UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                   FORM 6-K

                        REPORT OF FOREIGN PRIVATE ISSUER
                       PURSUANT TO RULE 13a-16 OR 15d-16
                     UNDER THE SECURITIES EXCHANGE ACT OF 1934


                          For the month of April, 2007

                           SPIRENT COMMUNICATIONS plc
     _____________________________________________________________________
                (Translation of registrant's name into English)

  Spirent House, Crawley Business Quarter, Fleming Way, Crawley, West Sussex
                                RH10 9QL, UK.
     _____________________________________________________________________
                    (Address of principal executive offices)


Indicate by check mark whether the registrant files or will file annual reports
under cover Form 20-F or Form 40-F.

                         Form 20-F    X         Form 40-F.....

Indicate by check mark whether the registrant by furnishing the information
contained in this Form is also thereby furnishing the information to the
Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

                               Yes .....        No     X

If "Yes" is marked, indicate below the file number assigned to the registrant
in connection with Rule 12g3-2(b): 82- ________












                                                                                         

TR-1(i):               Notification of major interests in shares

1. Identity of the issuer or the underlying issuer of existing   Spirent Communications plc
shares to which voting rights are attached(ii):

2. Reason for the notification     (please tick the appropriate box or boxes)

An acquisition or disposal of voting rights                                                       x
An acquisition or disposal of financial instruments which may result in the acquisition of
shares already issued to which voting rights are attached
An event changing the breakdown of voting rights
Other (please specify):___________________________________________

3. Full name of person(s) subject to the notification obligation  Lehman Brothers International (Europe)
(iii):

4. Full name of shareholder(s) (if different from 3.)(iv):                          N/A

5. Date of the transaction (and date on which the threshold is                 20 April 2007
crossed or reached if different)(v):

6. Date on which issuer notified:                                              25 April 2007

7. Threshold(s) that is/are crossed or reached:                                     3%

8. Notified details:                                                             N/A






A: Voting rights attached to shares
Class/type of     Situation previous to the Resulting situation after the triggering transaction(vii)
shares            Triggering transaction
                  (vi)
if possible using Number of     Number of   Number of    Number of voting rights  % of voting rights
the ISIN CODE     Shares        Voting      shares       ix
                                Rights viii Direct       Direct  x    Indirect xi Direct      Indirect


 Ordinary Shares   24,437,613   24,437,613   34,174,456   34,174,456      N/A        3.88%        N/A

  GB0004726096


B: Financial Instruments
Resulting situation after the triggering transaction xii
Type of financial    Expiration date Exercise/ Conversion      Number of voting rights    % of voting
instrument           xiii            Period/ Date xiv          that may be acquired if    rights
                                                               the instrument is
                                                               exercised/ converted.


                                                   N/A


Total (A+B)
Number of voting rights                            % of voting rights


34,174,456                                         3.88%






9. Chain of controlled undertakings through which the voting rights and/or the financial instruments are effectively
held, if applicable xv:
                                                          N/A



Proxy Voting:
10. Name of the proxy holder:                                  N/A
11. Number of voting rights proxy holder will cease to hold:   N/A
12. Date on which proxy holder will cease to hold voting       N/A
rights:
13. Additional information:                 N/A
14. Contact name:                           Tara O'Hagan
15. Contact telephone number:               +44 (0) 20 7102 1832


C:        Additional information


Contact at Issuer: Michael Anscombe, Deputy Company Secretary,
Spirent Communications plc

Telephone: 01293 767676






- --------------------------


NOTES:



(i)           This form is to be sent to the issuer or underlying issuer and to
be filed with the competent authority.


(ii)           Either the full name of the legal entity or another method for
identifying the issuer or underlying issuer, provided it is reliable and
accurate.


(iii)          This should be the full name of (a) the shareholder; (b) the
person acquiring, disposing of or exercising voting rights in the cases provided
for in DTR5.2.1 (b) to (h);  (c) all the parties to the agreement referred to in
DTR5.2.1 (a), or (d) the direct or indirect holder of financial instruments
entitled to acquire shares already issued to which voting rights are attached,
as appropriate.

In relation to the transactions referred to in points DTR5.2.1 (b) to (h), the
following list is provided as indication of the persons who should be mentioned:

- -           in the circumstances foreseen in  DTR5.2.1 (b), the person that
acquires the voting rights and is entitled to exercise them under the agreement
and the natural person or legal entity who is transferring temporarily for
consideration the voting rights;

- -           in the circumstances foreseen in DTR 5.2.1 (c), the person holding
the collateral, provided the person or entity controls the voting rights and
declares its intention of exercising them, and person lodging the collateral
under these conditions;

- -           in the circumstances foreseen in DTR5.2.1(d), the person who has a
life interest in shares if that person is entitled to exercise the voting rights
attached to the shares and the person who is disposing of the voting rights when
the life interest is created;

- -           in the circumstances foreseen in DTR5.2.1 (e), the parent
undertaking and, provided it has a notification duty at an individual level
under DTR 5.1, under DTR5.2.1 (a) to (d) or under a combination of any of those
situations, the controlled undertaking;

- -           in the circumstances foreseen in DTR5.2.1 (f), the deposit taker of
the shares, if he can exercise the voting rights attached to the shares
deposited with him at his discretion, and the depositor of the shares allowing
the deposit taker to exercise the voting rights at his discretion;

- -           in the circumstances foreseen in DTR5.2.1 (g), the person  that
controls the voting rights;

- -           in the circumstances foreseen in DTR5.2.1 (h), the proxy holder, if
he can exercise the voting rights at his discretion, and the shareholder who has
given his proxy to the proxy holder allowing the latter to exercise the voting
rights at his discretion.


(iv)          Applicable in the cases provided for in DTR 5.2.1 (b) to (h). This
should be the full name of the shareholder or holder of financial instruments
who is the counterparty to the natural person or legal entity referred to in
DTR5.2.


(v)           The date of the transaction should normally be, in the case of an
on exchange transaction, the date on which the matching of orders occurs; in the
case of an off exchange transaction, date of the entering into an agreement.

The date on which threshold is crossed should normally be the date on which the
acquisition, disposal or possibility to exercise voting rights takes effect (see
DTR 5.1.1R (3)). For passive crossings, the date when the corporate event took
effect.

These dates will usually be the same unless the transaction is subject to a
condition beyond the control of the parties.


(vi)          Please refer to the situation disclosed in the previous
notification, In case the situation previous to the triggering transaction was
below 3%, please state 'below 3%'.

vii         If the holding has fallen below the minimum threshold , the
notifying party should not be obliged to disclose the extent of the holding,
only that the new holding is less than 3%.


For the case provided for in DTR5.2.1(a), there should be no disclosure of
individual holdings per party to the agreement unless a party individually
crosses or reaches an Article 9 threshold. This applies upon entering into,
introducing changes to or terminating an agreement.

viii           Direct and indirect

ix          In case of combined holdings of shares with voting rights attached '
direct holding' and voting rights 'indirect holdings', please split the voting
rights number and percentage into the direct and indirect columns-if there is no
combined holdings, please leave the relevant box blank.

X          Voting rights attached to shares in respect of which the notifying
party is a direct shareholder  (DTR 5.1)

xi             Voting rights held by the notifying party as an indirect
shareholder (DTR 5.2.1)

xii         If the holding has fallen below the minimum threshold, the notifying
party should not be obliged to disclose the extent of the holding, only that the
new holding is below 3%.

xiii         date of maturity / expiration of the finical instrument i.e. the
date when the right to acquire shares ends.

xiv            If the financial instrument has such a period-please specify the
period- for example once every three months starting from the (date)

xv          The notification should include the name(s) of the controlled
undertakings through which the voting rights are held. The notification should
also include the amount of voting rights and the percentage held by each
controlled undertaking, insofar as individually the controlled undertaking holds
3% or more, and insofar as the notification by the parent undertaking is
intended to cover the notification obligations of the controlled undertaking.

xvi         This annex is only to be filed with the competent authority.

xvii        Whenever another person makes the notification on behalf of the
shareholder or the natural person/legal entity  referred to in DTR5.2 and
DTR5.3.

                                   Signatures

Pursuant to the requirements of the Securities Exchange Act of 1934, the
registrant has duly caused this report to be signed on its behalf by the
undersigned, thereunto duly authorized.

                                               ______MICHAEL ANSCOMBE______

                                                     (Registrant)

Date: 25 April, 2007                      By   ____/s/ Michael Anscombe____

                                                    (Signature)*