Cash flow statement - Narrative (Details) - GBP (£) £ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disclosure of cash flow statement [Abstract]
Cash and cash equivalents held by entity unavailable for use by group	£ 31	£ 37	£ 76

The amount of significant cash and cash equivalent balances held by the entity that are not available for use by the group. [Refer: Cash and cash equivalents]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 7
-IssueDate 2023-01-01
-Paragraph 48
-URI https://taxonomy.ifrs.org/xifrs-link?type=IAS&num=7&code=ifrs-tx-2023-en-r&anchor=para_48&doctype=Standard
-URIDate 2023-03-23

Name:	ifrs-full_CashAndCashEquivalentsHeldByEntityUnavailableForUseByGroup
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant