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 January, 2005

                                   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

BARCLAYS PLC


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

SHAREHOLDER NAMED IN 2 ABOVE


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



      Registered Holder           Account designation       Holding 
                                                                 
      BANK OF IRELAND                  4239730              289,266     
      BANK OF IRELAND                  4239749              645,114     
      BANK OF NEW YORK                 214075             5,207,031   
      BANK OF NEW YORK                 221428               742,541     
      BANK OF NEW YORK                 367748             2,653,825   
      BANK OF NEW YORK                 392067             3,094,403   
      BANK OF NEW YORK                 392177               405,953     
      BANK OF NEW YORK                 768198               216,933     
      BARCLAYS CAPITAL NOMINEES LIMI                        986,870     
      BNP PARIBAS                                            57,625      
      BNY (OCS) NOMINEES LTD           221476               205,774     
      BNY (OCS) NOMINEES LTD           387173                71,285      
      BOISS NOMINEES LTD               4224361              398,025     
      CHASE NOMINEES LTD               16376                527,631     
      CHASE NOMINEES LTD               16669                134,728     
      CHASE NOMINEES LTD               18243                123,823     
      CHASE NOMINEES LTD               19518                306,837     
      CHASE NOMINEES LTD               19519              2,287,823   
      CHASE NOMINEES LTD               20947             37,657,633  
      CHASE NOMINEES LTD               21359              1,483,196   
      CHASE NOMINEES LTD               25772                740,598     
      CHASE NOMINEES LTD               27793                 82,603      
      CHASE NOMINEES LTD               27795                102,621     
      CHASE NOMINEES LTD               27797                138,568     
      CHASE NOMINEES LTD               27799                299,495     
      CHASE NOMINEES LTD               27800              1,037,801   
      CHASE NOMINEES LTD               27802                 26,754      
      CHASE NOMINEES LTD               27804                 26,545      
      CHASE NOMINEES LTD               28270                365,798     
      CHASE NOMINEES LTD               28270              1,054,929   
      CHASE NOMINEES LTD               31961              2,125,084   
      CIBC MELLON GLOBAL SECURITIES                          47,233      
      CITIBANK                         6010613363            86,613      
      CITIBANK                         6010640794           253,843     
      CITIBANK                         6010782807           433,211     
      DEUTSCHE BANK LONDON             8003168               30,331      
      HSBC                             813168               796,049     
      HSBC                             814537                80,198      
      HSBC                             845315                23,453      
      INVESTORS BANK AND TRUST CO                           915,354     
      INVESTORS BANK AND TRUST CO                           619,882     
      INVESTORS BANK AND TRUST CO                            14,730      
      INVESTORS BANK AND TRUST CO                            47,333      
      INVESTORS BANK AND TRUST CO                         4,894,733   
      INVESTORS BANK AND TRUST CO                         1,620,581   
      INVESTORS BANK AND TRUST CO                           126,144     
      JP MORGAN (BGI CUSTODY)          16331                351,468     
      JP MORGAN (BGI CUSTODY)          16341                593,372     
      JP MORGAN (BGI CUSTODY)          16341              1,841,753   
      JP MORGAN (BGI CUSTODY)          16344                605,254     
      JP MORGAN (BGI CUSTODY)          16345              1,032,894   
      JP MORGAN (BGI CUSTODY)          16400             10,298,369  
      JP MORGAN (BGI CUSTODY)          16612                289,986     
      JP MORGAN (BGI CUSTODY)          16621                241,168     
      JP MORGAN (BGI CUSTODY)          16644                297,267     
      JP MORGAN (BGI CUSTODY)          16901                149,752     
      JP MORGAN (BGI CUSTODY)          18409                484,895     
      JP MORGAN (BGI CUSTODY)          19514                 82,721      
      JP MORGAN (BGI CUSTODY)          20946                 35,336      
      JP MORGAN (BGI CUSTODY)          27795                228,835     
      JP MORGAN (BGI CUSTODY)          27799              1,124,484   
      JP MORGAN (BGI CUSTODY)          28166              3,027,976   
      JP MORGAN CHASE BANK                                  340,332     
      JP MORGAN CHASE BANK                                  190,590     
      JP MORGAN CHASE BANK                                  409,555     
      JP MORGAN CHASE BANK                                  633,980     
      JP MORGAN CHASE BANK                                  347,670     
      MELLON BANK                      ABGFZ872482          827,679     
      MELLON BANK                      TGGF0003002          101,154     
      MELLON TRUST - BOSTON & SF                            256,673     
      MELLON TRUST OF NEW ENGLAND                           320,175     
      MIDLAND BANK (HSBC BANK PLC)     772823             2,860,115   
      NORTHERN TRUST                   BCP04                 67,019      
      NORTHERN TRUST                   CVS21              1,120,589   
      NORTHERN TRUST                   SCO06                303,975     
      NORTHERN TRUST                   TNF01                481,183     
      NORTHERN TRUST                   USF06                193,023     
      NORTHERN TRUST                   USF12              1,509,895   
      NORTHERN TRUST BANK - BGI SEPA                        421,924     
      NORTHERN TRUST BANK - BGI SEPA                        300,968     
      NORTHERN TRUST BANK - BGI SEPA                         85,456      
      R C GREIG NOMINEES LIMITED A/C   BL1                  127,653     
      R C GREIG NOMINEES LIMITED A/C   CM1                   34,397      
      R C GREIG NOMINEES LIMITED GP1   GP1                   30,098      
      R C GREIG NOMINEES LIMITED SA1   SA1                   20,902      
      STATE STREET                     2RJ2                 127,458     
      STATE STREET                     JD12                 447,165     
      STATE STREET                     N3B6                  42,101      
      STATE STREET                     N3YZ                  10,972      
      ZEBAN NOMINEES LIMITED                                 21,700      
      ZEBAN NOMINEES LIMITED                                  1,000       
                                       TOTAL            105,807,731 



5. Number of shares / amount of stock acquired

NOT NOTIFIED


6. Percentage of issued class

NOT NOTIFIED


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

HOLDING AS AT 26 JANUARY 2005


11. Date company informed

27 JANUARY 2005


12. Total holding following this notification

105,807,731


13. Total percentage holding of issued class following this notification

11.03%


14. Any additional information

NOTIFICATION RECEIVED PURSUANT TO S198-202 COMPANIES ACT 1985 THAT THE 
SHAREHOLDER NAMED IN 2 ABOVE HAS INCREASED THEIR NOTIFIABLE SHAREHOLDING IN 
SPIRENT PLC TO 11.03%.  SHAREHOLDER PREVIOUSLY REPORTED A SHAREHOLDING OF 
97,113,892 SHARES (10.13%) ON 21 JANUARY 2005.


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

27 JANUARY 2005


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 __27 January 2005                    By   ____/s/ Luke Thomas____

                                                    (Signature)*