
Benefits paid		(2,315	)		2,315			–
Foreign exchange		20			(34	)		(14	)
Other movements								(14	)
At 31 March 2017		51,112			(60,200	)		(9,088	)
Service cost (including administration expenses and PPF levy)		(67	)		(309	)		(376	)
Past service credit		–			17			17
Interest on pension deficit		1,201			(1,419	)		(218	)
Included in the group income statement								(577	)
Return on plan assets above the amount included in the group income statement		10			–			10
Actuarial gain arising from changes in financial assumptionsa		–			2,251			2,251
Actuarial loss arising from changes in demographic assumptionsa		–			(221	)		(221	)
Actuarial gain arising from experience adjustmentsb		–			120			120
Included in the group statement of comprehensive income								2,160
Regular contributions by employer		264			–			264
Deficit contributions by employer		872			–			872
Included in the group cash flow statement								1,136
Contributions by employees		2			(2	)		–
Benefits paid		(2,449	)		2,449			–
Foreign exchange		11			(13	)		(2	)
Other movements								(2	)
At 31 March 2018		50,956			(57,327	)		(6,371	)

^aThe actuarial gain or loss arises from changes in the assumptions used to value the defined benefit liabilities at the end of the year compared with the assumptions used at the start of the year. This includes both financial assumptions, which are based on market conditions at the year end, and demographic assumptions such as life expectancy.

^bThe actuarial loss or gain arising from experience adjustments on defined benefit liabilities represents the impact on the liabilities of differences between actual experience during the year compared with the assumptions made at the start of the year. Such differences might arise, for example, from members choosing different benefit options at retirement, actual salary increases being different from those assumed or actual benefit increases being different to the pension increase assumption.

Summary of Analysis of Membership

The membership is analysed below.

Analysis of BTPS

	Active members		Deferred members		Pensioners		Total
Sections A and B liabilities (£bn)a		4.9		4.3		29.6		38.8
Section C liabilities (£bn)		7.7		5.7		3.6		17.0
Total IAS 19 liabilities (£bn)		12.6		10.0		33.2		55.8
Total number of members		30,000		60,500		202,500		293,000

^aSections A and B have been aggregated in this table as Section A members have typically elected to take Section B benefits at retirement.

Summary of Fair Value of Assets of BTPS Analysed by Asset Category

The fair value of the assets of the BTPS analysed by asset category are shown below. These are subdivided by assets that have a quoted market price in an active market and those that do not (such as investment funds).

		2018a									2017a
		Total assets £bn			of which quoted     £bn		b	Total %			Total assets £bn			of which quoted £bn		b	Total %
Growth
Equities	UK		0.5			0.5			1			0.7			0.6			2
	Overseas developed		7.8			7.3			16			9.1			8.6			18
	Emerging markets		0.5			0.4			1			0.5			0.1			1
Private Equity			1.9			–			4			1.9			–			4
Property	UK		3.9			–			8			4.1			–			8
	Overseas		1.2			–			2			1.7			–			3
Other growth assets	Absolute Return fundsc		1.5			–			3			2.3			–			5
	Non Core Creditd		3.4			1.0			7			3.5			1.1			7
	Mature Infrastructure		1.4			–			3			1.7			–			3
Liability matching
Government bonds	UK Index Linked		12.5			12.5			25			12.3			12.0			25
Investment grade credit	Global		10.0			8.0			20			7.6			5.9			15
Cash, derivatives and other
Cash balances			3.8			–			7			1.7			–			3
Longevity insurance contracte			(0.4	)		–			(1	)		(0.3	)		–			(1	)
Other non-physical cashf			1.9			–			4			3.3			–			7
Total			49.9			29.7			100			50.1			28.3			100

^a At 31 March 2018, the Scheme’s assets included equity issued by the group of £3m (2016/17: £nil) . The Scheme also held £10m (2016/17: £10m) of index-linked bonds issued by the group.

^bAssets with a quoted price in an active market.

^cThis allocation seeks to generate returns irrespective of the direction of markets. Managers within this allocation will typically manage their portfoilios without close regard to a specific market benchmark.

^dThis allocation includes a range of credit investments, including emerging market, sub-investment grade and unrated credit. The allocation seeks to exploit investment opportunities within credit markets using the expertise of a range of specialist investment managers.

^eThe Trustee has hedged some of the Scheme’s longevity risk through a longevity insurance contract which was entered into in 2014. The value reflects experience to date on the contract from higher than expected deaths. This amount partly offsets a reduction recognised in the Scheme’s liabilities.

^f Non-physical cash includes offsets in future positions and cash collateral posted in relation to derivatives held by the Scheme.

Summary of Approach Used to Set Key IAS 19 Assumptions

The table below summarises the approach used to set the key IAS 19 assumptions for the BTPS.

	Approachtosetthe assumption
Discountrate	IAS 19 requires that the discount rate is determined by reference to market yields at the reporting date on high quality corporate bonds. The currency and term of these should be consistent with the currency and estimated term of the pension obligations. The assumption is calculated by applying the projected BTPS benefit cash flows to a corporate bond yield curve constructed based on the yield on AA-rated corporate bonds. In setting the yield curve, judgement is required on the selection of appropriate bonds to be included in the universe and the approach used to then derive the yield curve. At 31 March 2018, the discount rate model used to select bonds and derive the yield curve was updated to better reflect yields on corporate bonds over the life of the Scheme. A key difference is that the revised model excludes bonds which have either an implicit or explicit Government guarantee, which is more consistent with the requirements of IAS19, and reflects developing practice. Both the old and revised models are standard models developed by our external actuary. The impact of this change is a £2.1bn reduction in the BTPS liabilities.
RPIinflation	The RPI inflation assumption is set using the entire inflation curve, weighted by projected BTPS benefit cash flows, and making an adjustment for an inflation risk premium (to reflect the extra premium paid by investors for inflation protection), which is currently assumed to be 20bps.
CPIinflation	CPIisassessedata marginbelowRPItakingintoaccountmarketforecastsandindependentestimatesoftheexpected difference.
Salaryincreases	Long-termsalaryincreasesforBTPSmembersareassumedtobeequaltoCPIinflation.
Pensionincreases	Benefitsareassumedtoincreasein linewiththeRPIorCPIinflationassumptions,basedontherelevantindexfor increasingbenefits,asprescribedbytherulesoftheBTPSandsummarisedabove.
Longevity	The longevity assumption has been updated to take into account: –  the actual mortality experience of the BTPS pensioners, based on a formal review conducted at the 2014 triennial funding valuation –  future improvements in longevity based on a model published by UK actuarial profession’s Continuous Mortality Investigation (using the CMI 2016 Mortality Projections model with a 1.25% per year long-term improvement parameter).

Summary of Key Financial Assumptions Used to Measure Liabilities of BTPS

Thekey financial assumptionsused tomeasure theliabilitiesof the BTPSare shown below.

	Nominal rates (per year)									Real rates (per year)a
At 31 March	2018 %			2017 %			2016 %			2018 %			2017 %			2016 %
Rate used to discount liabilities		2.65			2.40			3.30			(0.44)			(0.78)			0.44
Inflation – increase in RPI		3.10			3.20			2.85		–				–			–
Inflation – increase in CPI	2.00		b	2.00		c	1.65		d	(1.1)		b	(1.2)		c	(1.2)		d

^aThe real rate is calculated relative to RPI inflation.

^bAssumed to be 0.1% higher until 31 March 2023.

^cAssumed to be 0.5% higher until 31 March 2019.

^dAssumed to be 0.2% higher until 31 March 2017.

Summary of Average Life Expectancies for Members Aged Sixty

Theaverage lifeexpectancyassumptions atthevaluation dates,formembers60 yearsof age,are asfollows.

Number of years from valuation date	June 2017 assumptions	June 2014 assumptions
Male in lower pay bracket	25.9	26.1
Male in medium pay bracket	27.2	27.5
Male in high pay bracket	28.6	29.0
Female in lower pay bracket	28.6	28.9
Female in high pay bracket	28.9	29.2
Average improvement for a member retiring at age 60 in 10 years’ time	0.9	1.3

Summary of Assessed Potential Negative Impact of Key Risk

BT’sindependent actuaryhas assessed thepotential negative impactof thekeyrisksthatmight occurno more than once in every 20 years illustrated as the following three scenarios:

Scenario	1-in-20 events
	2018		2017
1. Fall in discount ratea		1.10%		1.00%
2. Increase to inflation rateb		0.70%		0.90%
3. Increase to life expectancy		1.35 years		1.35 years

^aScenario assumes a fall in the yields on both government and corporate bonds.

^bAssuming RPI, CPI, pension increases and salary increases all increase by the same amount.

Summary of Two Most Recent Triennial Valuations

Theresults of the two mostrecenttriennial valuations are shown below.

	June 2017 valuation £bn	June 2014 valuation £bn
BTPS liabilities	(60.4)		(47.2	)
Market value of BTPS assets	49.1	40.2
Funding deficit	(11.3)		(7.0	)
Percentage of accrued benefits covered by BTPS assets at the valuation date	81.3%	85.2%
Percentage of accrued benefits on a solvency basis covered by the BTPS assets at the valuation date	62.2%	63.0%

Summary of Prudent Long-Term Assumptions

Thesevaluations were determinedusing thefollowingprudentlong-term assumptions.

	Nominal rates (per year)		Real rates (per year)a
	June 2017 valuation %	June 2014 valuation %	June 2017 valuation %	June 2014 valuation %
Average single equivalent discount rate	2.6	4.5	(0.8)		1.0
Average long-term increase in RPI	3.4	3.5	–	–
Average long-term increase in CPI	2.4	2.5	(1.0)		(1.0	)

a Therealrateiscalculatedrelativeto RPIinflationandisshownasa comparator.

Summary of Payments Made to BTPS

Payments made to the BTPS

Year ended 31 March	2018 £m		2017 £m
Ordinary contributions		248	303
Deficit contributions		850	250
Total contributions in the year		1,098		553

Schedule of Future Deficit Payment to BTPS

BTis scheduled tomake future deficit payments to the BTPSin line withthetable below.

Year to 31 March	2018	2019		2020		2021		2022		2023	2024	2025	2026	2027	2028	2029	2030
Deficit contribution (£m)	850	2,000	a	1,250	b	900	c	900	d	907	907	907	907	907	907	907	907

^a due to be paid shortly, but no later than 30 June 2019.

^bpayable by 30 June 2019.

^c£400m payable by 30 June 2020.

^d£200m payable by 30 June 2021.

BTPS [Member]

Disclosure Of Defined Benefit Plans [Line Items]

Summary of Average Life Expectancies for Members Aged Sixty

Basedon the IAS19 longevity assumptions,theforecast life expectanciesfor BTPSmembersaged 60 are as follows:

At 31 March	2018 Number of years		2017 Number of years
Male in lower pay bracket		25.8		26.2
Male in medium pay bracket		27.1		27.5
Male in higher pay bracket		28.5		28.9
Female in lower pay bracket		28.5		28.9
Female in higher pay bracket		28.7		29.2
Average improvement for a member retiring at age 60 in 10 years' time		0.7		1.0

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Share-based payments (Tables)

12 Months Ended

Mar. 31, 2018

Text Block1 [Abstract]

Summary of Plans and Analysis of Total Charge by Type of Award

Year ended 31 March	2018 £m	2017 £m	2016 £m
Employee Saveshare Plans	42	40	27
Executive Share Plans:
Incentive Share Plan (ISP)	16	–	21
Deferred Bonus Plan (DBP)	4	9	4
Retention Share Plan (RSP)a	21	8	1
Other plans	1	–	5
	84	57	58

^a Re-presented to show RSPs separately from other plans.

Movements in Employee Saveshare Options

Movements in Employee Saveshare options are shown below.

	Movement in the number of share options									Weighted average exercise price
Year ended 31 March	2018 millions			2017 millions			2016 millions			2018 pence		2017 pence	2016 pence
Outstanding at 1 April		189		197			226				313	287	226
Granted		69		44			47				250	362	385
Forfeited		(41	)		(18	)		(12	)		328	345	306
Exercised		(30	)		(33	)		(63	)		169	208	139
Expired		(12	)		(1	)		(1	)		353	345	247
Outstanding at 31 March		175		189			197				306	313	287
Exercisable at 31 March	–			–			–				320	237	140

Summarises Information Relating to Options Outstanding and Exercisable Under Employee Saveshare Plans

The following table summarises information relating to options outstanding and exercisable under Employee Saveshare plans at 31 March 2018.

Normal dates of vesting and exercise (based on calendar years)	Exercise price per share	Weighted average exercise price			Number of outstanding options millions		Weighted average remaining contractual life
2018	249p – 423p		306	p		25	10 months
2019	319p – 397p		333	p		53	22 months
2020	243p – 376p		307	p		44	34 months
2021	353p		353	p		17	46 months
2022	243p		243	p		36	58 months
Total			306	p		175	33 months

Movements in Executive Share Plan Awards

Movements in executive share plan awards during 2017/18 are shown below:

	Number of shares (millions)
	ISP			DBP			RSP			Total
At 1 April 2017		45			7			4			56
Awards granted		26			2			10			38
Awards vested		–			(3	)		(2	)		(5	)
Awards lapsed		(20	)		–			(1	)		(21	)
Dividend shares reinvested		3			–			1			4
At 31 March 2018		54			6			12			72

Summary of Fair Values and Key Assumptions Used for Valuing Grants Made Under Employee Saveshare Plans and ISP

The following table summarises the fair values and key assumptions used for valuing grants made under the Employee Saveshare plans and ISP in 2017/18, 2016/17 and 2015/16.

			2018			2017		2016
Year ended 31 March	Employee Saveshare		ISP		Employee Saveshare	ISP	Employee Saveshare	ISP
Weighted average fair value		56p		202p	72p	328p	81p	364p
Weighted average share price		296p		281p	422p	426p	454p	451p
Weighted average exercise price		250p	n/a		362p	n/a	385p	n/a
Expected dividend yield	3.12% – 3.21%		n/a		2.9% – 3.4%	n/a	3.2% –3.7%	n/a
Risk free rates	0.1% – 0.2%			0.2%	0.5% – 0.8%	0.6%	0.7% – 1.6%	0.7%
Expected volatility	23.1% – 24.3%			23.6%	19.0% – 21.5%	21.8%	19.7% –22.7%	22.0%

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Investments (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Investments [Abstract]

Summary of Investments

At 31 March	2018 £m		2017 £m		2016 £m
Non-current assets
Available-for-sale		46		37		39
Amounts owed by ultimate parent company		2,983		1,371		1,409
Amounts owed by parent company		10,318		10,191		10,510
Fair value through profit or loss		7		7		7
		13,354		11,606		11,965
Current assets
Available-for-sale		2,575		1,437		2,878
Amounts owed by ultimate parent company		34		28		26
Amounts owed by parent company		168		192		327
Loans and receivables		447		83		40
		3,224		1,740		3,271

Fair Value Hierarchy of Investments

Fair value hierarchy At 31 March 2018	Level 1 £m		Level 2 £m		Level 3 £m		Total held at fair value £m
Non-current and current investments
Available-for-sale investments		32		2,575		14		2,621
Fair value through profit or loss		7	–		–			7
Total		39		2,575		14		2,628

At 31 March 2017	Level 1 £m		Level 2 £m		Level 3 £m		Total held at fair value £m
Non-current and current investments
Available-for-sale investments		21		1,437		16		1,474
Fair value through profit or loss		7		–		–		7
Total		28		1,437		16		1,481

At 31 March 2016	Level 1 £m		Level 2 £m		Level 3 £m		Total held at fair value £m
Non-current and current investments
Available-for-sale investments		24	2,878		15		2,917
Fair value through profit or loss		7		–		–		7
Total		31		2,878		15		2,924

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Cash and cash equivalents (Tables)

12 Months Ended

Mar. 31, 2018

Cash And Cash Equivalents [Abstract]

Summary of Cash and Cash Equivalents

At 31 March	2018 £m			2017 £m			2016 £m
Cash at bank and in hand		439			467			893
Cash equivalents
Loans and receivables
US deposits		26			32			44
UK deposits		31			1			20
Other deposits		25			26			32
Total cash equivalents		82			59			96
Total cash and cash equivalents		521			526			989
Bank overdrafts (note 23)		(29	)		(17	)		(537	)
Cash and cash equivalents per the cash flow statement		492			509			452

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Loans and other borrowings (Tables)

12 Months Ended

Mar. 31, 2018

Text Block1 [Abstract]

Summary of Key Components of External Gross Debt

The table below shows the key components of external gross debt and of the increase of £2,195m this year.

	At 1  April 2017 £m			Issuance/ (maturities) £m			Fair value movements £m			Foreign exchange £m			Transfer to within one year £m			Accrued interest movements £m		At 31 March 2018 £m
Debt due within one yeara		2,632			(1,401	)		(18	)		(95	)		1,163		–			2,281
Debt due after one year		10,081			3,760			(60	)		(440	)		(1,347	)	–			11,994
Cash flows from Derivatives related to net debt	–				(188	)	–			–				188		–		–
Overdrafts	–				4		–			–				(4	)	–		–
Impact of cross-currency swapsb		(1,419	)	–			–				545		–			–			(874	)
Removal of the accrued interest and fair value adjustmentsc		(314	)	–				78		–			–				10		(226	)
External gross debt		10,980			2,175		–				10		–				10		13,175

^aIncluding accrued interest and bank overdrafts.

^bTranslation of debt balances at swap rates where hedged by cross currency swaps.

^cRemoval of accrued interest applied to reflect the effective interest rate method and removal of fair value adjustments.

Summary of Reconciliation From Most Directly Comparable IFRS Measure to Net Debt

The table below gives the details of the listed bonds and other debt.

At 31 March	2018 £m		2017 £m		2016 £m
1.625% US$600m bond due June 2016a		–		–		419
8.50% £678m bond due December 2016 (minimum 7.50%b)		–		–		696
3.5% €500m bond due February 2017a		–		–		398
1.25% US$500m bond due February 2017a		–		–		348
6.625% £500m bond due June 2017a		–		526		525
5.95% US$1,100m bond due January 2018a		–		891		775
3.25% €600m bond due August 2018a		541		539		510
2.35% US$800m bond due February 2019a		572		642		558
4.38% £450m bond due March 2019		455		460		464
1.125% €1,000m bond due June 2019a		883		863		800
8.625% £300m bond due March 2020		300		300		300
0.625% €1,500m bond due March 2021a		1,309		1,282		1,190
0.5% €575m bond due June 2022a		502		–		–
1.125% €1,100m bond due March 2023a		961		942		873
1% €575m bond due June 2024a		506		–		–
1% €1,100m bond due November 2024a		959		–		–
3.50% £250m index linked bond due April 2025		419		403		396
1.75% €1,300m bond due March 2026a		1,137		1,113		1,032
1.5% €1,150m bond due June 2027a		1,009		–		–
5.75% £600m bond due December 2028		721		731		741
9.125% US$2,670m bond due December 2030a (minimum 8.625%b)		1,943		2,191		1,910
3.125% £500m bond due November 2031		502		–		–
6.375% £500m bond due June 2037a		522		522		522
3.625% £250m bond due November 2047		250		–		–
Total listed bonds		13,491		11,405		12,457
Finance leases		223		229		233
LIBOR + 0.95% £438m Syndicated loan facilities due April 2016	–		–			438
2.21% £350m bank loan due December 2017	–			352		354
Acquisition facility	–		–			181
Other loans		532		710		561
Bank overdrafts (note 22)		29		17		537
Amounts due to ultimate companyc		1,061		1,183		1,024
Total other loans and borrowings		1,622		2,262		3,095
Total loans and borrowings		15,336		13,896		15,785

^aDesignated in a cash flow hedge relationship.

^bThe interest rate payable on this bond attracts an additional 0.25% for a downgrade by one credit rating by either Moody’s or S&P to the group’s senior unsecured debt below A3/A–respectively. In addition, if Moody’s or S&P subsequently increase the ratings then the interest rate will be decreased by 0.25% for each rating category upgrade by each rating agency. In no event will the interest rate be reduced below the minimum rate reflected in the above table.

^cAmounts due to ultimate parent company are denominated in Sterling and incur a floating rate of interest based on LIBOR.

Summary of Loans and Other Borrowings

Loans and otherborrowings are analysed asfollows:

At 31 March	2018 £m		2017 £m		2016 £m
Current liabilities
Listed bonds		1,702		1,539		2,013
Finance leases		18		15		8
Bank loans	–			352		–
Syndicated loan facilities	–			–		619
Other loans and bank overdraftsa		561		726		1,096
Amounts due to ultimate parent company		17		159		20
Total current liabilities		2,298		2,791		3,756
Non-current liabilities
Listed bonds		11,789		9,866		10,444
Finance leases		205		214		225
Bank loans	–		–			354
Other loans	–			1		2
Amounts due to ultimate parent company		1,044		1,024		1,004
Total non-current liabilities		13,038		11,105		12,029
Total		15,336		13,896		15,785

^aIncludescollateralreceivedon swapsof £525m(2016/17:£702m,2015/16:£553m).

Summary of Principal Repayments of Loans and Other Borrowings

The principal repaymentsofloans and borrowingsat hedgedrates amountedto£14,219m(2016/17:£12,138m,2015/16: £14,756m)and repayments fall due asfollows:

	2018							2017							2016
At 31 March	Carrying amount £m		Effect of hedging and interest £m			Principal repayments at hedged rates £m		Carrying amount £m		Effect of hedging and interest £m			Principal repayments at hedged rates £m		Carrying amount £m		Effect of hedging and interest £m			Principal repayments at hedged rates £m
Within one year, or on demand		2,289		(308	)		1,981		2,791		(523	)		2,268		3,756		(252	)		3,504
Between one and two years		1,192		(66	)		1,126		1,614		(197	)		1,417		1,632		(216	)		1,416
Between two and three years		1,332		(154	)		1,178		1,166		(43	)		1,123		1,488		(72	)		1,416
Between three and four years		18	–				18		1,295		(121	)		1,174		1,103		18			1,121
Between four and five years		1,489		(111	)		1,378		12		–			12		1,199		(26	)		1,173
After five years		8,943		(405	)		8,538		6,868		(724	)		6,144		6,428		(302	)		6,126
Total due for repayment after more than one year		12,974		(736	)		12,238		10,955		(1,085	)		9,870		11,850		(598	)		11,252
Total repayments		15,263		(1,044	)		14,219		13,746		(1,608	)		12,138		15,606		(850	)		14,756
Fair value adjustments		73							150							179
Total loans and other borrowings		15,336							13,896							15,785

Summary of Obligations Under Finance Leases

Obligationsunder finance leases are analysed asfollows:

	2018			2017			2016			2018		2017		2016
	Minimum lease payments									Repayment of outstanding lease obligations
At 31 March				£m			£m					£m		£m
Amounts payable under finance leases:
Due within one year		33			29			13			18		14		8
Between two to five years		122			102			105			71		50		51
After five years		193			237			265			130		165		174
		348			368			383			219		229		233
Less: future finance charges		(129	)		(139	)		(150	)	–		–		–
Fair value adjustments for purchase price adjustment		4		–			–				4	–		–
Total finance lease obligations		223			229			233			223		229		233

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Finance expense (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Finance Income Expense [Abstract]

Summary of Finance Expense and Income

Year ended 31 March	2018 £m		2017 £m			2016 £m
Finance expense
Interest on:
Financial liabilities at amortised cost and associated derivatives		478		567			489
Finance leases		16		15			14
Derivatives		14		12			11
Fair value movements on derivatives not in a designated hedge relationship		1		(2	)		(5	)
Reclassification of cash flow hedge from other comprehensive income		34		(1	)		3
Unwinding of discount on provisions		15		16			8
Interest payable on ultimate parent company borrowings		18		25			20
Total finance expense before specific items		576		632			540
Specific items (note 8)		218		210			229
Total finance expense		794		842			769

Year ended 31 March	2018 £m		2017 £m		2016 £m
Finance income
Interest on available-for-sale investments		5		6		8
Interest on loans and receivables		7		7		6
Other interest and similar income	–		–			23
Interest income on loans to immediate and ultimate parent company		203		219		352
Total finance income		215		232		389
Year ended 31 March	2018 £m		2017 £m		2016 £m
Net finance expense before specific items		361		400		151
Specific items (note 8)		218		210		229
Net finance expense		579		610		380

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Financial instruments and risk management (Tables)

12 Months Ended

Mar. 31, 2018

Text Block1 [Abstract]

Summary of Currency and Interest Rate Profile of Loans and Borrowings

The table below reflects the currency and interest rate profile of our loans and borrowings after the impact of hedging.

	2018						2017						2016
At 31 March	Fixed rate interest £m		Floating rate interest £m		Total £m		Fixed rate interest £m		Floating rate interest £m		Total £m		Fixed rate interest £m		Floating rate interest £m		Total £m
Sterling		11,990		1,720		13,710		9,633		1,864		11,497		11,417		2,752		14,169
Euro	–			509		509	–			641		641	–			587		587
Total		11,990		2,229		14,219		9,633		2,505		12,138		11,417		3,339		14,756
Ratio of fixed to floating		84%		16%	100%			79%		21%	100%			77%		23%	100%
Weighted average effective
fixed interest rate – Sterling	4.4%						4.9%						6.0%

Summary of Impact on Equity, Before Tax, of a 1% Increase in Interest

The impact on equity, before tax, of a 1% increase in interest rates and a 10% strengthening in Sterling against other currencies is as detailed below:

At 31 March	2018 £m Increase (reduce)			2017 £m Increase (reduce)			2016 £m Increase (reduce)
Sterling interest rates		628			554			626
US Dollar interest rates		(267	)		(348	)		(374	)
Euro interest rates		(401	)		(229	)		(263	)
Sterling strengthening		(236	)		(269	)		(98	)

Summary of Credit Ratings

Our credit ratings were as detailed below:

	2018		2017		2016
At 31 March	Rating	Outlook	Rating	Outlook	Rating	Outlook
Rating agency
Moody’s	Baa2	Stable	Baa1	Negative	Baa2	Positive
Standard & Poor’s	BBB+	Negative	BBB+	Negative	BBB	Positive

Remaining Contractually-Agreed Cash Flows Including Interest Payable for Non-Derivative Financial Liabilities on Undiscounted Basis

The following table provides an analysis of the remaining contractually-agreed cash flows including interest payable for our non- derivative financial liabilities on an undiscounted basis, which therefore differs from both the carrying value and fair value.

Non-derivative financial liabilities At 31 March 2018	Loans and other borrowings £m		Interest on loans and other borrowings £m			Trade and other payables £m		Provisions £m			Total £m
Due within one year		2,120		468			4,961		54			7,603
Between one and two years		1,192		421		–			34			1,647
Between two and three years		1,332		381		–			25			1,738
Between three and four years		18		374		–			43			435
Between four and five years		1,489		372		–			19			1,880
After five years		8,943		3,300		–			197			12,440
		15,094		5,316			4,961		372			25,743
Interest payments not yet accrued	–			(5,147	)	–		–				(5,147	)
Fair value adjustment		73	–			–		–				73
Impact of discounting	–		–			–			(72	)		(72	)
Carrying value on the balance sheeta		15,167		169			4,961		300			20,597

^a Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Non-derivative financial liabilities At 31 March 2017	Loans and other borrowings £m		Interest on loans and other borrowings £m			Trade and other payables £m		Provisions £m			Total £m
Due within one year		2,602		532			5,298		62			8,494
Between one and two years		1,614		415			–		41			2,070
Between two and three years		1,166		364			–		21			1,551
Between three and four years		1,295		327			–		18			1,640
Between four and five years		12		319			–		17			348
After five years		6,868		2,726			–		310			9,904
		13,557		4,683			5,298		469			24,007
Interest payments not yet accrued		–		(4,494	)		–		–			(4,494	)
Fair value adjustment		150		–			–		–			150
Impact of discounting		–		–			–		(177	)		(177	)
Carrying value on the balance sheeta		13,707		189			5,298		292			19,486

^a Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Non-derivative financial liabilities At 31 March 2016	Loans and other borrowings £m		Interest on loans and other borrowings £m			Trade and other payables £m		Provisions £m			Total £m
Due within one year		3,558		513			5,346		50			9,467
Between one and two years		1,632		435			–		30			2,097
Between two and three years		1,488		357			–		25			1,870
Between three and four years		1,103		343			–		15			1,461
Between four and five years		1,199		308			–		16			1,523
After five years		6,428		2,885			–		326			9,639
		15,408		4,841			5,346		462			26,057
Interest payments not yet accrued		–		(4,643	)		–		–			(4,643	)
Fair value adjustment		179		–			–		–			179
Impact of discounting		–		–			–		(166	)		(166	)
Carrying value on the balance sheeta		15,587		198			5,346		296			21,427

^a Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Disclosure Of Maturity Analysis For Derivative Financial Liabilities Explanatory

The following table provides an analysis of the contractually agreed cash flows in respect of the group’s derivative financial instruments. Cash flows are presented on a net or gross basis in accordance with the settlement arrangements of the instruments.

	Derivatives – Analysed by earliest payment datea									Derivatives – Analysed based on holding instrument to maturity
Derivative financial liabilities At 31 March 2018	Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m		Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m
Due within one year		140		587		(547	)		180		91		587		(547	)		131
Between one and two years		135		183		(166	)		152		91		183		(166	)		108
Between two and three years		156		442		(446	)		152		85		69		(47	)		107
Between three and four years		143		52		(29	)		166		80		68		(47	)		101
Between four and five years		161		52		(29	)		184		80		68		(47	)		101
After five years		291		2,234		(2,149	)		376		599		2,575		(2,512	)		662
Totalb		1,026		3,550		(3,366	)		1,210		1,026		3,550		(3,366	)		1,210

^b Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

	Derivatives – Analysed by earliest payment datea									Derivatives – Analysed based on holding instrument to maturity
Derivative financial liabilities At 31 March 2017	Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m		Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m
Due within one year		291		582		(576	)		297		92		582		(576	)		98
Between one and two years		296		1,139		(1,097	)		338		92		1,139		(1,097	)		134
Between two and three years		198		–		–			198		92		–		–			92
Between three and four years		114		–		–			114		88		–		–			88
Between four and five years		104		–		–			104		83		–		–			83
After five years		123		–		–			123		679		–		–			679
Totalb		1,126		1,721		(1,673	)		1,174		1,126		1,721		(1,673	)		1,174

	Derivatives – Analysed by earliest payment datea										Derivatives – Analysed based on holding instrument to maturity
Derivative financial liabilities At 31 March 2016	Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m			Net settled £m		Gross settled outflows £m		Gross settled inflows £m			Total £m
Due within one year		268		263		(250	)		281			91		263		(250	)		104
Between one and two years		386		38		(27	)		397			88		38		(27	)		99
Between two and three years		371		38		(27	)		382			88		38		(27	)		99
Between three and four years		60		838		(836	)		62			90		838		(836	)		92
Between four and five years		81		17		(18	)		80			84		17		(18	)		83
After five years		–		165		(180	)		(15	)		725		165		(180	)		710
Totalb		1,166		1,359		(1,338	)		1,187			1,166		1,359		(1,338	)		1,187

^aCertain derivative financial instruments contain break clauses whereby either the group or bank counterparty can terminate the swap on certain dates and the mark to market position is settled in cash.

^b Foreign currency-related cash flows were translated at closing rates as at the relevant reporting date. Future variable interest rate cash flows were calculated using the most recent rate applied at the relevant balance sheet date.

Summary of Maximum Credit Risk Exposure of Financial Assets

The maximum credit risk exposure of the group’s financial assets at the balance sheet date is as follows:

At 31 March	Notes		2018 £m		2017 £m		2016 £m
Derivative financial assets				1,509		2,246		1,639
Investments		21		16,578		13,346		15,236
Trade and other receivablesc		16		2,533		2,754		2,884
Cash and cash equivalents		22		521		526		989
				21,141		18,872		20,748

^cThe carrying amount excludes £317m (2016/17: £360m, 2015/16: £218m) of non-current trade and other receivables which relate to non-financial assets, and £1,496m (2016/17: £1,106m, 2015/16: £1,103m) of prepayments and other receivables.

Summary of Credit Quality and Credit Concentration of Cash Equivalents, Current Asset Investments and Derivative Financial Assets

The credit quality and credit concentration of cash equivalents, current asset investments and derivative financial assets are detailed in the tables below. Where the opinion of Moody’s and S&P differ, the lower rating is used.

Moody’s/S&P credit rating of counterparty	2018 £m		2017 £m		2016 £m
Aa2/AA and above		2,575		1,444		2,878
Aa3/AA–		313		208		120
A1/A+a		651		952		64
A2/Aa		628		370		939
A3/A–a		180		204		160
Baa1/BBB+a		59		561		492
Baa2/BBB and belowa		207		86		–
		4,613		3,825		4,653

^aWe hold cash collateral of £492m (2016/17: £702m, 2015/16: £553m) in respect of derivative financial assets with certain counterparties.

Summary of Offsetting of Financial Assets and Liabilities

The table below shows our financial assets and liabilities that are subject to offset in the group’s balance sheet and the impact of enforceable master netting or similar agreements.

				Related amounts not set off in the balance sheet
Financial assets and liabilities At 31 March 2018	Amounts presented in the balance sheet £m			Right of set off with derivative counterparties £m			Cash collateral £m			Net amount £m
Derivative financial assets		1,509			(754	)		(492	)		263
Derivative financial liabilities		(837	)		754			60			(23	)
Total		672			–			(432	)		240

				Related amounts not set off in the balance sheet
Financial assets and liabilities At 31 March 2017	Amounts presented in the balance sheet £m			Right of set off with derivative counterparties £m			Cash collateral £m			Net amount £m
Derivative financial assets		2,246			(693	)		(702	)		851
Derivative financial liabilities		(903	)		693			64			(146	)
Total		1,343			–			(638	)		705

				Related amounts not set off in the balance sheet
Financial assets and liabilities At 31 March 2016	Amounts presented in the balance sheet £m			Right of set off with derivative counterparties £m			Cash collateral £m			Net amount £m
Derivative financial assets		1,639			(456	)		(553	)		630
Derivative financial liabilities		(911	)		456			40			(415	)
Total		728			–			(513	)		215

Summary of Derivative Financial Instruments are Held at Fair Value on Balance Sheet

All of our derivative financial instruments are held at fair value on the balance sheet. The fair values of outstanding swaps and foreign exchange contracts are estimated using discounted cash flow models and market rates of interest and foreign exchange at the balance sheet date.

At 31 March 2018	Current asset £m		Non-current asset £m		Current liability £m		Non-current liability £m
Designated in a cash flow hedge		187		1,061		41		587
Other		10		251		9		200
Total derivatives		197		1,312		50		787

At 31 March 2017	Current asset £m		Non-current asset £m		Current liability £m		Non-current liability £m
Designated in a cash flow hedge		417		1,508		25		616
Other		11		310		9		253
Total derivatives		428		1,818		34		869

At 31 March 2016	Current asset £m		Non-current asset £m		Current liability £m		Non-current liability £m
Designated in a cash flow hedge		166		1,158		40		618
Other		11		304		8		245
Total derivatives		177		1,462		48		863

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Other reserves (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Reserves Within Equity [Abstract]

Summary of Other Reserves

	Other comprehensive income
	Cash flow reserve £m		a	Available- for-sale reserve £m		b	Translation reserve £m		c	Merger and other reserves £m		d	Total £m
At 1 April 2015		55			18			278			858			1,209
Exchange differences		–			–			29			–			29
Net fair value gain on cash flow hedges		381			–			–			–			381
Recognised in income and expense		(230	)		–			–			–			(230	)
Fair value movement on available-for-sale assets		–			(2	)		–			–			(2	)
Tax recognised in other comprehensive income		(33	)		–			38			–			5
At 1 April 2016		173			16			345			858			1,392
Exchange differences		–			–			227			–			227
Net fair value gain on cash flow hedges		884			–			–			–			884
Recognised in income and expense		(938	)		–			–			–			(938	)
Fair value movement on available-for-sale assets		–			(3	)		–			–			(3	)
Tax recognised in other comprehensive income		8			–			21			–			29
At 31 March 2017		127			13			593			858			1,591
Exchange differencese		–			–			(188	)		–			(188	)
Net fair value loss on cash flow hedges		(368	)		–			–			–			(368	)
Recognised in income and expense		277			–			–			–			277
Fair value movement on available-for-sale assets		–			11			–			–			11
Tax recognised in other comprehensive income		10			–			(9	)		–			1
Transfer to realised profit		(83	)		–			–			–			(83	)
At 31 March 2018		(37	)		24			396			858			1,241

^a The cash flow reserve is used to record the effective portion of the cumulative net change in the fair value of cash flow hedging instruments related to hedged transactions that have not yet occurred. Amounts ‘recognised in income and expense’ include a net credit to the cash flow reserve of £295m (2016/17: charge of £941m, 2015/16: charge of £255m) relating to fair value movements on derivatives. The items generating these foreign exchange movements are in designated cash flow hedge relationships.

^b The available-for-sale reserve is used to record the cumulative fair value gains and losses on available-for-sale financial assets. The cumulative gains and losses are recycled to the income statement on disposal of the assets.

^c The translation reserve is used to record cumulative translation differences on the assets and liabilities of foreign operations. The cumulative translation differences are recycled to the income statement on disposal of the foreign operation.

^d Excludes £1m (2016/17: £10m, 2015/16: £nil) of exchange differences in relation to retained earnings attributed to non-controlling interests.

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Related Party Transactions (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Transactions Between Related Parties [Abstract]

Balances with Parent and Ultimate Parent Companies and Finance Income or Expense

A summary of the balances with the parent and ultimate parent companies and the finance income or expense arising in respect of these balances is set out below:

			2018						2017						2016
	Notes		Asset (liability) at 31 March £m			Finance income (expense) £m			Asset (liability) at 31 March £m			Finance income (expense) £m			Asset (liability) at 31 March £m			Finance income (expense) £m
Amounts owed by (to) parent company
Loan facility – non-current assets investments	21,24			10,318			169			10,191			191			10,510			326
Loan facility  – current asset investments		21		168		n/a				192		n/a				327		n/a
Trade and other payables		17		(50	)	n/a				(63	)	n/a				(70	)	n/a
Amounts owed by (to) ultimate parent companya
Non-current assets investments	21,24			2,983			34			1,371			28			1,409			26
Non-current liabilities loans		23		(1,044	)		(18	)		(1,024	)		(25	)		(1,004	)		(20	)
Trade and other receivables		16		15		n/a				25		n/a				9		n/a
Current asset investments		21		34		n/a				28		n/a				26		n/a
Current liabilities loans		23		(18	)	–				(159	)	–				(20	)	–

^aDuring the year we made cash payments of £1,722m to BT Group plc offset by the receipt of £45m from BT Group plc resulting in net cash outflow of £1,677m. In addition there are non cash movements of £63m on non-current asset investments relating to interest on loans, employee share schemes and tax settlements made by BT plc on behalf of BT Group plc.

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Financial commitments and contingent liabilities (Tables)

12 Months Ended

Mar. 31, 2018

Financial Commitments [Abstract]

Disclosure of Financial Commitments

Financial commitments were as follows:

At 31 March	2018 £m		2017 £m
Capital commitments		993		889
Other commitments		362		367
Device purchase commitments		262		423
TV programme rights commitments		2,823		2,644
Total		4,440		4,323

Disclosure of Future Minimum Operating Lease Payments

Future minimum operating lease payments were as follows:

	2018 £m		2017 £m
Payable in the year ending 31 March:
2018		–		650
2019		600		610
2020		550		558
2021		513		532
2022		486		505
2023		463		475
Thereafter		3,985		3,830
Total future minimum operating lease payments		6,597		7,160

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Post Balance Sheet Events (Tables)

12 Months Ended

Mar. 31, 2018

Disclosure Of Nonadjusting Events After Reporting Period [Line Items]

Summary of Results of Reportable Segments

We have set out below information regarding the results of each reportable segment.

Segment revenueandprofit

Year ended 31 March 2018	BT Consumer £m			EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		5,066			5,294			4,563			5,013			2,009			5,123			8			27,076
Internal revenue		(66	)		(37	)		(115	)		–			(134	)		(2,978	)		–			(3,330	)
Revenue from external customersa		5,000			5,257			4,448			5,013			1,875			2,145			8			23,746
EBITDAb		1,023			1,353			1,418			434			754			2,520			6			7,508
Depreciation and amortisation		(216	)		(776	)		(365	)		(424	)		(311	)		(1,360	)		(62	)		(3,514	)
Operating profit (loss)a		807			577			1,053			10			443			1,160			(56	)		3,994
Specific items (note 8)																							(610	)
Operating profit																							3,384
Net finance expensec																							(579	)
Share of post tax profit (loss) of associates and joint ventures																							(1	)
Profit before tax																							2,804

Year ended 31 March 2017	BT Consumer £m			EE £m			Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		4,934			5,090			4,758			5,479			2,109			5,098			10			27,478
Internal revenue		(63	)		(37	)		(122	)		–			(138	)		(3,036	)		–			(3,396	)
Revenue from external customersa		4,871			5,053			4,636			5,479			1,971			2,062			10			24,082
EBITDAb		1,012			1,156			1,528			495			834			2,633			(10	)		7,648
Depreciation and amortisation		(209	)		(780	)		(352	)		(439	)		(306	)		(1,369	)		(55	)		(3,510	)
Operating profit (loss)a		803			376			1,176			56			528			1,264			(65	)		4,138
Specific items (note 8)																							(968	)
Operating profit																							3,170
Net finance expensec																							(610	)
Share of post tax profit (loss) of associates and joint ventures																							(9	)
Profit before tax																							2,551

Year ended 31 March 2016	BT Consumer £m			EE £m		d	Business and Public Sector £m			Global Services £m			Wholesale and Ventures £m			Openreach £m			Other £m			Total £m
Segment revenue		4,608			841			4,294			5,074			2,274			5,100			11			22,202
Internal revenue		(65	)		(7	)		(99	)		–			(94	)		(3,058	)		–			(3,323	)
Revenue from external customersa		4,543			834			4,195			5,074			2,180			2,042			11			18,879
EBITDAb		1,055			173			1,414			479			755			2,659			(77	)		6,458
Depreciation and amortisation		(207	)		(146	)		(284	)		(422	)		(253	)		(1,301	)		(18	)		(2,631	)
Operating profit (loss)a		848			27			1,130			57			502			1,358			(95	)		3,827
Specific items (note 8)																							(212	)
Operating profit																							3,615
Net finance expensec																							(380	)
Share of post tax profit (loss) of associates and joint ventures																							6
Profit before tax																							3,241

^a Before specific items.

^b EBITDA is stated before specific items and is the group’s profitability measure for segments.

^c Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m). See note 8.

^d EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Summary of Internal Revenue and Costs Recorded by Each Reportable Segment

The tables below show internal revenue and costs recorded by each reportable segment.

	Internal cost recorded by
Year ended 31 March 2018	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–		24		20		4		–		18		66
EE		–		–		–		–		37		–		–		37
Business and Public Sector		62		2		–		32		19		–		–		115
Global Services		–		–		–		–		–		–		–		–
Wholesale and Ventures		1		2		13		10		–		42		66		134
Openreach		896		–		210		125		232		–		1,515		2,978
Total		959		4		247		187		292		42		1,599		3,330

	Internal cost recorded by
Year ended 31 March 2017	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–	21		20		4			–	18		63
EE		–		–		–		–		37		–		–		37
Business and Public Sector		60		3		–		39		20		–		–		122
Global Services		–		–		–		–		–		–		–		–
Wholesale and Ventures		–		–		2		23		–		39		74		138
Openreach		910		–		236		158		260		–		1,472		3,036
Total		970		3		259		240		321		39		1,564		3,396

	Internal cost recorded by
Year ended 31 March 2016	BT Consumer £m		EE £m		a	Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
BT Consumer		–		–			20		23		4		–		18		65
EEa		–		–			–		–		7		–		–		7
Business and Public Sector		60		1			–		18		19		1		–		99
Global Services		–		–			–		–		–		–		–		–
Wholesale and Ventures		–		12			5		22		–		55		–		94
Openreach		905		–			262		173		264		–		1,454		3,058
Total		965		13			287		236		294		56		1,472		3,323

^a EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Summary of Capital Expenditure

Capital expenditure

Year ended 31 March 2018	BT Consumer £m		EE £m		Business and Public Sector £m		Global Services £m		Wholesale and Ventures £m		Openreach £m		Other £m		Total £m
Intangible assets		106		130		93		92		87		70		64		642
Property, plant and equipment		185		498		211		186		142		1,588		70		2,880
Capital expenditurea		291		628		304		278		229		1,658		134		3,522

Year ended 31 March 2017	BT Consumer £m	EE £m	Business and Public Sector £m	Global Services £m	Wholesale and Ventures £m	Openreach £m		Other £m	Total £m
Intangible assets	92	133	64	126	77	74		55	621
Property, plant and equipment	145	483	211	235	149		1,499	111		2,833
Capital expenditurea	237	616	275	361	226		1,573	166		3,454

Year ended 31 March 2016	BT Consumer £m	EE £m	b	Business and Public Sector £m	Global Services £m	Wholesale and Ventures £m	Openreach £m		Other £m	Total £m
Intangible assets	88	29		36	62	70	62		65	412
Property, plant and equipment	119	67		117	293	139		1,385	90		2,210
Capital expenditurea	207	96		153	355	209		1,447	155		2,622

^a Net of government grants.

^b EE reflects results for the period from acquisition on 29 January 2016 to 31 March 2016.

Segment Revenue and Profit [Member]

Disclosure Of Nonadjusting Events After Reporting Period [Line Items]

Summary of Results of Reportable Segments

Segment revenue and profit

Year ended 31 March 2018	Consumer £m			Enterprise £m			Global Services £m			Openreach £m			Other £m			Total £m
Segment revenue		10,360			6,540			5,013			5,123			8			27,044
Internal revenue		(103	)		(217	)		–			(2,978	)		–			(3,298	)
Revenue from external customersa		10,257			6,323			5,013			2,145			8			23,746
EBITDAb		2,376			2,172			434			2,520			6			7,508
Depreciation and amortisation		(992	)		(676	)		(424	)		(1,360	)		(62	)		(3,514	)
Operating profit (loss)a		1,384			1,496			10			1,160			(56	)		3,994
Specific items																	(610	)
Operating profit																	3,384
Net finance expensec																	(579	)
Share of post tax loss of associates and joint ventures																	(1	)
Profit before tax																	2,804

^aBefore specific items.

^bEBITDA is stated before specific items and is the group’s profitability measure for segments.

^cNet finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

Year ended 31 March 2017	Consumer £m			Enterprise £m			Global Services £m			Openreach £m			Other £m			Total £m
Segment revenue		10,024			6,845			5,479			5,098			10			27,456
Internal revenue		(100	)		(238	)		–			(3,036	)		–			(3,374	)
Revenue from external customersa		9,924			6,607			5,479			2,062			10			24,082
EBITDAb		2,168			2,362			495			2,633			(10	)		7,648
Depreciation and amortisation		(989	)		(658	)		(439	)		(1,369	)		(55	)	(3,510)
Operating profit (loss)a		1,179			1,704			56			1,264			(65	)		4,138
Specific items																(968)
Operating profit																	3,170
Net finance expensec																	(610	)
Share of post tax loss of associates and joint ventures																	(9	)
Profit before tax																	2,551

Year ended 31 March 2016	Consumer £m			Enterprise £m			Global Services £m			Openreach £m			Other £m			Total £m
Segment revenue		5,449			6,544			5,074			5,100			11			22,178
Internal revenue		(72	)		(169	)		–			(3,058	)		–			(3,299	)
Revenue from external customersa		5,377			6,375			5,074			2,042			11			18,879
EBITDAb		1,228			2,169			479			2,659			(77	)		6,458
Depreciation and amortisation		(353	)		(537	)		(422	)		(1,301	)		(18	)		(2,631	)
Operating profit (loss)a		875			1,632			57			1,358			(95	)		3,827
Specific items																	(212	)
Operating profit																	3,615
Net finance expensec																	(380	)
Share of post tax loss of associates and joint ventures																	6
Profit before tax																	3,241

^aBefore specific items.

^bEBITDA is stated before specific items and is the group’s profitability measure for segments.

^cNet finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

Internal Revenue and Costs [Member]

Disclosure Of Nonadjusting Events After Reporting Period [Line Items]

Summary of Internal Revenue and Costs Recorded by Each Reportable Segment

Internal revenue and costs

Year ended 31 March 2018	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
Consumer		–		65		20		–		18		103
Enterprise		67		–		42		42		66		217
Global Services		–		–		–		–		–		–
Openreach		896		442		125		–		1,515		2,978
Total		963		507		187		42		1,599		3,298

Year ended 31 March 2017	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
Consumer		–		62		20		–		18		100
Enterprise		63		–		62		39		74		238
Global Services		–		–		–		–		–		–
Openreach		910		496		158		–		1,472		3,036
Total		973		558		240		39		1,564		3,374

Year ended 31 March 2016	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Internal revenue recorded by
Consumer		–		31		23		–		18		72
Enterprise		73		–		40		56		–		169
Global Services		–		–		–		–		–		–
Openreach		905		526		173		–		1,454		3,058
Total		978		557		236		56		1,472		3,299

Capital Expenditure [Member]

Disclosure Of Nonadjusting Events After Reporting Period [Line Items]

Summary of Capital Expenditure

Capital expenditure

Year ended 31 March 2018	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Intangible assets		236		180		92		70		64		642
Property, plant and equipment		683		353		186		1,588		70		2,880
Capital expenditurea		919		533		278		1,658		134		3,522

Year ended 31 March 2017	Consumer £m		BT Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Intangible assets		225		141		126		74		55		621
Property, plant and equipment		628		360		235		1,499		111		2,833
Capital expenditurea		853		501		361		1,573		166		3,454

Year ended 31 March 2016	Consumer £m		Enterprise £m		Global Services £m		Openreach £m		Other £m		Total £m
Intangible assets		117		106		62		62		65		412
Property, plant and equipment		186		256		293		1,385		90		2,210
Capital expenditurea		303		362		355		1,447		155		2,622

^aNet of government grants.

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Basis of Preparation - Additional Information (Detail) - Retained Earnings (Loss) [Member] - Financial Impact [Member] £ in Billions	Apr. 01, 2018 GBP (£)
Bottom of Range [Member]
Disclosure Of Basis Of Preparation Of Financial Statements [Line Items]
Cumulative increase in retained earnings	£ 1.1
Top of Range [Member]
Disclosure Of Basis Of Preparation Of Financial Statements [Line Items]
Cumulative increase in retained earnings	£ 1.5

XML

Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Mar. 31, 2018 Segment
Significant Accounting Policies [Abstract]
Number of operating segments	4
Cash and cash equivalents original maturity period	three months or less

XML

Significant Accounting Policies - Summary of Estimated Useful Lives Assigned to Principal Categories of Assets (Detail)	12 Months Ended
	Mar. 31, 2018
Freehold Buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	14 to 50 years
Short-Term Leasehold Improvements [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	Shorter of 10 years or lease term
Leasehold Land and Buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	Unexpired portion of lease or 40 years, whichever is the shorter
Network Infrastructure [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	more than 18 years
Network Infrastructure [Member] | Duct [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	40 years
Network Infrastructure [Member] | Cable [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	3 to 25 years
Network Infrastructure [Member] | Fibre Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	5 to 20 years
Network Infrastructure [Member] | Exchange Equipment [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	2 to 13 years
Network Infrastructure [Member] | Other Network Equipment [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	2 to 20 years
Motor Vehicles [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	2 to 9 years
Computers and Office Equipment [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Estimated useful lives of property, plant and equipment	3 to 7 years

XML

Significant Accounting Policies - Summary of Estimated Useful Economic Lives Assigned to Principal Categories of Intangible Assets (Detail)	12 Months Ended
	Mar. 31, 2018
Computer Software [Member]
Disclosure of detailed information about intangible assets [Line Items]
Estimated useful economic lives of intangible assets	2 to 10 years
Telecommunications Licences [Member]
Disclosure of detailed information about intangible assets [Line Items]
Estimated useful economic lives of intangible assets	2 to 20 years
Customer Relationships and Brands [Member]
Disclosure of detailed information about intangible assets [Line Items]
Estimated useful economic lives of intangible assets	1 to 15 years

XML

Segment Information - Summary of Results of Reportable Segments (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of operating segments [Line Items]
Revenue		£ 23,723	£ 24,062	£ 19,012
Depreciation and amortisation		(3,514)	(3,510)	(2,631)
Operating profit (loss)		3,384	3,170	3,615
Net finance expense	[1]	(579)	(610)	(380)
Share of post tax profit (loss) of associates and joint ventures		(1)	(9)	6
Profit (loss) before taxation		2,804	2,551	3,241
Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue	[2]	23,746	24,082	18,879
EBITDA		7,508	7,648	6,458
Depreciation and amortisation		(3,514)	(3,510)	(2,631)
Operating profit (loss)	[2]	3,994	4,138	3,827
Net finance expense		(361)	(400)	(151)
Share of post tax profit (loss) of associates and joint ventures		(1)	(9)	6
Profit (loss) before taxation		3,632	3,729	3,682
Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue	[3]	(23)	(20)	133
Operating profit (loss)	[3]	(610)	(968)	(212)
Net finance expense	[3]	(218)	(210)	(229)
Profit (loss) before taxation	[3]	(828)	(1,178)	(441)
Segment Revenue [Member]
Disclosure of operating segments [Line Items]
Revenue		27,044	27,456	22,178
Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		27,076	27,478	22,202
Internal Revenue [Member]
Disclosure of operating segments [Line Items]
Revenue		3,330	3,396	3,323
Internal Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		(3,330)	(3,396)	(3,323)
BT Consumer [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		5,000	4,871	4,543
EBITDA		1,023	1,012	1,055
Depreciation and amortisation		(216)	(209)	(207)
Operating profit (loss)		807	803	848
BT Consumer [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		5,066	4,934	4,608
BT Consumer [Member] | Internal Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		(66)	(63)	(65)
EE [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		5,257	5,053	834
EBITDA		1,353	1,156	173
Depreciation and amortisation		(776)	(780)	(146)
Operating profit (loss)		577	376	27
EE [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		5,294	5,090	841
EE [Member] | Internal Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		(37)	(37)	(7)
Business and Public Sector [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		4,448	4,636	4,195
EBITDA		1,418	1,528	1,414
Depreciation and amortisation		(365)	(352)	(284)
Operating profit (loss)		1,053	1,176	1,130
Business and Public Sector [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		4,563	4,758	4,294
Business and Public Sector [Member] | Internal Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		(115)	(122)	(99)
Global Services [Member]
Disclosure of operating segments [Line Items]
Depreciation and amortisation		(424)	(439)	(422)
Global Services [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue	[2]	5,013	5,479	5,074
EBITDA		434	495	479
Depreciation and amortisation		(424)	(439)	(422)
Operating profit (loss)	[2]	10	56	57
Global Services [Member] | Segment Revenue [Member]
Disclosure of operating segments [Line Items]
Revenue		5,013	5,479	5,074
Global Services [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		5,013	5,479	5,074
Wholesale and Ventures [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		1,875	1,971	2,180
EBITDA		754	834	755
Depreciation and amortisation		(311)	(306)	(253)
Operating profit (loss)		443	528	502
Wholesale and Ventures [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		2,009	2,109	2,274
Wholesale and Ventures [Member] | Internal Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		(134)	(138)	(94)
Openreach [Member]
Disclosure of operating segments [Line Items]
Depreciation and amortisation		(1,360)	(1,369)	(1,301)
Openreach [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue	[2]	2,145	2,062	2,042
EBITDA		2,520	2,633	2,659
Depreciation and amortisation		(1,360)	(1,369)	(1,301)
Operating profit (loss)	[2]	1,160	1,264	1,358
Openreach [Member] | Segment Revenue [Member]
Disclosure of operating segments [Line Items]
Revenue		5,123	5,098	5,100
Openreach [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		5,123	5,098	5,100
Openreach [Member] | Internal Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		(2,978)	(3,036)	(3,058)
Other [Member]
Disclosure of operating segments [Line Items]
Depreciation and amortisation		(62)	(55)	(18)
Other [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue	[2]	8	10	11
EBITDA		6	(10)	(77)
Depreciation and amortisation		(62)	(55)	(18)
Operating profit (loss)	[2]	(56)	(65)	(95)
Other [Member] | Segment Revenue [Member]
Disclosure of operating segments [Line Items]
Revenue		8	10	11
Other [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure of operating segments [Line Items]
Revenue		£ 8	£ 10	£ 11

[1] Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

[2] Before specific items.

[3] a For a definition of specific items, see page 209. An analysis of specific items is provided in note 8.

XML

Segment Information - Summary of Results of Reportable Segments (Parenthetical) (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of operating segments [Line Items]
Net finance expense	[1]	£ 579	£ 610	£ 380
Specific Items [Member]
Disclosure of operating segments [Line Items]
Net finance expense	[2]	£ 218	£ 210	£ 229

[1] Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

[2] a For a definition of specific items, see page 209. An analysis of specific items is provided in note 8.

XML

Segment Information - Summary of Internal Revenue and Costs Recorded by Each Reportable Segment (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Internal revenue recorded by
Internal cost	£ 20,339	£ 20,892	£ 15,397
Internal revenue	23,723	24,062	19,012
Elimination of Intersegment Amounts [Member]
Internal revenue recorded by
Internal revenue	3,330	3,396	3,323
Elimination of Intersegment Amounts [Member] | Global Services [Member]
Internal revenue recorded by
Internal cost	187	240	236
Elimination of Intersegment Amounts [Member] | Other [Member]
Internal revenue recorded by
Internal cost	1,599	1,564	1,472
Elimination of Intersegment Amounts [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal cost	959	970	965
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal cost	62	60	60
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	1
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Openreach [Member]
Internal revenue recorded by
Internal cost	896	910	905
Elimination of Intersegment Amounts [Member] | EE [Member]
Internal revenue recorded by
Internal cost	4	3	13
Elimination of Intersegment Amounts [Member] | EE [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal cost	2	3	1
Elimination of Intersegment Amounts [Member] | EE [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	2		12
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal cost	247	259	287
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal cost	24	21	20
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	13	2	5
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | Openreach [Member]
Internal revenue recorded by
Internal cost	210	236	262
Elimination of Intersegment Amounts [Member] | Global Services [Member]
Internal revenue recorded by
Internal cost	187	240	236
Elimination of Intersegment Amounts [Member] | Global Services [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal cost	20	20	23
Elimination of Intersegment Amounts [Member] | Global Services [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal cost	32	39	18
Elimination of Intersegment Amounts [Member] | Global Services [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	10	23	22
Elimination of Intersegment Amounts [Member] | Global Services [Member] | Openreach [Member]
Internal revenue recorded by
Internal cost	125	158	173
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	292	321	294
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal cost	4	4	4
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | EE [Member]
Internal revenue recorded by
Internal cost	37	37	7
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal cost	19	20	19
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | Openreach [Member]
Internal revenue recorded by
Internal cost	232	260	264
Elimination of Intersegment Amounts [Member] | Openreach [Member]
Internal revenue recorded by
Internal cost	42	39	56
Internal revenue	2,978	3,036	3,058
Elimination of Intersegment Amounts [Member] | Openreach [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal cost			1
Elimination of Intersegment Amounts [Member] | Openreach [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	42	39	55
Elimination of Intersegment Amounts [Member] | Openreach [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal revenue	896	910	905
Elimination of Intersegment Amounts [Member] | Openreach [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal revenue	210	236	262
Elimination of Intersegment Amounts [Member] | Openreach [Member] | Global Services [Member]
Internal revenue recorded by
Internal revenue	125	158	173
Elimination of Intersegment Amounts [Member] | Openreach [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal revenue	232	260	264
Elimination of Intersegment Amounts [Member] | Openreach [Member] | Other [Member]
Internal revenue recorded by
Internal revenue	1,515	1,472	1,454
Elimination of Intersegment Amounts [Member] | Other [Member]
Internal revenue recorded by
Internal cost	1,599	1,564	1,472
Elimination of Intersegment Amounts [Member] | Other [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal cost	18	18	18
Elimination of Intersegment Amounts [Member] | Other [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal cost	66	74
Elimination of Intersegment Amounts [Member] | Other [Member] | Openreach [Member]
Internal revenue recorded by
Internal cost	1,515	1,472	1,454
Elimination of Intersegment Amounts [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal revenue	66	63	65
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal revenue	24	21	20
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Global Services [Member]
Internal revenue recorded by
Internal revenue	20	20	23
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal revenue	4	4	4
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Other [Member]
Internal revenue recorded by
Internal revenue	18	18	18
Elimination of Intersegment Amounts [Member] | EE [Member]
Internal revenue recorded by
Internal revenue	37	37	7
Elimination of Intersegment Amounts [Member] | EE [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal revenue	37	37	7
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal revenue	115	122	99
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | Openreach [Member]
Internal revenue recorded by
Internal revenue			1
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal revenue	62	60	60
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | EE [Member]
Internal revenue recorded by
Internal revenue	2	3	1
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | Global Services [Member]
Internal revenue recorded by
Internal revenue	32	39	18
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal revenue	19	20	19
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member]
Internal revenue recorded by
Internal revenue	134	138	94
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | Openreach [Member]
Internal revenue recorded by
Internal revenue	42	39	55
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | BT Consumer [Member]
Internal revenue recorded by
Internal revenue	1
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | EE [Member]
Internal revenue recorded by
Internal revenue	2		12
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | Business and Public Sector [Member]
Internal revenue recorded by
Internal revenue	13	2	5
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | Global Services [Member]
Internal revenue recorded by
Internal revenue	10	23	£ 22
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member] | Other [Member]
Internal revenue recorded by
Internal revenue	£ 66	£ 74

XML

Segment Information - Summary of Revenue by Products and Services (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of products and services [Line Items]
Revenue		£ 23,723	£ 24,062	£ 19,012
Before Specific Items [Member]
Disclosure of products and services [Line Items]
Revenue	[1]	23,746	24,082	18,879
Before Specific Items [Member] | ICT and Managed Networks [Member]
Disclosure of products and services [Line Items]
Revenue		5,530	5,927	6,193
Before Specific Items [Member] | Broadband and TV [Member]
Disclosure of products and services [Line Items]
Revenue		4,655	4,477	3,535
Before Specific Items [Member] | Mobile [Member]
Disclosure of products and services [Line Items]
Revenue		6,451	6,358	1,326
Before Specific Items [Member] | Calls, Lines and Connections [Member]
Disclosure of products and services [Line Items]
Revenue		5,126	5,069	5,920
Before Specific Items [Member] | Transit [Member]
Disclosure of products and services [Line Items]
Revenue		265	404	419
Before Specific Items [Member] | Other Products and Services [Member]
Disclosure of products and services [Line Items]
Revenue		£ 1,719	£ 1,847	£ 1,486

[1] Before specific items.

XML

Segment Information - Summary of Capital Expenditure (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of operating segments [Line Items]
Capital expenditure	£ 3,522	£ 3,454	£ 2,622
Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	2,880	2,833	2,210
Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	642	621	412
BT Consumer [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	291	237	207
BT Consumer [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	185	145	119
BT Consumer [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	106	92	88
EE [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	628	616	96
EE [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	498	483	67
EE [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	130	133	29
Business and Public Sector [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	304	275	153
Business and Public Sector [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	211	211	117
Business and Public Sector [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	93	64	36
Global Services [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	278	361	355
Global Services [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	186	235	293
Global Services [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	92	126	62
Wholesale and Ventures [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	229	226	209
Wholesale and Ventures [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	142	149	139
Wholesale and Ventures [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	87	77	70
Openreach [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	1,658	1,573	1,447
Openreach [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	1,588	1,499	1,385
Openreach [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	70	74	62
Other [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	134	166	155
Other [Member] | Property, Plant and Equipment [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	70	111	90
Other [Member] | Intangible Assets [Member]
Disclosure of operating segments [Line Items]
Capital expenditure	£ 64	£ 55	£ 65

XML

Segment Information - Summary of Geographic Information by Revenue from External Customers and Non-Current Assets (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of geographical areas [Line Items]
Revenue		£ 23,723	£ 24,062	£ 19,012
Before Specific Items [Member]
Disclosure of geographical areas [Line Items]
Revenue	[1]	23,746	24,082	18,879
Non-current assets		31,810	31,926	31,671
UK [Member] | Before Specific Items [Member]
Disclosure of geographical areas [Line Items]
Revenue		19,687	19,421	14,814
Non-current assets		28,843	28,818	28,583
Europe, Middle East and Africa, Excluding the UK [Member] | Before Specific Items [Member]
Disclosure of geographical areas [Line Items]
Revenue		2,489	2,841	2,442
Non-current assets		2,527	2,535	2,349
Asia Pacific [Member] | Before Specific Items [Member]
Disclosure of geographical areas [Line Items]
Revenue		574	672	612
Non-current assets		109	149	191
Americas [Member] | Before Specific Items [Member]
Disclosure of geographical areas [Line Items]
Revenue		996	1,148	1,011
Non-current assets		£ 331	£ 424	£ 548

[1] Before specific items.

XML

Operating Costs - Summary of Operating Costs (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Operating Costs [Line Items]
Wages and salaries		£ 4,223	£ 4,128	£ 3,684
Social security costs		461	477	398
Other pension costs		624	521	494
Share-based payment expense		84	57	58
Total staff costs		5,392	5,183	4,634
Own work capitalised		(798)	(813)	(720)
Net staff costs		4,594	4,370	3,914
Net indirect labour costs		315	399	304
Net labour costs		4,909	4,769	4,218
Payments to telecommunications operators		2,306	2,653	2,183
Property and energy costs		1,285	1,202	1,024
Network operating and IT costs		963	983	644
TV programme rights charges		763	714	544
Other operating costs		6,234	6,298	4,023
Other operating income		(222)	(185)	(215)
Amortisation of intangible assets		1,123	1,118	621
Internal cost		20,339	20,892	15,397
Operating costs before specific items include the following:
Leaver costs		50	86	109
Research and development expenditure		632	638	574
Operating lease charges		732	692	441
Foreign currency gains			(12)	(1)
Government grants		(3)	(5)	(6)
Owned Property Plant and Equipment [Member]
Disclosure Of Operating Costs [Line Items]
Owned assets		2,381	2,382	2,000
Finance Leased Property Plant and Equipment [Member]
Disclosure Of Operating Costs [Line Items]
Owned assets		10	10	10
Before Specific Items [Member]
Disclosure Of Operating Costs [Line Items]
Internal cost		19,752	19,944	15,052
Specific Items [Member]
Disclosure Of Operating Costs [Line Items]
Internal cost	[1]	£ 587	£ 948	£ 345

[1] a For a definition of specific items, see page 209. An analysis of specific items is provided in note 8.

XML

Operating Costs - Summary of Operating Costs (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Operating Costs [Line Items]
Net of capitalised indirect labour costs	£ 612	£ 463	£ 430
Leaver costs associated with restructuring and integration	168	37	0
Internal cost	20,339	20,892	15,397
Internally Developed Computer Software and Operating Expenses [Member]
Disclosure Of Operating Costs [Line Items]
Internal cost	59	61	73
Internally Developed Software [Member]
Disclosure Of Operating Costs [Line Items]
Amortisation relating to write off of software costs	573	577	501
Capitalised Software Development Costs [Member]
Disclosure Of Operating Costs [Line Items]
Internal cost	450	457	399
Specific Item [Member]
Disclosure Of Operating Costs [Line Items]
Amortisation relating to write off of software costs	£ 0	£ 62	£ 0

XML

Operating Costs - Summary of Compensation of Key Management Personnel (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Operating Costs [Abstract]
Short-term employee benefits	£ 12.4	£ 10.9	£ 10.3
Post employment benefits	1.4	1.4	1.2
Share-based payments	6.6	5.8	5.9
Termination benefits	2.2		0.6
Compensation of key management personnel	£ 22.6	£ 18.1	£ 18.0

XML

Employees - Summary of Number of Employees in the Group (Detail) - Employee	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	105,800	106,400	102,500
Average	106,200	105,000	91,000
BT Consumer [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	8,800	8,700	6,700
Average	8,800	7,700	6,300
EE [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	9,400	9,200	9,000
Average	9,200	9,100	1,300
Business and Public Sector [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	10,100	10,300	10,300
Average	10,300	10,200	9,300
Global Services [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	16,900	17,500	16,800
Average	17,300	17,400	16,500
Wholesale and Ventures [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	3,800	3,800	3,700
Average	3,900	3,700	3,800
Openreach [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	30,500	30,200	31,500
Average	30,400	30,900	32,100
Other [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	26,300	26,700	24,500
Average	26,300	26,000	21,700
UK [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	82,200	82,800	81,400
Average	82,500	82,200	71,800
Non-United Kingdom [Member]
Disclosure Of Number And Average Number Of Employees [Line Items]
Year end	23,600	23,600	21,100
Average	23,700	22,800	19,200

XML

Audit, Audit Related and Other Non-Audit Services - Summary of Fees Paid or Payable to Company's Auditors (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Auditor Remuneration [Line Items]
Audit services fees	£ 11,238	£ 9,935	£ 8,944
Other services fees	803	3,009	3,844
Total services	13,672	14,809	14,998
British Telecommunications plc [Member]
Auditor Remuneration [Line Items]
Audit services fees	5,372	4,271	3,871
Subsidiaries [Member]
Auditor Remuneration [Line Items]
Audit services fees	5,866	5,664	5,073
Audit Related Assurance Services [Member]
Auditor Remuneration [Line Items]
Other services fees	1,631	1,865	2,210
Tax Compliance Services [Member]
Auditor Remuneration [Line Items]
Taxation services fees		366	412
Tax Advisory Services [Member]
Auditor Remuneration [Line Items]
Taxation services fees		111	156
Other Assurance Services [Member]
Auditor Remuneration [Line Items]
Other services fees	211	200	1,611
All Other Non Audit Services [Member]
Auditor Remuneration [Line Items]
Other services fees	£ 592	£ 2,332	£ 1,665

XML

Audit, Audit Related and Other Non-Audit Services - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
BT Pension Scheme [Member]
Auditor Remuneration [Line Items]
Total fees paid to auditors	£ 2.1	£ 2.1	£ 1.7

XML

Audit, Audit Related and Other Non-Audit Services - Summary of Total Fees Received by Company's Auditors from the BT Pension Scheme (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Auditor Remuneration [Line Items]
Audit services fees	£ 11,238	£ 9,935	£ 8,944
Audit related assurance services	803	3,009	3,844
Total services	13,672	14,809	14,998
Audit Related Assurance Services [Member]
Auditor Remuneration [Line Items]
Audit related assurance services	1,631	1,865	2,210
Tax Compliance Services [Member]
Auditor Remuneration [Line Items]
Taxation services fees		366	412
Tax Advisory Services [Member]
Auditor Remuneration [Line Items]
Taxation services fees		111	156
All Other Non Audit Services [Member]
Auditor Remuneration [Line Items]
Audit related assurance services	592	2,332	1,665
BT Pension Scheme [Member]
Auditor Remuneration [Line Items]
Total services	2,137	2,122	1,705
BT Pension Scheme [Member] | Audit Of Financial Statements Of Associates [Member]
Auditor Remuneration [Line Items]
Audit services fees	345	251	213
BT Pension Scheme [Member] | Audit Related Assurance Services [Member]
Auditor Remuneration [Line Items]
Audit related assurance services			10
BT Pension Scheme [Member] | Tax Compliance Services [Member]
Auditor Remuneration [Line Items]
Taxation services fees	153	210	198
BT Pension Scheme [Member] | Tax Advisory Services [Member]
Auditor Remuneration [Line Items]
Taxation services fees	1,074	493	681
BT Pension Scheme [Member] | All Other Non Audit Services [Member]
Auditor Remuneration [Line Items]
Audit related assurance services	£ 565	£ 1,168	£ 603

XML

Specific Items - Summary of Specific Items (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Revenue
Total revenue		£ (23,723)	£ (24,062)	£ (19,012)
Operating costs
Profit on disposal of businesses		1	16
Operating costs		20,339	20,892	15,397
Operating loss		(3,384)	(3,170)	(3,615)
Net finance expense
Total net finance expense	[1]	579	610	380
Net specific items charge before tax		(2,804)	(2,551)	(3,241)
Taxation
Tax credit on re-measurement of deferred tax			(63)
Total taxation		620	485	508
Net specific items charge after tax		(2,184)	(2,066)	(2,733)
Specific Items [Member]
Revenue
Italian business investigation			22
Regulatory matters		23	(2)	(203)
EE fair value adjustment				70
Total revenue		23	20	(133)
Operating costs
EE acquisition warranty claims		225	0	0
Restructuring charges		241	0	0
EE acquisition and integration costs		46	215	113
Property rationalisation costs		28	0	29
Regulatory matters		26	481	203
Italian business investigation		22	238
Out of period irrecoverable VAT			30
Profit on disposal of businesses		(1)	(16)
Operating costs		587	948	345
Operating loss		610	968	212
Net finance expense
Interest expense on retirement benefit obligation		218	209	221
EE related finance cost				8
Interest on out of period irrecoverable VAT			1
Total net finance expense		218	210	229
Net specific items charge before tax		828	1,178	441
Taxation
Tax credit on specific items above		(87)	(154)	(70)
Tax credit on re-measurement of deferred tax			(63)	(96)
Total taxation		(87)	(217)	(166)
Net specific items charge after tax		£ 741	£ 961	£ 275

[1] Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

XML

Specific Items - Additional Information (Detail) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Specific Items [Line Items]
Total expected cost related to projects in first phase	£ 300,000,000
Amortisation charge relating to write-off of IT assets	400,000,000
Deemed consent charge, net	300,000,000
Ladder pricing agreements costs recognised		8,000,000	£ 203,000,000
Provision recognized	133,000,000	536,000,000
Regulatory [Member]
Disclosure Of Specific Items [Line Items]
Provision recognized	51,000,000	426,000,000
Specific Items [Member]
Disclosure Of Specific Items [Line Items]
EE acquisition warranty claim	225,000,000	0	0
Restructuring charges	241,000,000	0	0
EE acquisition and integration costs	46,000,000	215,000,000	113,000,000
Amortisation charge relating to write-off of IT assets		62,000,000	0
Property rationalisation costs	28,000,000	0	29,000,000
Regulatory matters effect	49,000,000	479,000,000	0
Regulatory matters revenue	23,000,000	(2,000,000)	(203,000,000)
Regulatory costs recognised as specific items	26,000,000
Deemed consent charge		342,000,000	0
Regulatory matters effect		42,000,000
Deemed consent charge, net		300,000,000
Ladder pricing agreements revenue recognised		8,000,000	203,000,000
Fees incurred related to investigation of specific items	22,000,000	15,000,000
Charge recognised related to investigation of specific items		245,000,000
Profit on disposal of businesses	1,000,000	16,000,000	0
EE fair value adjustment			£ 70,000,000
Out of period irrecoverable VAT		30,000,000
Interest on out of period irrecoverable VAT		1,000,000
Specific Items [Member] | Regulatory [Member]
Disclosure Of Specific Items [Line Items]
Increase in net charge	49,000,000	£ 137,000,000
Provision recognized	51,000,000
Release of amount in trade and other payables	£ 2,000,000

XML

Taxation - Additional Information (Detail) - GBP (£)			12 Months Ended
	Apr. 01, 2020	Apr. 01, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Income Tax Expense [Line Items]
Approximate percentage of provision under tax authority examination			80.00%
Provision for tax uncertainties included in current tax liabilities			£ 240,000,000	£ 281,000,000
Additional amount required for tax settlement			£ 471,000,000
Corporation tax		19.00%	17.00%	17.00%	19.00%
Deferred tax credit specific item recognised				£ 63,000,000
Unused tax losses for which no deferred tax asset recognised			£ 4,100,000,000	4,400,000,000
Undistributed earnings			11,327,000,000	7,163,000,000	£ 9,761,000,000
UK [Member]
Disclosure Of Income Tax Expense [Line Items]
Current tax expense			(614,000,000)	(594,000,000)	(684,000,000)
Unused tax losses for which no deferred tax asset recognised			16,900,000,000	17,000,000,000
Income tax			23,000,000	26,200,000
Non-United Kingdom [Member]
Disclosure Of Income Tax Expense [Line Items]
Current tax expense			(66,000,000)	(109,000,000)	£ (80,000,000)
Deferred tax liability			0
Undistributed earnings			2,400,000,000	£ 3,500,000,000
European Union [Member]
Disclosure Of Income Tax Expense [Line Items]
Undistributed earnings			940,000,000
Additional income tax			23,900,000
Events After Reporting Period [Member]
Disclosure Of Income Tax Expense [Line Items]
Corporation tax	17.00%
EE [Member]
Disclosure Of Income Tax Expense [Line Items]
Deferred tax asset on historical tax losses			92,000,000
Current tax expense			£ 382,000,000

XML

Taxation - Analysis of Our Taxation Expenses (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Income Tax Expense [Line Items]
Origination and reversal of temporary differences	£ 46	£ 96	£ 70
Adjustments in respect of earlier years	(57)	26	2
Total current tax expense	(620)	(670)	(676)
Impact of change in UK corporation tax rate to 17% (2016/17: 17%, 2015/16: 19%)		63	96
Remeasurement of temporary differences	11
Total deferred taxation credit		185	168
Total taxation expense	(620)	(485)	(508)
UK [Member]
Disclosure Of Income Tax Expense [Line Items]
Current	(614)	(594)	(684)
Adjustments in respect of earlier years	37	33	59
Non-United Kingdom [Member]
Disclosure Of Income Tax Expense [Line Items]
Current	(66)	£ (109)	(80)
Adjustments in respect of earlier years	£ 23		£ 29

XML

Taxation - Analysis of Our Taxation Expenses (Parenthetical) (Detail)		12 Months Ended
	Apr. 01, 2017	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Income Tax Expense [Line Items]
Change in corporation tax rate	19.00%	17.00%	17.00%	19.00%
UK [Member]
Disclosure Of Income Tax Expense [Line Items]
Corporation tax rate		19.00%	20.00%	20.00%

XML

Taxation - Summary of Factors Affecting Our Taxation Expense for the Year (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Factors Affecting Our Taxation Expense For The Year [Abstract]
Profit before taxation	£ 2,804	£ 2,551	£ 3,241
Expected taxation expense at UK rate of 19% (2016/17: 20%, 2015/16: 20%)	(533)	(510)	(648)
(Higher) lower taxes on non-UK profits	(8)	(29)	4
Net permanent differences between tax and accounting	(100)	(183)	(12)
Adjustments in respect of earlier years	3	59	90
Prior year non-UK losses used against current year profits	16	120	9
Non-UK losses not recognised	(9)	(8)	(34)
Other deferred tax assets not recognised			6
Lower taxes on profit on disposal of business		3
Re-measurement of deferred tax balances	11	63	96
Other non-recurring items			(19)
Total taxation expense	(620)	(485)	(508)
Exclude specific items (note 8)	(87)	(217)	(166)
Total taxation expense before specific items	£ (707)	£ (702)	£ (674)

XML

Taxation - Summary of Factors Affecting Our Taxation Expense for the Year (Parenthetical) (Detail)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Factors Affecting Our Taxation Expense For The Year [Abstract]
Tax rate	19.00%	20.00%	20.00%

XML

Taxation - Summary of Tax Components of Other Comprehensive Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Relating To Components Of Other Comprehensive Income [Abstract]
Pension remeasurements	£ (346)	£ 416	£ (240)
Exchange differences on translation of foreign operations	(9)	21	38
Fair value movements on cash flow hedges - net fair value gains or losses	57	(131)	(72)
Fair value movements on cash flow hedges - recognised in income and expense	(47)	139	39
Income tax relating to components of other comprehensive income	(345)	445	(235)
Current tax credit	203	122	231
Deferred tax (expense) credit	(548)	323	(466)
Total income tax expense	£ (345)	£ 445	£ (235)

XML

Taxation - Summary of Tax Components of Other Comprehensive Income (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Income Tax Relating To Components Of Other Comprehensive Income [Abstract]
Current tax credit includes cash contributions made to reduce retirement benefit obligations	£ 212	£ 110	£ 217

XML

Taxation - Summary of Tax (Expense) Credit Recognised Directly in Equity (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Tax Expense Credit Recognised Directly In Equity [Abstract]
Tax (expense) credit relating to share-based payments	£ (2)	£ (6)	£ 12

XML

Taxation - Summary of Deferred Taxation (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Beginning balance	£ (477)	£ 15
(Credit) expense recognised in the income statement		(185)
(Credit) expense recognised in other comprehensive income	548	(323)
Expense recognised in equity	6	23
Exchange differences	3	(7)
Transfer to current tax	17
Ending balance	97	(477)
Deferred tax asset	(1,243)	(1,717)	£ (1,247)
Deferred tax liability	1,340	1,240	£ 1,262
Fixed Asset Temporary Differences [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Beginning balance	1,432	1,618
(Credit) expense recognised in the income statement	11	(181)
(Credit) expense recognised in other comprehensive income		(5)
Transfer to current tax	17
Ending balance	1,460	1,432
Deferred tax asset	(41)	(117)
Deferred tax liability	1,501	1,549
Retirement Benefit Obligations [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Beginning balance	(1,537)	(1,149)
(Credit) expense recognised in the income statement	(104)	(82)
(Credit) expense recognised in other comprehensive income	558	(306)
Ending balance	(1,083)	(1,537)
Deferred tax asset	(1,083)	(1,537)
Share-Based Payments [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Beginning balance	(17)	(54)
(Credit) expense recognised in the income statement	4	14
Expense recognised in equity	6	23
Ending balance	(7)	(17)
Deferred tax asset	(7)	(17)
Tax Losses [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Beginning balance	(270)	(325)
(Credit) expense recognised in the income statement	89	65
(Credit) expense recognised in other comprehensive income		(3)
Exchange differences	(2)	(7)
Ending balance	(183)	(270)
Deferred tax asset	(183)	(270)
Other [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Beginning balance	(85)	(75)
(Credit) expense recognised in the income statement		(1)
(Credit) expense recognised in other comprehensive income	(10)	(9)
Exchange differences	5
Ending balance	(90)	(85)
Deferred tax asset	(90)	(96)
Deferred tax liability		11
Jurisdictional Offset [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Deferred tax asset	161	320
Deferred tax liability	£ (161)	£ (320)

XML

Taxation - Summary of Deferred Taxation (Parenthetical) (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Total deferred tax	£ (97)	£ 477	£ (15)
Defined Contribution Plan [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [Line Items]
Total deferred tax	£ 2	£ 2

XML

Taxation - Summary of Restricted Loss (Detail) £ in Millions	12 Months Ended
	Mar. 31, 2018 GBP (£)
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Total restricted losses	£ 220
Unrestricted operating losses	3,784
Other temporary differences	77
Total	4,081
Europe [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Total restricted losses	£ 14
Europe [Member] | Bottom of Range [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Deferred tax assets restricted losses expiry date	2019
Europe [Member] | Top of Range [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Deferred tax assets restricted losses expiry date	2027
Americas [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Total restricted losses	£ 204
Americas [Member] | Bottom of Range [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Deferred tax assets restricted losses expiry date	2019
Americas [Member] | Top of Range [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Deferred tax assets restricted losses expiry date	2037
Other Countries [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Total restricted losses	£ 2
Other Countries [Member] | Bottom of Range [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Deferred tax assets restricted losses expiry date	2019
Other Countries [Member] | Top of Range [Member]
Disclosure Of Unrecognised Tax Losses And Other Temporary Differences [Line Items]
Deferred tax assets restricted losses expiry date	2027

XML

Dividends - Additional Information (Detail) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Apr. 01, 2018
Disclosure Of Dividends Paid And Proposed [Line Items]
Dividends paid		£ 2,350,000,000	£ 1,450,000,000
BT Group Investments Limited [Member]
Disclosure Of Dividends Paid And Proposed [Line Items]
Dividends paid	£ 0	2,350,000,000	1,450,000,000
Final dividend declared		£ 0	£ 2,350,000,000
BT Group Investments Limited [Member] | Events After Reporting Period [Member]
Disclosure Of Dividends Paid And Proposed [Line Items]
Final dividend declared				£ 2,500,000,000

XML

Intangible Assets - Summary of Intangible Assets (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	£ 15,037	£ 15,458
Ending balance	14,455	15,037
Gross Carrying Amount [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	20,625	19,929
Acquisitions	17	5
Additions	642	621
Disposals and adjustments	(474)	(152)
Transfers		(4)
Exchange differences	(100)	226
Ending balance	20,710	20,625
Accumulated Depreciation and Amortisation [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	5,588	4,471
Charge for the year	1,123	1,180
Disposals and adjustments	(465)	(121)
Exchange differences	9	58
Ending balance	6,255	5,588
Goodwill [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	8,042
Ending balance	7,953	8,042
Goodwill [Member] | Gross Carrying Amount [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	8,042	7,915
Acquisitions	14	5
Disposals and adjustments	(3)	(23)
Exchange differences	(100)	145
Ending balance	7,953	8,042
Customer Relationships and Brands [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	2,609
Ending balance	2,219	2,609
Customer Relationships and Brands [Member] | Gross Carrying Amount [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	3,422	3,401
Exchange differences	(12)	21
Ending balance	3,410	3,422
Customer Relationships and Brands [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	813	418
Charge for the year	379	383
Exchange differences	(1)	12
Ending balance	1,191	813
Telecoms Licences and Other [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	2,665
Ending balance	2,530	2,665
Telecoms Licences and Other [Member] | Gross Carrying Amount [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	2,945	2,930
Acquisitions	3
Disposals and adjustments	(3)
Exchange differences	6	15
Ending balance	2,951	2,945
Telecoms Licences and Other [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	280	131
Charge for the year	141	140
Disposals and adjustments	(3)
Exchange differences	3	9
Ending balance	421	280
Internally Developed Software [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	1,170
Ending balance	1,142	1,170
Internally Developed Software [Member] | Gross Carrying Amount [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	4,363	4,073
Additions	517	483
Disposals and adjustments	(55)	(131)
Transfers		(66)
Exchange differences	(3)	4
Ending balance	4,822	4,363
Internally Developed Software [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	3,193	2,747
Charge for the year	525	556
Disposals and adjustments	(36)	(114)
Exchange differences	(2)	4
Ending balance	3,680	3,193
Purchased Software [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	551
Ending balance	611	551
Purchased Software [Member] | Gross Carrying Amount [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	1,853	1,610
Additions	125	138
Disposals and adjustments	(413)	2
Transfers		62
Exchange differences	9	41
Ending balance	1,574	1,853
Purchased Software [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Beginning balance	1,302	1,175
Charge for the year	78	101
Disposals and adjustments	(426)	(7)
Exchange differences	9	33
Ending balance	£ 963	£ 1,302

XML

Intangible Assets - Summary of Intangible Assets (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Amortisation charge related to write off of assets	£ 400
Internally Developed Software [Member]
Disclosure Of Reconciliation Of Changes In Intangible Assets And Goodwill [Line Items]
Amortisation charge related to write off of assets		£ 62

XML

Intangible Assets - Summary of Goodwill Allocated to Cash Generating Units (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Goodwill Allocated To C G Us [Line Items]
Beginning balance	£ 8,042	£ 7,915
Exchange differences	(100)	145
Acquisitions and disposals	11	(18)
Ending balance	7,953	8,042
Consumer [Member]
Disclosure Of Goodwill Allocated To C G Us [Line Items]
Beginning balance	1,183	1,183
Ending balance	1,183	1,183
EE [Member]
Disclosure Of Goodwill Allocated To C G Us [Line Items]
Beginning balance	2,768	4,917
Re-organisation		(2,149)
Ending balance	2,768	2,768
Business and Public Sector [Member]
Disclosure Of Goodwill Allocated To C G Us [Line Items]
Beginning balance	2,570	662
Re-organisation		1,921
Exchange differences	(8)	10
Disposals		(23)
Ending balance	2,562	2,570
Global Services [Member]
Disclosure Of Goodwill Allocated To C G Us [Line Items]
Beginning balance	579	1,153
Re-organisation		(709)
Exchange differences	(92)	135
Acquisitions	11
Ending balance	498	579
Wholesale and Ventures [Member]
Disclosure Of Goodwill Allocated To C G Us [Line Items]
Beginning balance	942
Re-organisation		937
Acquisitions		5
Ending balance	£ 942	£ 942

XML

Intangible Assets - Additional Information (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017
Disclosure of information for cash-generating units [Line Items]
Pre-tax discount rate	8.40%	8.60%
Global Services [Member]
Disclosure of information for cash-generating units [Line Items]
Pre-tax discount rate	8.80%	9.00%
Perpetuity growth rate	2.30%	2.40%
Amount by which unit's recoverable amount exceeds its carrying amount	£ 768	£ 586
Sensitivity analysis, percentage to increase in discount rate	11.50%
Sensitivity analysis of reduction in perpetuity growth rate revised assumption	1.40%
Sensitivity analysis, decrease in cash flows projection	34.00%
Business and Public Sector [Member]
Disclosure of information for cash-generating units [Line Items]
Perpetuity growth rate	2.00%	2.00%
Consumer [Member]
Disclosure of information for cash-generating units [Line Items]
Perpetuity growth rate	2.00%	2.00%
EE [Member]
Disclosure of information for cash-generating units [Line Items]
Perpetuity growth rate	2.00%	2.00%
Wholesale and Ventures [Member]
Disclosure of information for cash-generating units [Line Items]
Perpetuity growth rate	2.00%	2.00%

XML

Property, Plant and Equipment - Summary of the Carrying Values of Software, Property, Plant and Equipment (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance		£ 16,498	£ 15,971
Ending balance		17,000	16,498
Carrying amount before engineering stores		16,956	16,440
Engineering stores		44	58
Carrying amount including engineering stores		17,000	16,498
Gross Carrying Amount [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance		54,025	52,450
Additions	[1]	2,894	2,846
Transfers			4
Disposals and adjustments	[2]	(1,789)	(1,758)
Exchange differences		(53)	483
Ending balance		55,077	54,025
Accumulated Depreciation and Amortisation [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance		(37,585)	(36,550)
Depreciation of property, plant and equipment		2,391	2,392
Disposals and adjustments	[2]	(1,816)	(1,767)
Exchange differences		(39)	410
Ending balance		(38,121)	(37,585)
Land and Buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount before engineering stores	[3]	489	485
Carrying amount including engineering stores	[3]	489	485
Land and Buildings [Member] | Gross Carrying Amount [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance	[3]	1,302	1,278
Additions	[1],[3]	12	6
Transfers	[3]	36	14
Disposals and adjustments	[2],[3]	(82)	(45)
Exchange differences	[3]	(6)	49
Ending balance	[3]	1,262	1,302
Land and Buildings [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance	[3]	(817)	(750)
Depreciation of property, plant and equipment	[3]	57	64
Disposals and adjustments	[2],[3]	(96)	(36)
Exchange differences	[3]	(5)	39
Ending balance	[3]	(773)	(817)
Network Infrastructure [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount before engineering stores	[3]	14,993	14,158
Carrying amount including engineering stores	[3]	14,993	14,158
Network Infrastructure [Member] | Gross Carrying Amount [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance	[3]	49,372	48,194
Additions	[1],[3]	193	40
Transfers	[3]	2,793	2,393
Disposals and adjustments	[2],[3]	(1,540)	(1,637)
Exchange differences	[3]	(35)	382
Ending balance	[3]	50,783	49,372
Network Infrastructure [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance	[3]	(35,214)	(34,287)
Depreciation of property, plant and equipment	[3]	2,213	2,224
Disposals and adjustments	[2],[3]	(1,613)	(1,627)
Exchange differences	[3]	(24)	330
Ending balance	[3]	(35,790)	(35,214)
Land and Buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount before engineering stores	[4]	356	384
Carrying amount including engineering stores	[4]	356	384
Land and Buildings [Member] | Gross Carrying Amount [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance	[4]	1,938	1,870
Additions	[1],[4]	92	128
Transfers	[4]	16	(1)
Disposals and adjustments	[2],[4]	(119)	(106)
Exchange differences	[4]	(13)	47
Ending balance	[4]	1,914	1,938
Land and Buildings [Member] | Accumulated Depreciation and Amortisation [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance	[4]	(1,554)	(1,513)
Depreciation of property, plant and equipment	[4]	121	104
Disposals and adjustments	[2],[4]	(107)	(104)
Exchange differences	[4]	(10)	41
Ending balance	[4]	(1,558)	(1,554)
Assets in Course of Construction [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount before engineering stores		1,118	1,413
Engineering stores		44	58
Carrying amount including engineering stores		1,162	1,471
Assets in Course of Construction [Member] | Gross Carrying Amount [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Opening balance		1,413	1,108
Additions	[1]	2,597	2,672
Transfers		(2,845)	(2,402)
Disposals and adjustments	[2]	(48)	30
Exchange differences		1	5
Ending balance		£ 1,118	£ 1,413

[1] Net of grant funding of £74m (2016/17: £28m net grant deferral).

[2] Fully depreciated assets in the group’s fixed asset registers were reviewed during the year, as part of the group’s annual asset verification exercise, and certain assets that were no longer in use have been written off, reducing cost and accumulated depreciation by £1.3bn (2016/17: £1.1bn).

[3] The carrying amount of the group’s property, plant and equipment includes an amount of £53m (2016/17: £73m) in respect of assets held under finance leases, comprising land and buildings of £42m (2016/17: £45m) and network infrastructure of £11m (2016/17: £28m). The depreciation expense on those assets in 2017/18 was £10m (2016/17: £10m), comprising land and buildings of £3m (2016/17: £3m) and network infrastructure of £7m (2016/17: £7m).

[4] Other mainly comprises motor vehicles, computers and fixtures and fittings.

XML

Property, Plant and Equipment - Summary of the Carrying Values of Software, Property, Plant and Equipment (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount of assets held under finance leases	£ 53	£ 73
Depreciation on assets held under finance leases	10	10
Net grant deferral/funding	74	28
Write off of fully depreciated assets	1,300	1,100
Land and Buildings [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount of assets held under finance leases	42	45
Depreciation on assets held under finance leases	3	3
Network Infrastructure [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Carrying amount of assets held under finance leases	11	28
Depreciation on assets held under finance leases	£ 7	£ 7

XML

Property, Plant and Equipment - Summary of Property, Plant and Equipment (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about property, plant and equipment [Line Items]
Total land and buildings	£ 489	£ 485
Freehold [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Total land and buildings	261	269
Leasehold [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Total land and buildings	£ 228	£ 216

XML

Property, Plant and Equipment - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure of detailed information about property, plant and equipment [Line Items]
Net book value of assets	£ 526	£ 591
Net grant deferral/funding	£ 74	28
Percentage of change in take up assumption rate	4.00%
Movement in deferred grant funding based on change in take up assumption rate	£ 50
Deferred grant funding	£ 536	£ 446
UK [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
BDUK take-up assumption rate	41.00%	39.00%
Network Infrastructure [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Net book value of assets	£ 132	£ 179
Network Infrastructure [Member]
Disclosure of detailed information about property, plant and equipment [Line Items]
Net book value of assets	£ 8,300	£ 8,000
Useful life of assets	more than 18 years

XML

Programme Rights - Summary of Programme Rights (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of detailed information about intangible assets [Line Items]
Beginning balance	£ 264	£ 225
Amortisation	(1,123)	(1,118)	£ (621)
Ending balance	272	264	225
Programme Rights [Member]
Disclosure of detailed information about intangible assets [Line Items]
Beginning balance	264	225
Additions	771	753
Amortisation	(763)	(714)
Ending balance	£ 272	£ 264	£ 225

XML

Inventories - Summary of Inventories (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Classes Of Inventories [Abstract]
Consumables	£ 22	£ 24	£ 26
Work in progress	6	23	11
Finished goods	211	180	152
Inventories	£ 239	£ 227	£ 189

XML

Inventories - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Classes Of Inventories [Abstract]
Inventories expenses	£ 2,588	£ 2,680

XML

Trade and Other Receivables - Schedule of Trade and Other Receivables (Detail) - GBP (£) £ in Millions		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Non-current
Other assets	[1]	£ 317	£ 360	£ 218
Current
Trade receivables		1,741	1,774	1,803
Amounts owed by ultimate parent company		15	25	9
Prepayments	[2]	1,103	733	702
Accrued income		777	955	1,072
Other receivables	[3]	393	373	401
Trade and other receivable current		£ 4,029	£ 3,860	£ 3,987

[1] Other assets includes costs relating to the initial set-up, transition or transformation phase of long-term networked IT services contracts of £145m (2016/17: £163m, 2015/16: £111m), and prepayments and leasing debtors of £172m (2016/17: £197m, 2015/16: £107m).

[2] Prepayments includes £325m (2016/17: £nil, 2015/16: £nil) in respect of the acquisition of spectrum in April 2018. The spectrum auction bidding cut across the 2017/18 and 2018/19 financial years. Whilst £325m was on deposit with Ofcom at 31 March 2018, we went on to win spectrum for a total price of £304m and the excess deposit balance has since been refunded. This will be transferred to intangible assets in 2018/19.

[3] Other receivables includes assets held for sale of £nil (2016/17: £22m, 2015/16: £nil).

XML

Trade and Other Receivables - Schedule of Trade and Other Receivables (Parenthetical) (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of Trade and Other Receivables [line items]
Other assets relating to initial set-up, transition or transformation phase of long-term networked IT services contracts		£ 145	£ 163	£ 111
Other assets relating to prepayments and leasing debtors		172	197	107
Other receivables	[1]	393	373	401
Spectrum [Member]
Disclosure of Trade and Other Receivables [line items]
Prepayments in respect of acquisition		325	0	0
Cash transferred in respect of acquisition		304
Current Assets Held for Sale [Member]
Disclosure of Trade and Other Receivables [line items]
Other receivables		£ 0	£ 22	£ 0

[1] Other receivables includes assets held for sale of £nil (2016/17: £22m, 2015/16: £nil).

XML

Trade and Other Receivables - Summary of Trade Receivables After Deducting Allowances for Doubtful Debts (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Trade And Other Receivables [Abstract]
At 1 April	£ 303	£ 195	£ 196
Expense	129	211	77
Utilised	(61)	(114)	(89)
Exchange differences	4	11	11
At 31 March	£ 375	£ 303	£ 195

XML

Trade and Other Receivables - Summary of Trade Receivables Past Due and Not Specifically Impaired (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of Trade and Other Receivables [line items]
Trade receivables	£ 1,741	£ 1,774	£ 1,803
Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables	1,251	1,184	1,152
Current [Member] | Trade Receivables Specifically Impaired Net of Provision [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables	61	146	98
Between 0 and 3 Months [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables	293	292	368
Between 3 and 6 Months [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables	44	17	51
Between 6 and 12 Months [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables	25	41	44
Over 12 Months [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables	£ 67	£ 94	£ 90

XML

Trade and Other Receivables - Additional Information (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of Trade and Other Receivables [line items]
Cash collateral held against trade and other receivables	£ 6	£ 4	£ 4
Gross Trade Receivables Specifically Impaired [Member]
Disclosure of Trade and Other Receivables [line items]
Gross trade receivables specifically impaired	£ 124	£ 238	£ 192

XML

Trade and Other Receivables - Schedule of Trade Receivables Not Past Due and Accrued Income (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of Trade and Other Receivables [line items]
Accrued income	£ 777	£ 955	£ 1,072
Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	1,251	1,184	1,152
BT Consumer [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	86	90	83
BT Consumer [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	157	128	138
EE [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	122	170	312
EE [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	206	335	267
Business and Public Sector [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	134	151	146
Business and Public Sector [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	253	200	115
Global Services [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	222	297	351
Global Services [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	477	444	555
Wholesale and Ventures [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	145	167	99
Wholesale and Ventures [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	92	75	76
Openreach [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	67	78	79
Openreach [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	61	1	1
Other [Member]
Disclosure of Trade and Other Receivables [line items]
Accrued income	1	2	£ 2
Other [Member] | Current [Member]
Disclosure of Trade and Other Receivables [line items]
Trade receivables not past due	£ 5	£ 1

XML

Trade and Other Payables - Summary of Trade and Other Payables (Detail) - GBP (£) £ in Millions		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Current
Trade payables		£ 3,991	£ 4,205	£ 4,331
Amounts owed to parent company		50	63	70
Other taxation and social security		704	704	682
Other payables		428	648	527
Accrued expenses		492	382	418
Deferred income	[1]	1,525	1,474	1,435
Total current trade and other payables		7,190	7,476	7,463
Non-current
Other payables	[2]	871	885	876
Deferred income	[1]	455	413	230
Total non-current trade and other payables		£ 1,326	£ 1,298	£ 1,106

[1] Includes £132m (2016/17: £71m, 2015/16: £71m) current and £404m (2016/17: £375m, 2015/16: £187m) non-current liabilities relating to the Broadband Delivery UK programme, for which grants received by the group may be subject to re-investment or repayment depending on the level of take-up

[2] Other payables relate to operating lease liabilities and deferred gains on a 2001 sale and finance leaseback transaction.

XML

Trade and Other Payables - Summary of Trade and Other Payables (Parenthetical) (Detail) - GBP (£) £ in Millions		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Trade And Other Payables [Line Items]
Deferred income current	[1]	£ 1,525	£ 1,474	£ 1,435
Deferred income non-current	[1]	455	413	230
Broadband Delivery UK Programme [Member]
Disclosure Of Trade And Other Payables [Line Items]
Deferred income current		132	71	71
Deferred income non-current		£ 404	£ 375	£ 187

[1] Includes £132m (2016/17: £71m, 2015/16: £71m) current and £404m (2016/17: £375m, 2015/16: £187m) non-current liabilities relating to the Broadband Delivery UK programme, for which grants received by the group may be subject to re-investment or repayment depending on the level of take-up

XML

Provisions - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of other provisions [Line Items]
Additional provisions	£ 133	£ 536
Trade and other payables	7,190	7,476	£ 7,463
Internal cost	20,339	20,892	£ 15,397
Contract loss provisions	38	29
Regulatory [Member]
Disclosure of other provisions [Line Items]
Additional provisions	51	426
Fine [Member]
Disclosure of other provisions [Line Items]
Trade and other payables		42
Network Share Provision [Member]
Disclosure of other provisions [Line Items]
Additional provisions		5
Specific Item [Member]
Disclosure of other provisions [Line Items]
Additional provisions	£ 51	126
Specific Item [Member] | Regulatory [Member]
Disclosure of other provisions [Line Items]
Additional provisions		300
Specific Item [Member] | Provision [Member]
Disclosure of other provisions [Line Items]
Internal cost		£ 342
Top of Range [Member] | Network Share Provision [Member]
Disclosure of other provisions [Line Items]
Number of years for which costs are expected to be incurred	20 years

XML

Provisions - Details of Estimate of the Provisions (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of other provisions [Line Items]
Opening balance	£ 1,161	£ 743
Income statement expense	133	536
Unwind of discount	15	16	£ 8
Utilised or released	(336)	(135)
Transfers	85	(3)
Exchange differences	(3)	4
Ending balance	1,055	1,161	743
Restructuring Provision [Member]
Disclosure of other provisions [Line Items]
Opening balance	11	20
Income statement expense	4
Utilised or released	(2)	(10)
Exchange differences	(1)	1
Ending balance	12	11	20
Property, plant and equipment [member]
Disclosure of other provisions [Line Items]
Opening balance	292	296
Income statement expense	37	38
Unwind of discount	11	12
Utilised or released	(46)	(54)
Ending balance	294	292	296
Network ARO Provision [Member]
Disclosure of other provisions [Line Items]
Opening balance	83	78
Income statement expense	2	27
Unwind of discount	2	2
Utilised or released	(16)	(24)
Ending balance	71	83	78
Network Share Provision [Member]
Disclosure of other provisions [Line Items]
Opening balance	50	60
Income statement expense		5
Unwind of discount	2	2
Utilised or released	(19)	(17)
Ending balance	33	50	60
Regulatory [Member]
Disclosure of other provisions [Line Items]
Opening balance	479	64
Income statement expense	51	426
Utilised or released	(210)	(11)
Ending balance	320	479	64
Litigation [Member]
Disclosure of other provisions [Line Items]
Opening balance	69	73
Income statement expense	6	6
Utilised or released	(11)	(11)
Exchange differences		1
Ending balance	64	69	73
Other [Member]
Disclosure of other provisions [Line Items]
Opening balance	177	152
Income statement expense	33	34
Utilised or released	(32)	(8)
Transfers	85	(3)
Exchange differences	(2)	2
Ending balance	£ 261	£ 177	£ 152

XML

Provisions - Details of Provisions (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Other Provisions [Abstract]
Current	£ 603	£ 625	£ 178
Non-current	452	536	565
Total	£ 1,055	£ 1,161	£ 743

XML

Retirement Benefit Plans - Additional Information (Detail) £ in Thousands		1 Months Ended			12 Months Ended				36 Months Ended
	Apr. 01, 2009	Dec. 31, 2017 Employee	Jun. 30, 2017 GBP (£)	Jun. 30, 2014 GBP (£)	Mar. 31, 2019 GBP (£)	Mar. 31, 2018 GBP (£) Member Valuation	Mar. 31, 2017 GBP (£)	Mar. 31, 2016 GBP (£)	Jun. 30, 2017 GBP (£)
Disclosure Of Retirement Benefit Plans [Line Items]
Transition payments percentage						2.00%
Weighted average term of liabilities						16 years
Length of time over which payments will be made to all retirees from the fund						70 years
Normal pensionable age	60 years
Maximum period of addressing deficit						20 years
Number of recent triennial valuations | Valuation						2
Percentage of investment in growth asset			45.00%	60.00%					45.00%
De-risking to low risk investment approach year			2034	2034
Flat discount rate			1.00%						1.00%
Threshold dividend per share						10.00%
Threshold dividend per share of share buybacks						£ 200,000
Share buybacks in excess per year						200,000
Threshold for BTPS						1,500,000
Deficit threshold level for application for provision						£ 2,000,000
BTRSS [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Number of active members | Member						35,000
Contribution to plan						£ 167,000
Each Month Between 1 April 2018 and November 2020
Disclosure Of Retirement Benefit Plans [Line Items]
Monthly payments to bridge funding deficit						1,875
Group Contribution
Disclosure Of Retirement Benefit Plans [Line Items]
Group contributions based on funding valuation agreement					£ 2,075,000
Top of Range [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Prudent discount rate			1.40%						1.40%
Proceeds from disposals net of acquisitions			£ 1,000,000			1,000,000
Bottom of Range [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Prudent discount rate			0.70%						0.70%
Trade and Other Payables [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Present value of liabilities						£ 17,000	£ 15,000	£ 15,000
BT Pension Scheme [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Percentage of future benefit accrual						99.00%
Number of members in pension scheme | Member						293,000
BT Retirement Saving Scheme [Mmeber]
Disclosure Of Retirement Benefit Plans [Line Items]
Contribution rate						10.00%
BT Retirement Saving Scheme [Mmeber] | Top of Range [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Contribution rate						11.00%
BTPS [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Normal pensionable age	65 years
Percentage of group's retirement benefit obligation						97.00%
Percentage retirement benefit obligation are rounded						0.05%
Percentage of exposure covered by longevity insurance						25.00%
Funding deficit contribution			£ 2,000,000						£ 2,000,000
Asset return percentage									10.50%
Funding deficit			£ 11,300,000	£ 7,000,000					£ 11,300,000
Recovery period			13 years
Payments under recovery plan						£ 850,000
Fixed interest on bonds						1,000
CPI Linked Bonds						£ 1,000
Annual payment term						10 years
Annual payment maturity range start						2020-04
Annual payment maturity range end						2030-03
Annual payment amount						£ 900,000
Deficit contributions						850,000	£ 250,000
BTPS [Member] | Financial Year 2020/2021 [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Deficit contributions						£ 400,000
Deficit contributions payment date						2020-06
BTPS [Member] | Due in 30 June 2020 [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Material contributions included in recovery plan						£ 4,500,000
BTPS [Member] | Issuance of Bond [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Proceeds from issuance of bond					£ 2,000,000
BTPS [Member] | Over Three Years to 31 March 2020 [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Payments under recovery plan						2,100,000
BTPS [Member] | Over Two Years to 30 June 2019 [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Payments under recovery plan						£ 1,250,000
BTPS [Member] | Top of Range [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Bond maturity term						2042
BTPS [Member] | Bottom of Range [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Bond maturity term						2033
Ordinary Contributions [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Group contributions based on funding valuation agreement						£ 75,000
Deficit Contributions [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Group contributions based on funding valuation agreement						2,000,000
EEPS [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Funding deficit						141,000
Defined benefit liabilities						£ 900,000
Number of active members | Member						11,500
EE Pension Scheme [Member] | Global Equities [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Percentage of assets of benefit plan						28.00%
EE Pension Scheme [Member] | Property and Illiquid Alternatives [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Percentage of assets of benefit plan						22.00%
EE Pension Scheme [Member] | Absolute Return Portfolio [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Percentage of assets of benefit plan						25.00%
EE Pension Scheme [Member] | Liability Driven Investment Portfolio [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Percentage of assets of benefit plan						25.00%
Other Pension Plans [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Number of defined benefit plans closed | Employee		2
Contribution to plan						£ 14,000
Other Pension Plans [Member] | Foreign Country [Member]
Disclosure Of Retirement Benefit Plans [Line Items]
Contribution to plan						£ 3,000

XML

Retirement Benefit Plan - Summary of Retirement Benefit Plan (Detail)	12 Months Ended
	Mar. 31, 2018
Defined Contribution Plans [Member]
Disclosure Of Defined Benefit Plans [Line Items]
What are they?	Benefits in a defined contribution plan are linked to: – contributions paid – the performance of each individual’s chosen investments – the form in which individuals choose to take their benefits. Contributions are paid into an independently administered fund.
How do they impact BT’s financial statements?	The income statement charge in respect of defined contribution plans represents the contribution payable by the group based upon a fixed percentage of employees’ pay. The group has no exposure to investment and other experience risks.
Defined Benefit Plan [Member]
Disclosure Of Defined Benefit Plans [Line Items]
What are they?	Benefits in a defined benefit plan are: – determined by the plan rules, dependent on factors such as age, years of service and pensionable pay – not dependent upon actual contributions made by the company or members.
How do they impact BT’s financial statements?	The income statement service cost in respect of defined benefit plans represents the increase in the defined benefit liability arising from pension benefits earned by active members in the current period. The group is exposed to investment and other experience risks and may need to make additional contributions where it is estimated that the benefits will not be met from regular contributions, expected investment income and assets held.

XML

Retirement Benefit Plan - Summary of Expense or Income from Retirement Benefit Arrangements Recognised in Income Statement (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Service cost (including administration expenses & PPF levy):
Service cost (including administration expenses & PPF levy)	£ 624	£ 521	£ 494
Net interest expense on pensions deficit included in specific items (note 8)	218	209	221
Total recognised in the income statement	842	730	715
Defined Benefit Plan [Member]
Service cost (including administration expenses & PPF levy):
Service cost (including administration expenses & PPF levy)	376	281	301
Defined Contribution Plans [Member]
Service cost (including administration expenses & PPF levy):
Service cost (including administration expenses & PPF levy)	265	£ 240	£ 193
Past Service Credit [Member]
Service cost (including administration expenses & PPF levy):
Service cost (including administration expenses & PPF levy)	£ (17)

XML

Retirement Benefit Plan - Summary of Pension Obligation in Respect of Defined Benefit Plans Reported in Balance Sheet (Parenthetical) (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Unfunded Pension Arrangements [Member] | Other Plans [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Present value of liabilities	£ 97	£ 104	£ 104

XML

Retirement Benefit Plan - Summary of Pension Obligation in Respect of Defined Benefit Plans Reported in Balance Sheet (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Defined Benefit Plans [Line Items]
Deficit	£ (5,290)	£ (7,553)
Retirement Benefit Obligation Before Adjustments [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assets	50,956	51,112
Present value of liabilities	(57,327)	(60,200)
Deficit	(6,371)	(9,088)
Retirement Benefit Obligation Before Adjustments [Member] | BT Pension Scheme [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assets	49,894	50,090
Present value of liabilities	(55,783)	(58,649)
Deficit	(5,889)	(8,559)
Retirement Benefit Obligation Before Adjustments [Member] | EE Pension Scheme [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assets	763	748
Present value of liabilities	(920)	(973)
Deficit	(157)	(225)
Retirement Benefit Obligation Before Adjustments [Member] | Other Pension Plans [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assets	299	274
Present value of liabilities	(624)	(578)
Deficit	(325)	(304)
Deferred Tax Asset [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Deficit	£ 1,081	£ 1,535

XML

Retirement Benefit Plan - Summary of Movements on Pension Assets and Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Defined Benefit Plans [Line Items]
Service cost (including administration expenses and PPF levy)	£ (624)	£ (521)	£ (494)
Interest on pension deficit	(218)	(209)	(221)
Assets [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Beginning balance	50,956	51,112	43,968
Service cost (including administration expenses and PPF levy)	(67)	(44)
Interest on pension deficit	1,201	1,413
Return on plan assets above the amount included in the group income statement	10	7,475
Regular contributions by employer	264	313
Deficit contributions by employer	872	274
Contributions by employees	2	8
Benefits paid	(2,449)	(2,315)
Foreign exchange	11	20
Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Beginning balance	(57,327)	(60,200)	(50,350)
Service cost (including administration expenses and PPF levy)	(309)	(237)
Interest on pension deficit	(1,419)	(1,622)
Actuarial loss arising from changes in financial assumptions	2,251	(10,221)
Actuarial loss arising from changes in demographic assumptions	(221)	(206)
Actuarial gain arising from experience adjustments	120	163
Contributions by employees	(2)	(8)
Benefits paid	2,449	2,315
Foreign exchange	(13)	(34)
Past service credit	17
Deficit [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Beginning balance	(6,371)	(9,088)	£ (6,382)
Service cost (including administration expenses and PPF levy)	(376)	(281)
Interest on pension deficit	(218)	(209)
Included in the group income statement	(577)	(490)
Return on plan assets above the amount included in the group income statement	10	7,475
Actuarial loss arising from changes in financial assumptions	2,251	(10,221)
Actuarial loss arising from changes in demographic assumptions	(221)	(206)
Actuarial gain arising from experience adjustments	120	163
Included in the group statement of comprehensive income	2,160	(2,789)
Regular contributions by employer	264	313
Deficit contributions by employer	872	274
Included in the group cash flow statement	1,136	587
Foreign exchange	(2)	(14)
Other movements	(2)	£ (14)
Past service credit	£ 17

XML

Retirement Benefit Plan - Summary of Analysis of Membership (Detail) - BT Pension Scheme [Member] £ in Billions	Mar. 31, 2018 GBP (£) Member
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 55.8
Total number of members | Member	293,000
IAS 19 Sections A and B Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 38.8
IAS 19 Section C Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	17.0
Active [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 12.6
Total number of members | Member	30,000
Active [Member] | IAS 19 Sections A and B Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 4.9
Active [Member] | IAS 19 Section C Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	7.7
Deferred Members [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 10.0
Total number of members | Member	60,500
Deferred Members [Member] | IAS 19 Sections A and B Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 4.3
Deferred Members [Member] | IAS 19 Section C Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	5.7
Pensioners [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 33.2
Total number of members | Member	202,500
Pensioners [Member] | IAS 19 Sections A and B Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 29.6
Pensioners [Member] | IAS 19 Section C Liabilities [Member]
Disclosure Of Defined Benefit Plans [Line Items]
IAS 19 liabilities (bn)	£ 3.6

XML

Retirement Benefit Plan - Summary of Fair Value of Assets of BTPS Analysed by Asset Category (Detail) - At Fair Value [Member] - BT Pension Scheme [Member] - GBP (£) £ in Billions		Mar. 31, 2018		Mar. 31, 2017
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 49.9		£ 50.1
of which quoted £bn	[1]	£ 29.7		£ 28.3	[2]
Total	[1]	100.00%	[2]	100.00%
Private Equity [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 1.9		£ 1.9
Total	[1]	4.00%	[2]	4.00%
UK Equity [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 0.5		£ 0.7
of which quoted £bn	[1]	£ 0.5		£ 0.6	[2]
Total	[1]	1.00%	[2]	2.00%
Overseas Developed Equity [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 7.8		£ 9.1
of which quoted £bn	[1]	£ 7.3		£ 8.6	[2]
Total	[1]	16.00%	[2]	18.00%
Emerging Markets Equity [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 0.5		£ 0.5
of which quoted £bn	[1]	£ 0.4		£ 0.1	[2]
Total	[1]	1.00%	[2]	1.00%
UK Property [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 3.9		£ 4.1
Total	[1]	8.00%	[2]	8.00%
Overseas Property [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 1.2		£ 1.7
Total	[1]	2.00%	[2]	3.00%
Absolute Return [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1],[3]	£ 1.5		£ 2.3
Total	[1],[3]	3.00%	[2]	5.00%
Non Core Credit [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1],[4]	£ 3.4		£ 3.5
of which quoted £bn	[1],[4]	£ 1.0		£ 1.1	[2]
Total	[1],[4]	7.00%	[2]	7.00%
Mature Infrastructure [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 1.4		£ 1.7
Total	[1]	3.00%	[2]	3.00%
UK Index Linked Government Bonds [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 12.5		£ 12.3
of which quoted £bn	[1]	£ 12.5		£ 12.0	[2]
Total	[1]	25.00%	[2]	25.00%
Global Investment Grade Credit [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 10.0		£ 7.6
of which quoted £bn	[1]	£ 8.0		£ 5.9	[2]
Total	[1]	20.00%	[2]	15.00%
Cash Balances [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1]	£ 3.8		£ 1.7
Total	[1]	7.00%	[2]	3.00%
Longevity Insurance Contract [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1],[5]	£ (0.4)		£ (0.3)
Total	[1],[5]	(1.00%)	[2]	(1.00%)
Other Non-physical Cash [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Total assets £bn	[1],[6]	£ 1.9		£ 3.3
Total	[1],[6]	4.00%	[2]	7.00%

[1] a At 31 March 2018, the Scheme’s assets included equity issued by the group of £3m (2016/17: £nil) . The Scheme also held £10m (2016/17: £10m) of index-linked bonds issued by the group.

[2] Assets with a quoted price in an active market.

[3] This allocation seeks to generate returns irrespective of the direction of markets. Managers within this allocation will typically manage their portfoilios without close regard to a specific market benchmark.

[4] This allocation includes a range of credit investments, including emerging market, sub-investment grade and unrated credit. The allocation seeks to exploit investment opportunities within credit markets using the expertise of a range of specialist investment managers.

[5] The Trustee has hedged some of the Scheme’s longevity risk through a longevity insurance contract which was entered into in 2014. The value reflects experience to date on the contract from higher than expected deaths. This amount partly offsets a reduction recognised in the Scheme’s liabilities.

[6] Non-physical cash includes offsets in future positions and cash collateral posted in relation to derivatives held by the Scheme.

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Retirement Benefit Plan - Summary of Fair Value of Assets of BTPS Analysed by Asset Category (Parenthetical) (Detail) - BT Pension Scheme [Member] - GBP (£)	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Defined Benefit Plans [Line Items]
Ordinary shares held under scheme	£ 3,000,000	£ 0
Index-linked bonds held under scheme	£ 10,000,000	£ 10,000,000

XML

Retirement Benefit Plan - Summary of Approach Used to Set the Key IAS 19 Assumptions (Detail) - BT Pension Scheme [Member]	12 Months Ended
	Mar. 31, 2018
Actuarial Assumption of Discount Rates [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Approach used to set key IAS 19 assumptions	IAS 19 requires that the discount rate is determined by reference to market yields at the reporting date on high quality corporate bonds. The currency and term of these should be consistent with the currency and estimated term of the pension obligations. The assumption is calculated by applying the projected BTPS benefit cash flows to a corporate bond yield curve constructed based on the yield on AA-rated corporate bonds. In setting the yield curve, judgement is required on the selection of appropriate bonds to be included in the universe and the approach used to then derive the yield curve. At 31 March 2018, the discount rate model used to select bonds and derive the yield curve was updated to better reflect yields on corporate bonds over the life of the Scheme. A key difference is that the revised model excludes bonds which have either an implicit or explicit Government guarantee, which is more consistent with the requirements of IAS19, and reflects developing practice. Both the old and revised models are standard models developed by our external actuary. The impact of this change is a £2.1bn reduction in the BTPS liabilities.
Actuarial Assumption of Expected Rates Off Retail Prices Index Inflation [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Approach used to set key IAS 19 assumptions	The RPI inflation assumption is set using the entire inflation curve, weighted by projected BTPS benefit cash flows, and making an adjustment for an inflation risk premium (to reflect the extra premium paid by investors for inflation protection), which is currently assumed to be 20bps.
Actuarial Assumption of Expected Rates of Consumer Prices Index Inflation [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Approach used to set key IAS 19 assumptions	CPI is assessed at a margin below RPI taking into account market forecasts and independent estimates of the expected difference.
Actuarial Assumption of Expected Rates of Salary Increases [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Approach used to set key IAS 19 assumptions	Long-term salary increases for BTPS members are assumed to be equal to CPI inflation.
Actuarial Assumption of Expected Rates of Pension Increases [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Approach used to set key IAS 19 assumptions	Benefits are assumed to increase in line with the RPI or CPI inflation assumptions, based on the relevant index for increasing benefits, as prescribed by the rules of the BTPS and summarised above.
Actuarial Assumption of Mortality Rates [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Approach used to set key IAS 19 assumptions	The longevity assumption has been updated to take into account: – the actual mortality experience of the BTPS pensioners, based on a formal review conducted at the 2014 triennial funding valuation – future improvements in longevity based on a model published by UK actuarial profession’s Continuous Mortality Investigation (using the CMI 2016 Mortality Projections model with a 1.25% per year long-term improvement parameter).

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Retirement Benefit Plan - Summary of Approach Used to Set the Key IAS 19 Assumptions (Parenthetical) (Detail) £ in Billions	12 Months Ended
	Mar. 31, 2018 GBP (£)
Disclosure Of Defined Benefit Plans [Line Items]
Mortality Projections model, long-term improvement parameter, per year	1.25%
BT Pension Scheme [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Reduction in liabilities	£ 2.1

XML

Retirement Benefit Plan - Summary of Key Financial Assumptions Used to Measure Liabilities of BTPS (Detail)	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Real Rates [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Rate used to discount liabilities	(0.44%)	(0.78%)	0.44%
Real Rates [Member] | Consumer Price Index [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Inflation – increase	(1.10%)	(1.20%)	(1.20%)
Nominal Rates [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Rate used to discount liabilities	2.65%	2.40%	3.30%
Nominal Rates [Member] | Retail Price Index [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Inflation – increase	3.10%	3.20%	2.85%
Nominal Rates [Member] | Consumer Price Index [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Inflation – increase	2.00%	2.00%	1.65%

XML

Retirement Benefit Plan - Summary of Key Financial Assumptions Used to Measure Liabilities of BTPS (Parenthetical) (Detail)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Defined Benefit Plans [Abstract]
Maximum assumed real rate	0.10%	0.50%	0.20%

XML

Retirement Benefit Plan - Summary of Forecast Life Expectancies for BTPS Members Aged 60 (Detail) - yr	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2014
Male in Lower Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of years	25.8	25.9	26.2	26.1
Male in Medium Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of years	27.1	27.2	27.5	27.5
Male in Higher Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of years	28.5	28.6	28.9	29.0
Female in Lower Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of years	28.5	28.6	28.9	28.9
Female in Higher Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of years	28.7	28.9	29.2	29.2
Average Improvement for a Member Retiring at Age 60 in 10 Years Time [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of years	0.7	0.9	1.0	1.3

XML

Retirement Benefit Plans - Summary of Assessed Potential Negative Impact of Key Risk (Detail)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Defined Benefit Plans [Abstract]
Fall in discount rate	1.10%	1.00%
Increase to inflation rate	0.70%	0.90%
Increase to life expectancy	1 year 4 months 6 days	1 year 4 months 6 days

XML

Retirement Benefit Plan - Summary of Two Most Recent Triennial Valuations (Detail) - BTPS [Member] - GBP (£) £ in Billions	Jun. 30, 2017	Jun. 30, 2014
Disclosure Of Defined Benefit Plans [Line Items]
BTPS liabilities	£ (60.4)	£ (47.2)
Market value of BTPS assets	49.1	40.2
Funding deficit	£ (11.3)	£ (7.0)
Percentage of accrued benefits covered by BTPS assets at the valuation date	81.30%	85.20%
Percentage of accrued benefits on a solvency basis covered by the BTPS assets at the valuation date	62.20%	63.00%

XML

Retirement Benefit Plan - Summary of Prudent Long-Term Assumptions (Detail)	Jun. 30, 2017	Jun. 30, 2014
Nominal Rates [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Average single equivalent discount rate	2.60%	4.50%
Average long-term increase in RPI	3.40%	3.50%
Average long-term increase in CPI	2.40%	2.50%
Real Rates [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Average single equivalent discount rate	(0.80%)	1.00%
Average long-term increase in CPI	(1.00%)	(1.00%)

XML

Retirement Benefit Plan - Summary of Average Life Expectancies for Members Aged 60 (Detail) - yr	Mar. 31, 2018	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2014
Male in Lower Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assumptions	25.8	25.9	26.2	26.1
Male in Medium Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assumptions	27.1	27.2	27.5	27.5
Male in Higher Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assumptions	28.5	28.6	28.9	29.0
Female in Lower Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assumptions	28.5	28.6	28.9	28.9
Female in Higher Pay Bracket [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assumptions	28.7	28.9	29.2	29.2
Average Improvement for a Member Retiring at Age 60 in 10 Years Time [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Assumptions	0.7	0.9	1.0	1.3

XML

Retirement Benefit Plan - Summary of Payments Made to BTPS (Detail) - BTPS [Member] - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Defined Benefit Plans [Line Items]
Ordinary contributions	£ 248	£ 303
Deficit contributions	850	250
Total contributions in the year	£ 1,098	£ 553

XML

Retirement Benefit Plans - Schedule of Future Deficit Payments to BTPS (Detail) £ in Millions	12 Months Ended
	Mar. 31, 2018 GBP (£)
2018 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	£ 850
2019 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	2,000
2020 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	1,250
2021 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	900
2022 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	900
2023 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2024 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2025 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2026 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2027 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2028 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2029 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	907
2030 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution (£m)	£ 907

XML

Retirement Benefit Plans - Schedule of Future Deficit Payments to BTPS (Parenthetical) (Detail) £ in Millions	12 Months Ended
	Mar. 31, 2018 GBP (£)
2020 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution payable amount	£ 400
2021 [Member]
Disclosure of defined benefit plans [Line Items]
Deficit contribution payable amount	£ 200

XML

Share-Based Payments - Summary of Plans and Analysis of Total Charge by Type of Award (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share/Save Plans	£ 84	£ 57	£ 58
Employee Saveshare Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share/Save Plans	42	40	27
Incentive Share Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share/Save Plans	16		21
Deferred Bonus Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share/Save Plans	4	9	4
Retention Share Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share/Save Plans	21	£ 8	1
Other Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share/Save Plans	£ 1		£ 5

XML

Share-Based Payments - Additional Information (Detail)	12 Months Ended
	Mar. 31, 2018 GBP (£) yr	Mar. 31, 2017 GBP (£)	Mar. 31, 2016 GBP (£)
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share-based arrangements, term (in years) | yr	3
Share-based awards, awards grant date	in 2017/18, 2016/17 and 2015/16
Percentage of each award linked to total shareholder return	40.00%
Percentage of each award linked to three-year cumulative free cash flow measure	40.00%
Percentage of growth in underlying revenue excluding transit	20.00%
Cumulative period for free cash flow measure	3 years
Weighted average share price	£ 3.11	£ 3.57	£ 4.63
Options pricing model	Binomial options pricing model
Options pricing model, valuation method	Monte Carlo simulations
Share-based awards, performance period	three-year
Share-based awards, expected life after vesting date	3 months
Employee Saveshare Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Savings-related share option plan saving period basis	Monthly
Share-based awards, term	Over a three or five-year period
Share-based awards, exercise period	6 months
Weighted average share price	£ 2.96	4.22	4.54
Employee Saveshare Plans [Member] | Bottom of Range [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share-based arrangements, term (in years) | yr	3
Employee Saveshare Plans [Member] | Top of Range [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Share-based arrangements, term (in years) | yr	5
Employee Saveshare Plans [Member] | Five Year Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Percentage of discount set to market price	20.00%
Employee Saveshare Plans [Member] | Three Year Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Percentage of discount set to market price	10.00%
Deferred Bonus Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average share price	£ 2.82	4.21	4.51
Retention Share Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average share price	£ 2.82	£ 4.17	£ 4.20

XML

Share-Based Payments - Summary of Movements in Employee Saveshare Options - Movement in Number of Share Options(Detail) - Option Option in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Outstanding at 31 March	175
Employee Saveshare Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Outstanding at 1 April	189	197	226
Granted	69	44	47
Forfeited	(41)	(18)	(12)
Exercised	(30)	(33)	(63)
Expired	(12)	(1)	(1)
Outstanding at 31 March	175	189	197

XML

Share-Based Payments - Summary of Movements in Employee Saveshare Options - Weighted Average Share Price (Detail) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Outstanding at 31 March	£ 3.06
Employee Saveshare Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Outstanding at 1 April	3.13	£ 2.87	£ 2.26
Granted	2.50	3.62	3.85
Forfeited	3.28	3.45	3.06
Exercised	1.69	2.08	1.39
Expired	3.53	3.45	2.47
Outstanding at 31 March	3.06	3.13	2.87
Exercisable at 31 March	£ 3.20	£ 2.37	£ 1.40

XML

Share-Based Payments - Summarises Information Relating to Options Outstanding and Exercisable Under Employee Saveshare Plans (Detail) Option in Millions	Mar. 31, 2018 GBP (£) Option mo
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average exercise price	£ 3.06
Number of outstanding options | Option	175
Weighted average remaining contractual life | mo	33
2018 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average exercise price	£ 3.06
Number of outstanding options | Option	25
Weighted average remaining contractual life | mo	10
2018 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average exercise price	£ 3.33
Number of outstanding options | Option	53
Weighted average remaining contractual life | mo	22
2019 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average exercise price	£ 3.07
Number of outstanding options | Option	44
Weighted average remaining contractual life | mo	34
2020 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average exercise price	£ 3.53
Number of outstanding options | Option	17
Weighted average remaining contractual life | mo	46
2021 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average exercise price	£ 2.43
Number of outstanding options | Option	36
Weighted average remaining contractual life | mo	58
Bottom of Range [Member] | 2018 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	£ 2.49
Bottom of Range [Member] | 2018 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	3.19
Bottom of Range [Member] | 2019 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	2.43
Top of Range [Member] | 2018 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	4.23
Top of Range [Member] | 2018 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	3.97
Top of Range [Member] | 2019 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	3.76
Top of Range [Member] | 2020 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	3.53
Top of Range [Member] | 2021 [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Exercise price per share	£ 2.43

XML

Share-Based Payments - Summary of Movements in Executive Share Plan Awards (Detail) shares in Millions, Instrument in Millions	12 Months Ended
	Mar. 31, 2018 Instrument shares
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
At 1 April 2017	56
Awards granted	38
Awards vested	(5)
Awards lapsed	(21)
Dividend shares reinvested | shares	4
At 31 March 2018	72
Incentive Share Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
At 1 April 2017	45
Awards granted	26
Awards lapsed	(20)
Dividend shares reinvested | shares	3
At 31 March 2018	54
Deferred Bonus Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
At 1 April 2017	7
Awards granted	2
Awards vested	(3)
At 31 March 2018	6
Retention Share Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
At 1 April 2017	4
Awards granted	10
Awards vested	(2)
Awards lapsed	(1)
Dividend shares reinvested | shares	1
At 31 March 2018	12

XML

Share-Based Payments - Summary of Fair Values and Key Assumptions Used for Valuing Grants Made Under Employee Saveshare Plans and ISP (Detail) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average share price	£ 3.11	£ 3.57	£ 4.63
Employee Saveshare Plans [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average fair value	0.56	0.72	0.81
Weighted average share price	2.96	4.22	4.54
Weighted average exercise price	£ 250	£ 362	£ 385
Employee Saveshare Plans [Member] | Bottom of Range [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Expected dividend yield	3.12%	2.90%	3.20%
Risk free rates	0.10%	0.50%	0.70%
Expected volatility	23.10%	19.00%	19.70%
Employee Saveshare Plans [Member] | Top of Range [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Expected dividend yield	3.21%	3.40%	3.70%
Risk free rates	0.20%	0.80%	1.60%
Expected volatility	24.30%	21.50%	22.70%
Incentive Share Plan [Member]
Disclosure of terms and conditions of share-based payment arrangement [Line Items]
Weighted average fair value	£ 2.02	£ 3.28	£ 3.64
Weighted average share price	£ 2.81	£ 4.26	£ 4.51
Risk free rates	0.20%	0.60%	0.70%
Expected volatility	23.60%	21.80%	22.00%

XML

Investments - Summary of Investments (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Non-current assets
Available-for-sale	£ 46	£ 37	£ 39
Non-current assets	13,354	11,606	11,965
Fair value through profit or loss	7	7	7
Current assets
Available-for-sale	2,575	1,437	2,878
Current assets	3,224	1,740	3,271
Loans and receivables	447	83	40
Ultimate Parent Company [Member]
Non-current assets
Non-current assets	2,983	1,371	1,409
Current assets
Current assets	34	28	26
British Telecommunications plc [Member]
Non-current assets
Non-current assets	10,318	10,191	10,510
Current assets
Current assets	£ 168	£ 192	£ 327

XML

Investments - Additional Information (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of investment [line items]
Available-for-sale investments	£ 2,621	£ 1,474	£ 2,917
Level 2 [Member]
Disclosure of investment [line items]
Available-for-sale investments	2,575	1,437	2,878
Level 3 [Member]
Disclosure of investment [line items]
Available-for-sale investments	14	16	15
Sterling [Member]
Disclosure of investment [line items]
Investments in term deposits denominated in currencies	416	35	10
Sterling [Member] | Level 2 [Member]
Disclosure of investment [line items]
Available-for-sale investments	2,180	900	2,430
USD [Member]
Disclosure of investment [line items]
Investments in term deposits denominated in currencies	27	30	30
Other Currencies [Member]
Disclosure of investment [line items]
Investments in term deposits denominated in currencies	4	18
Euros [Member] | Level 2 [Member]
Disclosure of investment [line items]
Available-for-sale investments	£ 395	£ 537	£ 448

XML

Investments - Fair Value Hierarchy of Investments (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Non-current and current investments
Available-for-sale investments	£ 2,621	£ 1,474	£ 2,917
Fair value through profit or loss	7	7	7
Total	2,628	1,481	2,924
Level 1 [Member]
Non-current and current investments
Available-for-sale investments	32	21	24
Fair value through profit or loss	7	7	7
Total	39	28	31
Level 2 [Member]
Non-current and current investments
Available-for-sale investments	2,575	1,437	2,878
Total	2,575	1,437	2,878
Level 3 [Member]
Non-current and current investments
Available-for-sale investments	14	16	15
Total	£ 14	£ 16	£ 15

XML

Cash and Cash Equivalents - Summary of Cash and Cash Equivalents (Detail) - GBP (£) £ in Millions		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2015
Disclosure of cash and cash equivalents [line items]
Cash at bank and in hand		£ 439	£ 467	£ 893
Loans and receivables
Total cash equivalents		82	59	96
Total cash and cash equivalents		521	526	989
Bank overdrafts		(29)	(17)	(537)
Cash and cash equivalents per the cash flow statement	[1]	492	509	452	£ 402
US Deposits [Member]
Loans and receivables
Other deposits		26	32	44
UK Deposits [Member]
Loans and receivables
Other deposits		31	1	20
Other Deposits [Member]
Loans and receivables
Other deposits		£ 25	£ 26	£ 32

[1] Net of bank overdrafts of £29m (2016/17: £17m, 2015/16: £537m).

XML

Cash and Cash Equivalents - Additional Information (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Cash and Cash Equivalents [Line Items]
Restricted cash	£ 32	£ 43	£ 51
Held In Countries Prevent From Accessing Cash Balance [Member]
Cash and Cash Equivalents [Line Items]
Restricted cash	29	41	44
Held in Escrow Accounts or in Commercial Arrangements [Member]
Cash and Cash Equivalents [Line Items]
Restricted cash	£ 3	£ 2	£ 7

XML

Loans and Other Borrowings - Summary of Key Components of External Gross Debt (Detail) £ in Millions	12 Months Ended
	Mar. 31, 2018 GBP (£)
Disclosure Of Detailed Information About Borrowings [Line Items]
At 1 April 2017 £m	£ 10,980
Issuance/ (maturities) £m	2,175
Foreign exchange £m	10
Accrued interest movements £m	10
At 31 March 2018 £m	13,175
2018 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
At 1 April 2017 £m	2,632
Issuance/ (maturities) £m	(1,401)
Fair value movements £m	(18)
Foreign exchange £m	(95)
Transfer to within one year £m	1,163
At 31 March 2018 £m	2,281
Over 12 Months [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
At 1 April 2017 £m	10,081
Issuance/ (maturities) £m	3,760
Fair value movements £m	(60)
Foreign exchange £m	(440)
Transfer to within one year £m	(1,347)
At 31 March 2018 £m	11,994
Cash Flows From Derivatives Related to Net Debt [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Issuance/ (maturities) £m	(188)
Transfer to within one year £m	188
Overdrafts [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Issuance/ (maturities) £m	4
Transfer to within one year £m	(4)
Impact of Cross-currency Swaps [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
At 1 April 2017 £m	(1,419)
Foreign exchange £m	545
At 31 March 2018 £m	(874)
Removal of the Accrued Interest and Fair Value [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
At 1 April 2017 £m	(314)
Fair value movements £m	78
Accrued interest movements £m	10
At 31 March 2018 £m	£ (226)

XML

Loans and Other Borrowings - Summary of Reconciliation From Most Directly Comparable IFRS Measure to Net Debt (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	£ 13,491	£ 11,405	£ 12,457
Finance leases	223	229	233
Acquisition facility			181
Other loans	532	710	561
Bank overdrafts (note 22)	29	17	537
Amounts due to ultimate company	1,061	1,183	1,024
Total other loans and borrowings	1,622	2,262	3,095
Total loans and borrowings	15,336	13,896	15,785
1.625% Bond Due June 2016 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds			419
8.50% Bond Due December 2016 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds			696
3.5% Bond Due February 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds			398
1.25% Bond Due February 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds			348
6.625% Bond Due June 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds		526	525
5.95% Bond Due January 2018 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds		891	775
3.25% Bond Due August 2018 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	541	539	510
2.35% Bond Due February 2019 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	572	642	558
4.38% Bond Due March 2019 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	455	460	464
1.125% Bond Due June 2019 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	883	863	800
8.625% Bond Due March 2020 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	300	300	300
0.625% Bond Due March 2021 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	1,309	1,282	1,190
0.5% Bond Due June 2022 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	502
1.125% Bond Due March 2023 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	961	942	873
1% Bond Due June 2024 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	506
1% Bond Due November 2024 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	959
3.50% Index Linked Bond Due April 2025 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	419	403	396
1.75% Bond Due March 2026 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	1,137	1,113	1,032
1.5% Bond Due June 2027 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	1,009
5.75% Bond Due December 2028 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	721	731	741
9.125% Bond Due December 2030 (Minimum 8.625%) [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	1,943	2,191	1,910
3.125% Bond Due November 2031 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	502
6.375% Bond Due June 2037 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	522	522	522
3.625% bond due November 2047 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total listed bonds	£ 250
LIBOR Plus 0.95% Syndicated Loan Facilities Due April 2016 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loan due			438
2.21% Bank Loan Due December 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loan due		£ 352	£ 354

XML

Loans and Other Borrowings - Summary of Reconciliation From Most Directly Comparable IFRS Measure to Net Debt (Parenthetical) (Detail) € in Millions, £ in Millions, $ in Millions	12 Months Ended
	Mar. 31, 2018 GBP (£)	Mar. 31, 2017 GBP (£)	Mar. 31, 2016 GBP (£)	Mar. 31, 2018 USD ($)	Mar. 31, 2018 EUR (€)	Mar. 31, 2017 USD ($)	Mar. 31, 2017 EUR (€)	Mar. 31, 2016 USD ($)	Mar. 31, 2016 EUR (€)
Disclosure Of Detailed Information About Borrowings [Line Items]
Upgrade rating percentage	0.25%
Downgrade rating percentage	0.25%
1.625% Bond Due June 2016 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | $								$ 600
Loans and borrowings, interest rate			1.625%					1.625%	1.625%
Loans and borrowings, original currency			USD
Loans and borrowings, maturity			June 2016
8.50% Bond Due December 2016 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount			£ 678
Loans and borrowings, interest rate			8.50%					8.50%	8.50%
Loans and borrowings, original currency			GBP
Loans and borrowings, maturity			December 2016
8.50% Bond Due December 2016 [Member] | Bottom of Range [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, interest rate			7.50%					7.50%	7.50%
3.5% Bond Due February 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €									€ 500
Loans and borrowings, interest rate			3.50%					3.50%	3.50%
Loans and borrowings, original currency			EUR
Loans and borrowings, maturity			February 2017
1.25% Bond Due February 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | $								$ 500
Loans and borrowings, interest rate			1.25%					1.25%	1.25%
Loans and borrowings, original currency			USD
Loans and borrowings, maturity			February 2017
6.625% Bond Due June 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount		£ 500	£ 500
Loans and borrowings, interest rate		6.625%	6.625%			6.625%	6.625%	6.625%	6.625%
Loans and borrowings, original currency		GBP	GBP
Loans and borrowings, maturity		June 2017	June 2017
5.95% Bond Due January 2018 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | $						$ 1,100		$ 1,100
Loans and borrowings, interest rate		5.95%	5.95%			5.95%	5.95%	5.95%	5.95%
Loans and borrowings, original currency		USD	USD
Loans and borrowings, maturity		January 2018	January 2018
3.25% Bond Due August 2018 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 600		€ 600		€ 600
Loans and borrowings, interest rate	3.25%	3.25%	3.25%	3.25%	3.25%	3.25%	3.25%	3.25%	3.25%
Loans and borrowings, original currency	EUR	EUR	EUR
Loans and borrowings, maturity	August 2018	August 2018	August 2018
2.35% Bond Due February 2019 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | $				$ 800		$ 800		$ 800
Loans and borrowings, interest rate	2.35%	2.35%	2.35%	2.35%	2.35%	2.35%	2.35%	2.35%	2.35%
Loans and borrowings, original currency	USD	USD	USD
Loans and borrowings, maturity	February 2019	February 2019	February 2019
4.38% Bond Due March 2019 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 450	£ 450	£ 450
Loans and borrowings, interest rate	4.38%	4.38%	4.38%	4.38%	4.38%	4.38%	4.38%	4.38%	4.38%
Loans and borrowings, original currency	GBP	GBP	GBP
Loans and borrowings, maturity	March 2019	March 2019	March 2019
1.125% Bond Due June 2019 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 1,000		€ 1,000		€ 1,000
Loans and borrowings, interest rate	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%
Loans and borrowings, original currency	EUR	EUR	EUR
Loans and borrowings, maturity	June 2019	June 2019	June 2019
8.625% Bond Due March 2020 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 300	£ 300	£ 300
Loans and borrowings, interest rate	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%
Loans and borrowings, original currency	GBP	GBP	GBP
Loans and borrowings, maturity	March 2020	March 2020	March 2020
0.625% Bond Due March 2021 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 1,500		€ 1,500		€ 1,500
Loans and borrowings, interest rate	0.625%	0.625%	0.625%	0.625%	0.625%	0.625%	0.625%	0.625%	0.625%
Loans and borrowings, original currency	EUR	EUR	EUR
Loans and borrowings, maturity	March 2021	March 2021	March 2021
0.5% Bond Due June 2022 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 575
Loans and borrowings, interest rate	0.50%			0.50%	0.50%
Loans and borrowings, original currency	EUR
Loans and borrowings, maturity	June 2022
1.125% Bond Due March 2023 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 1,100		€ 1,100		€ 1,100
Loans and borrowings, interest rate	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%	1.125%
Loans and borrowings, original currency	EUR	EUR	EUR
Loans and borrowings, maturity	March 2023	March 2023	March 2023
1% Bond Due June 2024 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 575
Loans and borrowings, interest rate	1.00%			1.00%	1.00%
Loans and borrowings, original currency	EUR
Loans and borrowings, maturity	June 2024
1% Bond Due November 2024 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 1,100
Loans and borrowings, interest rate	1.00%			1.00%	1.00%
Loans and borrowings, original currency	EUR
Loans and borrowings, maturity	November 2024
3.50% Index Linked Bond Due April 2025 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 250	£ 250	£ 250
Loans and borrowings, interest rate	3.50%	3.50%	3.50%	3.50%	3.50%	3.50%	3.50%	3.50%	3.50%
Loans and borrowings, original currency	GBP	GBP	GBP
Loans and borrowings, maturity	April 2025	April 2025	April 2025
1.75% Bond Due March 2026 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 1,300		€ 1,300		€ 1,300
Loans and borrowings, interest rate	1.75%	1.75%	1.75%	1.75%	1.75%	1.75%	1.75%	1.75%	1.75%
Loans and borrowings, original currency	EUR	EUR	EUR
Loans and borrowings, maturity	March 2026	March 2026	March 2026
1.5% Bond Due June 2027 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | €					€ 1,150
Loans and borrowings, interest rate	1.50%			1.50%	1.50%
Loans and borrowings, original currency	EUR
Loans and borrowings, maturity	June 2027
5.75% Bond Due December 2028 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 600	£ 600	£ 600
Loans and borrowings, interest rate	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%	5.75%
Loans and borrowings, original currency	GBP	GBP	GBP
Loans and borrowings, maturity	December 2028	December 2028	December 2028
9.125% Bond Due December 2030 (Minimum 8.625%) [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount | $				$ 2,670		$ 2,670		$ 2,670
Loans and borrowings, interest rate	9.125%	9.125%	9.125%	9.125%	9.125%	9.125%	9.125%	9.125%	9.125%
Loans and borrowings, original currency	USD	USD	USD
Loans and borrowings, maturity	December 2030	December 2030	December 2030
9.125% Bond Due December 2030 (Minimum 8.625%) [Member] | Bottom of Range [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, interest rate	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%	8.625%
3.125% Bond Due November 2031 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 500	£ 500	£ 500
Loans and borrowings, interest rate	3.125%	3.125%	3.125%	3.125%	3.125%	3.125%	3.125%	3.125%	3.125%
Loans and borrowings, original currency	GBP	GBP	GBP
Loans and borrowings, maturity	November 2031	November 2031	November 2031
6.375% Bond Due June 2037 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 500	£ 500	£ 500
Loans and borrowings, interest rate	6.375%	6.375%	6.375%	6.375%	6.375%	6.375%	6.375%	6.375%	6.375%
Loans and borrowings, original currency	GBP	GBP	GBP
Loans and borrowings, maturity	June 2037	June 2037	June 2037
3.625% bond due November 2047 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount	£ 250
Loans and borrowings, interest rate	3.625%			3.625%	3.625%
Loans and borrowings, original currency	GBP
Loans and borrowings, maturity	November 2047
LIBOR Plus 0.95% Syndicated Loan Facilities Due April 2016 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount			£ 438
Loans and borrowings, maturity			April 2016
Loans and borrowings, LIBOR interest rate			0.95%					0.95%	0.95%
2.21% Bank Loan Due December 2017 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Loans and borrowings, face amount		£ 350	£ 350
Loans and borrowings, interest rate		2.21%	2.21%			2.21%	2.21%	2.21%	2.21%
Loans and borrowings, maturity		December 2017	December 2017

XML

Loans and Other Borrowings - Additional Information (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Detailed Information About Borrowings [Line Items]
Fair value of listed bonds and other long-term borrowings	£ 15,336	£ 13,896	£ 15,785
Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Principal repayments of loans and borrowings at hedged rate	14,219	12,138	14,756
At Fair Value [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Fair value of listed bonds and other long-term borrowings	14,878	13,496	14,500
Fair value of finance leases	£ 253	£ 273	£ 284

XML

Loans and Other Borrowings - Summary Of Loans and Other Borrowings (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Current liabilities
Listed bonds	£ 1,702	£ 1,539	£ 2,013
Finance leases	18	15	8
Bank loans		352
Syndicated loan facilities			619
Other loans and bank overdrafts	561	726	1,096
Amounts due to ultimate parent company	17	159	20
Total current liabilities	2,298	2,791	3,756
Non-current liabilities
Listed bonds	11,789	9,866	10,444
Finance leases	205	214	225
Bank loans			354
Other loans		1	2
Amounts due to ultimate parent company	1,044	1,024	1,004
Total non-current liabilities	13,038	11,105	12,029
Total	£ 15,336	£ 13,896	£ 15,785

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Loans and Other Borrowings - Summary Of Loans and Other Borrowings (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Detailed Information About Borrowings [Abstract]
Collateral received on swaps	£ 525	£ 702	£ 553

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Loans and Other Borrowings - Summary of Principal Repayments of Loans and Other Borrowings (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	£ 13,038	£ 11,105	£ 12,029
Total	15,336	13,896	15,785
Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Within one year, or on demand	2,289	2,791	3,756
Total	15,263	13,746	15,606
Fair value adjustments	73	150	179
Total loans and other borrowings	15,336	13,896	15,785
Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Within one year, or on demand	(308)	(523)	(252)
Total	(1,044)	(1,608)	(850)
Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Within one year, or on demand	1,981	2,268	3,504
Total	14,219	12,138	14,756
2018 [Member] | Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	1,192	1,614	1,632
2018 [Member] | Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	(66)	(197)	(216)
2018 [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	1,126	1,417	1,416
2019 [Member] | Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	1,332	1,166	1,488
2019 [Member] | Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	(154)	(43)	(72)
2019 [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	1,178	1,123	1,416
2020 [Member] | Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	18	1,295	1,103
2020 [Member] | Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year		(121)	18
2020 [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	18	1,174	1,121
2021 [Member] | Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	1,489	12	1,199
2021 [Member] | Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	(111)		(26)
2021 [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	1,378	12	1,173
2023 [Member] | Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	8,943	6,868	6,428
2023 [Member] | Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	(405)	(724)	(302)
2023 [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	8,538	6,144	6,126
Over 12 Months [Member] | Carrying Amount [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	12,974	10,955	11,850
Over 12 Months [Member] | Effect Of Hedging And Interest
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	(736)	(1,085)	(598)
Over 12 Months [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Total due for repayment after more than one year	£ 12,238	£ 9,870	£ 11,252

XML

Loans and Other Borrowings - Summary of Obligations Under Finance Leases (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Detailed Information About Borrowings [Line Items]
Amounts payable under finance leases	£ 348	£ 368	£ 383
Less: future finance charges	(129)	(139)	(150)
Fair value adjustments for purchase price adjustment	4
Total finance lease obligations	223	229	233
Repayment of outstanding lease obligations	219	229	233
Fair value adjustments for purchase price adjustment	4
Total finance lease obligations	223	229	233
2018 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Amounts payable under finance leases	33	29	13
Repayment of outstanding lease obligations	18	14	8
Between Two and Five Years [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Amounts payable under finance leases	122	102	105
Repayment of outstanding lease obligations	71	50	51
2023 [Member]
Disclosure Of Detailed Information About Borrowings [Line Items]
Amounts payable under finance leases	193	237	265
Repayment of outstanding lease obligations	£ 130	£ 165	£ 174

XML

Finance Expense - Summary of Finance Expense and Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Interest on:
Financial liabilities at amortised cost and associated derivatives	£ 478	£ 567	£ 489
Finance leases	16	15	14
Derivatives	14	12	11
Fair value movements on derivatives not in a designated hedge relationship	1	(2)	(5)
Reclassification of cash flow hedge from other comprehensive income	34	(1)	3
Unwinding of discount on provisions	15	16	8
Interest payable on ultimate parent company borrowings	18	25	20
Total finance expense	794	842	769
Specific items	218	210	229
Interest on available-for-sale investments	5	6	8
Interest on loans and receivables	7	7	6
Other interest and similar income			23
Interest income on loans to immediate and ultimate parent company	203	219	352
Total finance income	215	232	389
Net finance expense	579	610	380
Before Specific Items [Member]
Interest on:
Total finance expense	576	632	540
Total finance income	215	232	389
Net finance expense	£ 361	£ 400	£ 151

XML

Financial Instruments and Risk Management - Additional Information (Detail) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Minimum percentage of fixed rate debt on total debt	70.00%
Description of reasonable benchmarks for performing sensitivity analysis	For interest, a 1% increase in interest rates and parallel shift in yield curves across Sterling, US Dollar and Euro currencies. – For foreign exchange, a 10% strengthening/weakening in Sterling against other currencies.
Percentage of reasonably possible increase in interest rate assumption	1.00%
Percentage of reasonably possible increase decrease in Sterling against other currencies	10.00%
Impact on net annual finance expense due to a 1% change in interest rate	£ 143,000,000	£ 108,000,000	£ 123,000,000
Percentage of interest accrued	0.25%
Notional value of debt outstanding	£ 1,900,000,000
Expected change in financial expenses	10,000,000
Term debt	2,298,000,000	2,791,000,000	3,756,000,000
Energy Derivative Contract [Member] | Designated in a Cash Flow Hedge [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Loss on energy contract deferred	8,000,000
Fair value of the energy derivative	1,000,000	8,000,000	0
Currency Swap Contract and Interest Rate Swap [Member] | Credit Support Agreements [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Fair value notional amount	3,162,000,000
Net cash inflow from netting and credit support agreements	220,000,000	100,000,000	79,000,000
Individually Insignificant Counterparties [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Cash collateral held	492,000,000	702,000,000	553,000,000
Non-Financial Assets [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Non-current trade and other receivables	317,000,000	360,000,000	218,000,000
Prepayments and Other Receivables [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Non-current trade and other receivables	1,496,000,000	1,106,000,000	1,103,000,000
Debt Maturing in September 2021 [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Undrawn committed borrowing facilities	£ 2,100,000,000	£ 2,100,000,000	£ 1,500,000,000
Debt maturity	September 2021
2018 [Member]
Disclosure of Nature and Extent of Risks Arising From Financial Instruments [Line Items]
Term debt	£ 1,600,000,000

XML

Financial Instruments and Risk Management - Summary of Currency and Interest Rate Profile of Loans and Borrowings (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of credit risk exposure [Line Items]
Ratio of fixed to floating	100.00%	100.00%	100.00%
Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	£ 14,219	£ 12,138	£ 14,756
Sterling [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	13,710	11,497	14,169
Euros [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	£ 509	£ 641	£ 587
Fixed Interest Rate [Member]
Disclosure of credit risk exposure [Line Items]
Ratio of fixed to floating	84.00%	79.00%	77.00%
fixed interest rate – Sterling	4.40%	4.90%	6.00%
Fixed Interest Rate [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	£ 11,990	£ 9,633	£ 11,417
Fixed Interest Rate [Member] | Sterling [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	£ 11,990	£ 9,633	£ 11,417
Floating Interest Rate [Member]
Disclosure of credit risk exposure [Line Items]
Ratio of fixed to floating	16.00%	21.00%	23.00%
Floating Interest Rate [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	£ 2,229	£ 2,505	£ 3,339
Floating Interest Rate [Member] | Sterling [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	1,720	1,864	2,752
Floating Interest Rate [Member] | Euros [Member] | Principal Repayment at Hedged Rates [Member]
Disclosure of credit risk exposure [Line Items]
Principal repayments of loans and borrowings at hedged rate	£ 509	£ 641	£ 587

XML

Financial Instruments and Risk Management - Summary of Impact on Equity, Before Tax, of a 1% Increase in Interest (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Sterling Interest Rates [Member]
Disclosure Of Foreign Currency Exchange Exposure [Line Items]
Interest rate increase (reduce)	£ 628	£ 554	£ 626
US Dollar Interest Rates [Member]
Disclosure Of Foreign Currency Exchange Exposure [Line Items]
Interest rate increase (reduce)	(267)	(348)	(374)
Euro Interest Rates [Member]
Disclosure Of Foreign Currency Exchange Exposure [Line Items]
Interest rate increase (reduce)	(401)	(229)	(263)
Sterling Strengthening [Member]
Disclosure Of Foreign Currency Exchange Exposure [Line Items]
Interest rate increase (reduce)	£ (236)	£ (269)	£ (98)

XML

Financial Instruments and Risk Management - Summary of Credit Ratings (Detail)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Moodys [Member]
Disclosure of external credit grades [Line Items]
Rating	Baa2	Baa1	Baa2
Outlook	Stable	Negative	Positive
Standard And Poor's [Member]
Disclosure of external credit grades [Line Items]
Rating	BBB+	BBB+	BBB
Outlook	Negative	Negative	Positive

XML

Financial Instruments and Risk Management - Summary of Remaining Contractually-Agreed Cash Flows Including Interest Payable for Non-Derivative Financial Liabilities on Undiscounted Basis (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	£ 15,167	£ 13,707	£ 15,587
Interest on loans and other borrowings	169	189	198
Trade and other payables	4,961	5,298	5,346
Provisions	300	292	296
Total	20,597	19,486	21,427
Gross Carrying Amount [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	15,094	13,557	15,408
Interest on loans and other borrowings	5,316	4,683	4,841
Trade and other payables	4,961	5,298	5,346
Provisions	372	469	462
Total	25,743	24,007	26,057
Gross Carrying Amount [Member] | 2018 [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	2,120	2,602	3,558
Interest on loans and other borrowings	468	532	513
Trade and other payables	4,961	5,298	5,346
Provisions	54	62	50
Total	7,603	8,494	9,467
Gross Carrying Amount [Member] | 2018 [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	1,192	1,614	1,632
Interest on loans and other borrowings	421	415	435
Provisions	34	41	30
Total	1,647	2,070	2,097
Gross Carrying Amount [Member] | 2019 [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	1,332	1,166	1,488
Interest on loans and other borrowings	381	364	357
Provisions	25	21	25
Total	1,738	1,551	1,870
Gross Carrying Amount [Member] | 2020 [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	18	1,295	1,103
Interest on loans and other borrowings	374	327	343
Provisions	43	18	15
Total	435	1,640	1,461
Gross Carrying Amount [Member] | 2021 [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	1,489	12	1,199
Interest on loans and other borrowings	372	319	308
Provisions	19	17	16
Total	1,880	348	1,523
Gross Carrying Amount [Member] | 2023 [Member]
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	8,943	6,868	6,428
Interest on loans and other borrowings	3,300	2,726	2,885
Provisions	197	310	326
Total	12,440	9,904	9,639
Interest Payments Not Yet Accrued
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Interest on loans and other borrowings	(5,147)	(4,494)	(4,643)
Total	(5,147)	(4,494)	(4,643)
Fair Value Adjustments
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Loans and other borrowings	73	150	179
Total	73	150	179
Impact Of Discounting
Disclosure of maturity analysis for non-derivative financial liabilities [Line Items]
Provisions	(72)	(177)	(166)
Total	£ (72)	£ (177)	£ (166)

XML

Financial Instruments and Risk Management - Summary of Contractually Agreed Cash Flows in Respect of Derivative Financial Instruments (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Derivatives-Analysed by Earliest Payment Date [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	£ 1,210	£ 1,174	£ 1,187
Derivatives-Analysed by Earliest Payment Date [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	1,026	1,126	1,166
Derivatives-Analysed by Earliest Payment Date [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(3,366)	(1,673)	(1,338)
Derivatives-Analysed by Earliest Payment Date [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	3,550	1,721	1,359
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	180	297	281
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	140	291	268
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(547)	(576)	(250)
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	587	582	263
Derivatives-Analysed by Earliest Payment Date [Member] | 2019 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	152	198	382
Derivatives-Analysed by Earliest Payment Date [Member] | 2019 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	156	198	371
Derivatives-Analysed by Earliest Payment Date [Member] | 2019 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(446)		(27)
Derivatives-Analysed by Earliest Payment Date [Member] | 2019 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	442		38
Derivatives-Analysed by Earliest Payment Date [Member] | 2020 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	166	114	62
Derivatives-Analysed by Earliest Payment Date [Member] | 2020 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	143	114	60
Derivatives-Analysed by Earliest Payment Date [Member] | 2020 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(29)		(836)
Derivatives-Analysed by Earliest Payment Date [Member] | 2020 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	52		838
Derivatives-Analysed by Earliest Payment Date [Member] | 2021 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	184	104	80
Derivatives-Analysed by Earliest Payment Date [Member] | 2021 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	161	104	81
Derivatives-Analysed by Earliest Payment Date [Member] | 2021 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(29)		(18)
Derivatives-Analysed by Earliest Payment Date [Member] | 2021 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	52		17
Derivatives-Analysed by Earliest Payment Date [Member] | 2023 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	376	123	(15)
Derivatives-Analysed by Earliest Payment Date [Member] | 2023 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	291	123
Derivatives-Analysed by Earliest Payment Date [Member] | 2023 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(2,149)		(180)
Derivatives-Analysed by Earliest Payment Date [Member] | 2023 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	2,234		165
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	152	338	397
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	135	296	386
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(166)	(1,097)	(27)
Derivatives-Analysed by Earliest Payment Date [Member] | 2018 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	183	1,139	38
Derivatives-Analysed Based on Holding Instrument to Maturity [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	1,210	1,174	1,187
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	1,026	1,126	1,166
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(3,366)	(1,673)	(1,338)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	3,550	1,721	1,359
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	131	98	104
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	91	92	91
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(547)	(576)	(250)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	587	582	263
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2019 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	107	92	99
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2019 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	85	92	88
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2019 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(47)		(27)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2019 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	69		38
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2020 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	101	88	92
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2020 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	80	88	90
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2020 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(47)		(836)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2020 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	68		838
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2021 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	101	83	83
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2021 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	80	83	84
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2021 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(47)		(18)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2021 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	68		17
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2023 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	662	679	710
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2023 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	599	679	725
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2023 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(2,512)		(180)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2023 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	2,575		165
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	108	134	99
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member] | Net Settled [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	91	92	88
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member] | Gross Settled Inflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	(166)	(1,097)	(27)
Derivatives-Analysed Based on Holding Instrument to Maturity [Member] | 2018 [Member] | Gross Settled Outflows [Member]
Disclosure of maturity analysis for derivative financial liabilities [Line Items]
Derivative financial liabilities net settled	£ 183	£ 1,139	£ 38

XML

Financial Instruments and Risk Management - Summary of Maximum Credit Risk Exposure of Financial Assets (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of credit risk exposure [Line Items]
Maximum credit risk exposure	£ 21,141	£ 18,872	£ 20,748
Derivative Financial Assets [Member]
Disclosure of credit risk exposure [Line Items]
Maximum credit risk exposure	1,509	2,246	1,639
Investments [Member]
Disclosure of credit risk exposure [Line Items]
Maximum credit risk exposure	16,578	13,346	15,236
Trade and Other Receivables [Member]
Disclosure of credit risk exposure [Line Items]
Maximum credit risk exposure	2,533	2,754	2,884
Cash and Cash Equivalent [Member]
Disclosure of credit risk exposure [Line Items]
Maximum credit risk exposure	£ 521	£ 526	£ 989

XML

Financial Instruments and Risk Management - Summary of Credit Quality and Credit Concentration of Cash Equivalents, Current Asset Investments and Derivative Financial Assets (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure of external credit grades [Line Items]
Credit exposure	£ 4,613	£ 3,825	£ 4,653
Aa2/AA and Above [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	2,575	1,444	2,878
Aa3/AA- [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	313	208	120
A1/A+ [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	651	952	64
A2/A [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	628	370	939
A3/A [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	180	204	160
Baa1/BBB+ [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	59	561	£ 492
Baa2/BBB and Below [Member]
Disclosure of external credit grades [Line Items]
Credit exposure	£ 207	£ 86

XML

Financial Instruments and Risk Management - Summary of Offsetting of Financial Assets and Liabilities (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Offsetting Of Financial Assets Liabilities [Abstract]
Amounts presented in the balance sheet, derivative financial liabilities	£ (837)	£ (903)	£ (911)
Rights of set off with derivative counterparties, derivative financial liabilities	754	693	456
Cash collateral, derivative financial liabilities	60	64	40
Net amount, derivative financial liabilities	(23)	(146)	(415)
Amounts presented in the balance sheet	672	1,343	728
Right of set off with derivative counterparties	0	0	0
Cash collateral	(432)	(638)	(513)
Net amount	240	705	215
Amounts presented in the balance sheet, derivative financial assets	1,509	2,246	1,639
Right of set off with derivative counterparties,derivative financial assets	(754)	(693)	(456)
Cash collateral, derivative financial assets	(492)	(702)	(553)
Net amount, derivative financial assets	£ 263	£ 851	£ 630

XML

Financial Instruments and Risk Management - Summary of Derivative Financial Instruments are Held at Fair Value on Balance Sheet (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Derivative Financial Instruments [Line Items]
Current asset	£ 197	£ 428	£ 177
Non-current asset	1,312	1,818	1,462
Current liability	50	34	48
Non-current liability	787	869	863
Designated in a Cash Flow Hedge [Member]
Disclosure Of Derivative Financial Instruments [Line Items]
Current asset	187	417	166
Non-current asset	1,061	1,508	1,158
Current liability	41	25	40
Non-current liability	587	616	618
Other [Member]
Disclosure Of Derivative Financial Instruments [Line Items]
Current asset	10	11	11
Non-current asset	251	310	304
Current liability	9	9	8
Non-current liability	£ 200	£ 253	£ 245

XML

Other Reserves - Summary of Other Reserves (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Reserves Within Equity [Line Items]
Beginning balance	£ 18,926	£ 21,325	£ 19,277
Recognised in income and expense	(34)	1	(3)
Tax recognised in other comprehensive income	345	(445)	235
Ending balance	22,740	18,926	21,325
Other Reserves [Member]
Disclosure Of Reserves Within Equity [Line Items]
Beginning balance	1,591	1,392	1,209
Exchange differences	(188)	227	29
Net fair value gain on cash flow hedges	(368)	884	381
Recognised in income and expense	277	(938)	(230)
Fair value movement on available-for-sale assets	11	(3)	(2)
Tax recognised in other comprehensive income	1	29	5
Transfer to realised profit	(83)
Ending balance	1,241	1,591	1,392
Other Reserves [Member] | Cash Flow Reserve [Member]
Disclosure Of Reserves Within Equity [Line Items]
Beginning balance	127	173	55
Net fair value gain on cash flow hedges	(368)	884	381
Recognised in income and expense	277	(938)	(230)
Tax recognised in other comprehensive income	10	8	(33)
Transfer to realised profit	(83)
Ending balance	(37)	127	173
Other Reserves [Member] | Available-for-Sale Reserve [Member]
Disclosure Of Reserves Within Equity [Line Items]
Beginning balance	13	16	18
Fair value movement on available-for-sale assets	11	(3)	(2)
Ending balance	24	13	16
Other Reserves [Member] | Translation Reserve [Member]
Disclosure Of Reserves Within Equity [Line Items]
Beginning balance	593	345	278
Exchange differences	(188)	227	29
Tax recognised in other comprehensive income	(9)	21	38
Ending balance	396	593	345
Other Reserves [Member] | Merger and Other Reserves [Member]
Disclosure Of Reserves Within Equity [Line Items]
Beginning balance	858	858	858
Ending balance	£ 858	£ 858	£ 858

XML

Other Reserves - Summary of Other Reserves (Parenthetical) (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Other Reserves [Member] | Cash Flow Reserve [Member]
Disclosure Of Reserves Within Equity [Line Items]
Net charge to cash flow reserve relating to fair value movements on derivatives	£ 295	£ (941)	£ (255)
Non-controlling interests [member]
Disclosure Of Reserves Within Equity [Line Items]
Exchange differences in relation to retained earnings attributed to non-controlling interests	£ 1	£ 10	£ 0

XML

Directors' Emoluments and Pensions - Additional Information (Detail)	12 Months Ended
	Mar. 31, 2018 GBP (£) £ / shares shares	Mar. 31, 2017 GBP (£)
Disclosure Of Defined Benefit Plans [Line Items]
Deferred bonuses payable to directors	£ 319,000	£ 88,000
Aggregate emoluments excluding deferred bonus	£ 2,525,000	£ 1,149,000
Number of directors with accrued retirement benefits under a money purchase scheme	0	1
Top of Range [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Deferred bonuses payable to directors	£ 302,400	£ 36,000
Aggregate emoluments excluding deferred bonus	£ 1,538,000	£ 492,000
BT Group Share Options Plan [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of director exercise options	0	0
Nuber of options vested	£ 179,000	£ 2,646,000
BT Long Term Incentive Plans [Member]
Disclosure Of Defined Benefit Plans [Line Items]
Number of director exercise options	6	3
Number of shares entitled to receive highest paid director | shares	1,612,997
Ordinary shares nominal value | £ / shares	£ 0.05

XML

Related Party Transactions - Additional Information (Detail) - GBP (£)	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016	Apr. 01, 2018	Mar. 31, 2002
Disclosure Of Transactions Between Related Parties [Line Items]
Dividends paid		£ 2,350,000,000	£ 1,450,000,000
Loan facility [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Applicable margin to LIBOR	1.025%
Loan facility [Member] | Top of Range [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Interest receivable on loan facilities	£ 25,000,000,000
Loan facility [Member] | Bottom of Range [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Interest receivable on loan facilities	10,000,000,000
British Telecommunications plc [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Investment in the company					£ 18,500,000,000
Dividends paid	£ 0	2,350,000,000	1,450,000,000
Final dividend declared		£ 0	2,350,000,000
British Telecommunications plc [Member] | Events After Reporting Period [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Final dividend declared				£ 2,500,000,000
Ultimate Parent Company [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Equity placing			£ 1,000,000,000

XML

Related Party Transactions - Balances with Parent and Ultimate Parent Companies and Finance Income or Expense (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Transactions Between Related Parties [Line Items]
Non-current assets investments	£ 13,354	£ 11,606	£ 11,965
Non-current liabilities loans	(13,038)	(11,105)	(12,029)
Trade and other receivables	15	25	9
Current asset investments	3,224	1,740	3,271
Current liabilities loans	(2,298)	(2,791)	(3,756)
Finance income	215	232	389
Finance (expense)	(794)	(842)	(769)
British Telecommunications plc [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Non-current assets investments	10,318	10,191	10,510
Non-current liabilities loans	(14,916)	(16,874)
Current asset investments	168	192	327
Trade and other payables	(50)	(63)	(70)
Current liabilities loans	(18,494)	(19,999)
Finance income	169	191	326
Ultimate Parent Company [Member]
Disclosure Of Transactions Between Related Parties [Line Items]
Non-current assets investments	2,983	1,371	1,409
Non-current liabilities loans	(1,044)	(1,024)	(1,004)
Trade and other receivables	15	25	9
Current asset investments	34	28	26
Current liabilities loans	(18)	(159)	(20)
Finance income	34	28	26
Finance (expense)	£ (18)	£ (25)	£ (20)

XML

Related Party Transactions - Balances with Parent and Ultimate Parent Companies and Finance Income or Expense (Parenthetical) (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Transactions Between Related Parties [Abstract]
Net cash outflow on non-current amounts owed by ultimate parent company		£ 1,722
Cash inflow on non-current amounts owed from ultimate parent company		45
Cash outflow on non-current amounts owed by ultimate parent company	[1]	1,677	£ 1,571	£ 4,767
Non cash movements on non current asset investments		£ 63

[1] Refer to note 28 for further information.

XML

Financial Commitments and Contingent Liabilities - Disclosure of Financial Commitments (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017
Financial Commitments [Abstract]
Capital commitments	£ 993	£ 889
Other commitments	362	367
Device purchase commitments	262	423
TV programme rights commitments	2,823	2,644
Total	£ 4,440	£ 4,323

XML

Financial Commitments and Contingent Liabilities - Disclosure of Future Minimum Operating Lease Payments (Detail) - GBP (£) £ in Millions	Mar. 31, 2018	Mar. 31, 2017
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	£ 6,597	£ 7,160
2018 [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments		650
2019 [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	600	610
2020 [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	550	558
2021 [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	513	532
2022 [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	486	505
2023 [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	463	475
Thereafter [Member]
Disclosure Of Operating Leases Future Minimum Payments [Line Items]
Future minimum operating lease payments	£ 3,985	£ 3,830

XML

Financial Commitments and Contingent Liabilities - Additional Information (Detail) - GBP (£) £ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2016	May 31, 2016	Mar. 31, 2018	Mar. 31, 2017
Disclosure of Financial Commitments [Line Items]
Average lease term			14 years	15 years
Average fixed rental term			14 years	15 years
Deemed consent charge, net			£ 300.0
Brazilian Tax Authority [Member]
Disclosure of Financial Commitments [Line Items]
value of claim			219.0
Brazilian Tax Authority [Member] | One case that covers the period 2013 to 2016 [Member]
Disclosure of Financial Commitments [Line Items]
value of claim			1.2
Brazilian Tax Authority [Member] | Eight cases took place on 21 February 2018 [Member]
Disclosure of Financial Commitments [Line Items]
value of claim			£ 43.0
Phones 4U Limited [Member]
Disclosure of Financial Commitments [Line Items]
Sharing of revenue under retail trading agreement due date	2019-09
Sharing of related payment under retail trading agreement due date	2021-04
Hutchinson 3G Limited [Member]
Disclosure of Financial Commitments [Line Items]
Claimed damages relating to loss of business		£ 167.0

XML

Post Balance Sheet Events - Additional Information (Detail)		1 Months Ended	12 Months Ended
	Apr. 01, 2018 GBP (£)	May 31, 2018 GBP (£) Role	Mar. 31, 2018 GBP (£) Employee	Mar. 31, 2017 GBP (£) Employee	Mar. 31, 2016 GBP (£) Employee	Apr. 30, 2018 MHz GHz
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue			£ 23,723,000,000	£ 24,062,000,000	£ 19,012,000,000
Internal cost			£ 20,339,000,000	£ 20,892,000,000	£ 15,397,000,000
Year end | Employee			105,800	106,400	102,500
Average | Employee			106,200	105,000	91,000
Accrued income			£ 777,000,000	£ 955,000,000	£ 1,072,000,000
Cash in excess of deposits			21,000,000
Ofcom [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Deposit with Ofcom			325,000,000
Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			£ 1,251,000,000	£ 1,184,000,000	£ 1,152,000,000
Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Year end | Employee			18,200	17,900	15,700
Average | Employee			18,000	16,800	7,600
Accrued income			£ 208,000,000	£ 260,000,000	£ 395,000,000
Consumer [Member] | Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			£ 363,000,000	£ 463,000,000	£ 405,000,000
Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Year end | Employee			13,900	14,100	14,000
Average | Employee			14,200	13,900	13,100
Accrued income			£ 279,000,000	£ 318,000,000	£ 245,000,000
Enterprise [Member] | Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			£ 345,000,000	£ 275,000,000	£ 191,000,000
Events After Reporting Period [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Frequency of spectrum secured | MHz						40
Total frequeny of spectrum | GHz						3.4
Spectrum acquisition cost	£ 304,000,000
Announcing Or Commencing Implementation of Major Restructuring [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Reduction in back office and middle management roles related to restructuring programme		£ 800,000,000
Reduction payback period		2 years
Expected cash cost reduction related to restructuring programme		£ 1,500,000,000
Cost of balances of restructuring programme		£ 60,000,000
Number of removal of full time equivalent roles | Role		1,200
Further run rate synergies related to ee integration programme		£ 110,000,000
BT Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Year end | Employee			8,800	8,700	6,700
Average | Employee			8,800	7,700	6,300
Accrued income			£ 86,000,000	£ 90,000,000	£ 83,000,000
BT Consumer [Member] | Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			£ 157,000,000	£ 128,000,000	£ 138,000,000
EE [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Year end | Employee			9,400	9,200	9,000
Average | Employee			9,200	9,100	1,300
Accrued income			£ 122,000,000	£ 170,000,000	£ 312,000,000
EE [Member] | Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			206,000,000	335,000,000	267,000,000
Business and Public Sector [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Accrued income			134,000,000	151,000,000	146,000,000
Business and Public Sector [Member] | Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			253,000,000	200,000,000	115,000,000
Wholesale and Ventures [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Accrued income			145,000,000	167,000,000	99,000,000
Wholesale and Ventures [Member] | Current [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Trade receivables not past due			92,000,000	75,000,000	76,000,000
Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue			3,330,000,000	3,396,000,000	3,323,000,000
Elimination of Intersegment Amounts [Member] | Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue			(103,000,000)	(100,000,000)	(72,000,000)
Internal cost			963,000,000	973,000,000	978,000,000
Elimination of Intersegment Amounts [Member] | BT Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost			959,000,000	970,000,000	965,000,000
Elimination of Intersegment Amounts [Member] | BT Consumer [Member] | Events After Reporting Period [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	0
Internal cost	0
Elimination of Intersegment Amounts [Member] | EE [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue			37,000,000	37,000,000	7,000,000
Elimination of Intersegment Amounts [Member] | EE [Member] | Events After Reporting Period [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	0
Internal cost	£ 0
Elimination of Intersegment Amounts [Member] | Business and Public Sector [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue			32,000,000	22,000,000	24,000,000
Internal cost			32,000,000	22,000,000	24,000,000
Elimination of Intersegment Amounts [Member] | Wholesale and Ventures [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue			32,000,000	22,000,000	24,000,000
Internal cost			£ 32,000,000	£ 22,000,000	£ 24,000,000

XML

Post Balance Sheet Events - Summary of Segment Analysis Outlining Impacts which Change in Segment Revenue and Profit (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		£ 23,723	£ 24,062	£ 19,012
Depreciation and amortisation		(3,514)	(3,510)	(2,631)
Operating profit (loss)		3,384	3,170	3,615
Net finance expense	[1]	(579)	(610)	(380)
Share of post tax loss of associates and joint ventures		(1)	(9)	6
Profit (loss) before taxation		2,804	2,551	3,241
Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[2]	23,746	24,082	18,879
EBITDA	[3]	7,508	7,648	6,458
Depreciation and amortisation		(3,514)	(3,510)	(2,631)
Operating profit (loss)	[2]	3,994	4,138	3,827
Net finance expense		(361)	(400)	(151)
Profit (loss) before taxation		3,632	3,729	3,682
Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[4]	(23)	(20)	133
Operating profit (loss)	[4]	(610)	(968)	(212)
Net finance expense	[4]	(218)	(210)	(229)
Profit (loss) before taxation	[4]	(828)	(1,178)	(441)
Segment Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		27,044	27,456	22,178
Segment Revenue [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		27,076	27,478	22,202
Internal Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		(3,298)	(3,374)	(3,299)
Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Depreciation and amortisation		(992)	(989)	(353)
Consumer [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[2]	10,257	9,924	5,377
EBITDA	[3]	2,376	2,168	1,228
Operating profit (loss)	[2]	1,384	1,179	875
Consumer [Member] | Segment Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		10,360	10,024	5,449
Consumer [Member] | Internal Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		(103)	(100)	(72)
Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Depreciation and amortisation		(676)	(658)	(537)
Enterprise [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[2]	6,323	6,607	6,375
EBITDA	[3]	2,172	2,362	2,169
Operating profit (loss)	[2]	1,496	1,704	1,632
Enterprise [Member] | Segment Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		6,540	6,845	6,544
Enterprise [Member] | Internal Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		(217)	(238)	(169)
Global Services [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Depreciation and amortisation		(424)	(439)	(422)
Global Services [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[2]	5,013	5,479	5,074
EBITDA	[3]	434	495	479
Depreciation and amortisation		(424)	(439)	(422)
Operating profit (loss)	[2]	10	56	57
Global Services [Member] | Segment Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		5,013	5,479	5,074
Global Services [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		5,013	5,479	5,074
Openreach [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Depreciation and amortisation		(1,360)	(1,369)	(1,301)
Openreach [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[2]	2,145	2,062	2,042
EBITDA	[3]	2,520	2,633	2,659
Depreciation and amortisation		(1,360)	(1,369)	(1,301)
Operating profit (loss)	[2]	1,160	1,264	1,358
Openreach [Member] | Segment Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		5,123	5,098	5,100
Openreach [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		5,123	5,098	5,100
Openreach [Member] | Internal Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		(2,978)	(3,036)	(3,058)
Other [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Depreciation and amortisation		(62)	(55)	(18)
Other [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue	[2]	8	10	11
EBITDA	[3]	6	(10)	(77)
Depreciation and amortisation		(62)	(55)	(18)
Operating profit (loss)	[2]	(56)	(65)	(95)
Other [Member] | Segment Revenue [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		8	10	11
Other [Member] | Segment Revenue [Member] | Before Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Revenue		£ 8	£ 10	£ 11

[1] Net finance expense includes specific item expense of £218m (2016/17: £210m, 2015/16: £229m).

[2] Before specific items.

[3] EBITDA is stated before specific items and is the group’s profitability measure for segments.

[4] a For a definition of specific items, see page 209. An analysis of specific items is provided in note 8.

XML

Post Balance Sheet Events - Summary of Segment Analysis Outlining Impacts which Change in Segment Revenue and Profit (Parenthetical) (Detail) - GBP (£) £ in Millions		12 Months Ended
		Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Specific item expense		£ 794	£ 842	£ 769
Specific Items [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Specific item expense	[1]	£ 218	£ 210	£ 229

[1] a For a definition of specific items, see page 209. An analysis of specific items is provided in note 8.

XML

Post Balance Sheet events - Summary of Segment Analysis Outlining Impacts which Change in Internal Revenue and Costs (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	£ 20,339	£ 20,892	£ 15,397
Internal revenue	(23,723)	(24,062)	(19,012)
Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	(3,330)	(3,396)	(3,323)
Elimination of Intersegment Amounts [Member] | Global Services [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	187	240	236
Elimination of Intersegment Amounts [Member] | Other [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	1,599	1,564	1,472
Consumer [Member] | Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	963	973	978
Internal revenue	103	100	72
Consumer [Member] | Elimination of Intersegment Amounts [Member] | Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	67	63	73
Internal revenue	65	62	31
Consumer [Member] | Elimination of Intersegment Amounts [Member] | Global Services [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	20	20	23
Consumer [Member] | Elimination of Intersegment Amounts [Member] | Openreach [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	896	910	905
Consumer [Member] | Elimination of Intersegment Amounts [Member] | Other [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	18	18	18
Enterprise [Member] | Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	507	558	557
Internal revenue	217	238	169
Enterprise [Member] | Elimination of Intersegment Amounts [Member] | Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	65	62	31
Internal revenue	67	63	73
Enterprise [Member] | Elimination of Intersegment Amounts [Member] | Global Services [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	42	62	40
Enterprise [Member] | Elimination of Intersegment Amounts [Member] | Openreach [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	442	496	526
Internal revenue	42	39	56
Enterprise [Member] | Elimination of Intersegment Amounts [Member] | Other [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	66	74
Global Services [Member] | Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	187	240	236
Global Services [Member] | Elimination of Intersegment Amounts [Member] | Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	20	20	23
Global Services [Member] | Elimination of Intersegment Amounts [Member] | Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	42	62	40
Global Services [Member] | Elimination of Intersegment Amounts [Member] | Openreach [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	125	158	173
Openreach [Member] | Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	42	39	56
Internal revenue	2,978	3,036	3,058
Openreach [Member] | Elimination of Intersegment Amounts [Member] | Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	896	910	905
Openreach [Member] | Elimination of Intersegment Amounts [Member] | Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	42	39	56
Internal revenue	442	496	526
Openreach [Member] | Elimination of Intersegment Amounts [Member] | Global Services [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	125	158	173
Openreach [Member] | Elimination of Intersegment Amounts [Member] | Other [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	1,515	1,472	1,454
Other [Member] | Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	1,599	1,564	1,472
Other [Member] | Elimination of Intersegment Amounts [Member] | Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	18	18	18
Other [Member] | Elimination of Intersegment Amounts [Member] | Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	66	74
Other [Member] | Elimination of Intersegment Amounts [Member] | Openreach [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal cost	1,515	1,472	1,454
Internal Revenue [Member] | Elimination of Intersegment Amounts [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Internal revenue	£ 3,298	£ 3,374	£ 3,299

XML

Post Balance Sheet events - Summary of Segment Analysis Outlining Impacts which Change in Capital Expenditure (Detail) - GBP (£) £ in Millions	12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2016
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	£ 3,522	£ 3,454	£ 2,622
Property, Plant and Equipment [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	2,880	2,833	2,210
Intangible Assets [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	642	621	412
Consumer [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	919	853	303
Consumer [Member] | Property, Plant and Equipment [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	683	628	186
Consumer [Member] | Intangible Assets [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	236	225	117
Enterprise [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	533	501	362
Enterprise [Member] | Property, Plant and Equipment [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	353	360	256
Enterprise [Member] | Intangible Assets [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	180	141	106
Global Services [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	278	361	355
Global Services [Member] | Property, Plant and Equipment [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	186	235	293
Global Services [Member] | Intangible Assets [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	92	126	62
Openreach [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	1,658	1,573	1,447
Openreach [Member] | Property, Plant and Equipment [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	1,588	1,499	1,385
Openreach [Member] | Intangible Assets [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	70	74	62
Other [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	134	166	155
Other [Member] | Property, Plant and Equipment [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	70	111	90
Other [Member] | Intangible Assets [Member]
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]
Capital expenditure	£ 64	£ 55	£ 65