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 October, 2004

                                 SPIRENT 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- ________ 





                                  




                                SCHEDULE 10

                   NOTIFICATION OF MAJOR INTERESTS IN SHARES


1. Name of company

SPIRENT PLC


2. Name of shareholder having a major interest

FIDELITY INTERNATIONAL LIMITED


3. Please state whether notification indicates that it is in respect of holding
of the shareholder named in 2 above or 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

COMPANY NAMED IN BOX 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

CHASE MANHATTAN BANK LONDON TOTAL (FIL)                          579,749
DEUTSCHE BANK TOTAL (FIL)                                     48,076,139
NORTHERN TRUST TOTAL (FIL)                                       192,674
JP MORGAN TOTAL (FISL)                                           196,866

TOTAL                                                         49,045,428

FISL = Fidelity Investment Services Limited
FIL = Fidelity International Limited


5. Number of shares / amount of stock acquired

NOT KNOWN


6. Percentage of issued class

NOT KNOWN


7. Number of shares / amount of stock disposed

-


8. Percentage of issued class

-


9. Class of security

ORDINARY SHARES OF 3.3333 PENCE EACH


10. Date of transaction

NOT NOTIFIED


11. Date company informed

15 OCTOBER 2004


12. Total holding following this notification

49,045,428


13. Total percentage holding of issued class following this notification

5.14%


14. Any additional information

SHAREHOLDER NAMED IN BOX 2 ABOVE PREVIOUSLY REPORTED A NOTIFIABLE INTEREST OF
4.01% IN THE ISSUED SHARE CAPITAL OF THE COMPANY ON 29 SEPTEMBER 2004


15. Name of contact and telephone number for queries

LUKE THOMAS - 01293 767658


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

LUKE THOMAS - DEPUTY COMPANY SECRETARY


Date of notification

15 OCTOBER 2004


The FSA does not give any express or implied warranty as to the accuracy of this
document or material and does not accept any liability for error or omission.
The FSA is not liable for any damages (including, without limitation, damages
for loss of business or loss of profits) arising in contract, tort or otherwise
from the use of or inability to use this document, or any material contained in
it, or from any action or decision taken as a result of using this document or
any such material.


 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 15 October, 2004                       By   ____/s/ Luke Thomas____

                                                    (Signature)*