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 July, 2006

                           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- ________



                   NOTIFICATION OF MAJOR INTERESTS IN SHARES


1. Name of listed company

SPIRENT COMMUNICATIONS PLC


2. Name of shareholder with a major interest

FIDELITY INTERNATIONAL LIMITED


3. Please state whether notification indicates that regarding the holding of the
shareholder named in 2 above; in respect of a non-beneficial interest; or in the
case of an individual holder if it is a holding of that person's spouse or
children under the age of 18

SHAREHOLDER IN 2 ABOVE AND ITS DIRECT AND INDIRECT SUBSIDIARIES, BEING
NON-BENEFICIAL HOLDERS


4. Name of the registered holder(s) and, if more than one holder, the number of
shares held by each of them


                                                                
JP MORGAN BOURNEMOUTH (FISL)                                       29,925,465
BROWN BROS HARRIMN LTD LUX (FIL)                                   11,517,334
JP MORGAN, BOURNEMOUTH (FII)                                        1,863,020
BNP PARIBAS, PARIS (FIGEST)                                         2,401,300
TOTAL                                                              45,707,119


FISL = Fidelity Investment Services Limited
FIL = Fidelity International Limited
FII = Fidelity Investments International
FIGEST = Fidelity Gestion


5. Number of shares / amount of stock acquired

-


6. Percentage of issued class (any treasury shares held by the listed company
should not be taken into account when calculating percentage)

-


7. Number of shares / amount of stock disposed

NOT KNOWN


8. Percentage of issued class (any treasury shares held by the listed company
should not be taken into account when calculating percentage)

NOT KNOWN


9. Class of security

ORDINARY SHARES OF 3.3333 PENCE EACH


10. Date of transaction

NOT KNOWN


11. Date company informed

11 JULY 2006


12. Total holding following this notification

45,707,119


13. Total percentage holding of issued class following this notification (any
treasury shares held by the listed company should not be taken into account when
calculating percentage)

4.84%


14. Any additional information

ON 04 JULY 2006 THE SHAREHOLDER REPORTED TO THE COMPANY THAT IT HAD REDUCED ITS
HOLDING IN THE COMPANY TO 56,076,114 SHARES (5.90%).


15. Name of contact and telephone number for queries

MICHAEL ANSCOMBE - 01293 767672


16. Name and signature of duly authorised company official of the listed company
responsible for making this notification

MICHAEL ANSCOMBE - DEPUTY COMPANY SECRETARY


Date of notification

12 JULY 2006





                                   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.

                                               ______LUKE THOMAS______

                                                     (Registrant)

Date __12 July 2006                             By   ____/s/ Luke Thomas____

                                                    (Signature)*