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 February, 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 4239749 1,084,302 BANK OF NEW YORK 214075 5,915,102 BANK OF NEW YORK 221428 866,143 BANK OF NEW YORK 367748 2,907,094 BANK OF NEW YORK 392067 3,326,323 BANK OF NEW YORK 392177 489,732 BANK OF NEW YORK 768198 216,933 BARCLAYS CAPITAL NOMINEES LIMI 565,420 BNP PARIBAS 219,175 BNY (OCS) NOMINEES LTD 221476 382,174 BNY (OCS) NOMINEES LTD 387173 71,285 BOISS NOMINEES LTD 4224361 406,490 CHASE NOMINEES LTD 16376 527,631 CHASE NOMINEES LTD 16669 134,728 CHASE NOMINEES LTD 18243 123,823 CHASE NOMINEES LTD 19518 379,214 CHASE NOMINEES LTD 19519 2,634,098 CHASE NOMINEES LTD 19520 213,550 CHASE NOMINEES LTD 20947 38,680,837 CHASE NOMINEES LTD 21359 1,483,196 CHASE NOMINEES LTD 25772 863,420 CHASE NOMINEES LTD 27793 66,723 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 28270 365,798 CHASE NOMINEES LTD 28270 1,172,155 CHASE NOMINEES LTD 31961 2,294,832 CIBC MELLON GLOBAL SECURITIES 132,574 CITIBANK 6010613363 86,613 CITIBANK 6010640794 253,843 CITIBANK 6010782807 462,289 DEUTSCHE BANK LONDON 8003168 30,331 HSBC 813168 869,384 HSBC 814537 80,198 HSBC 845315 23,453 INVESTORS BANK AND TRUST CO 67,293 INVESTORS BANK AND TRUST CO 1,095,438 INVESTORS BANK AND TRUST CO 2,358,360 INVESTORS BANK AND TRUST CO 6,980,817 INVESTORS BANK AND TRUST CO 708,218 INVESTORS BANK AND TRUST CO 14,730 INVESTORS BANK AND TRUST CO 128,304 JP MORGAN (BGI CUSTODY) 16331 351,468 JP MORGAN (BGI CUSTODY) 16341 2,025,059 JP MORGAN (BGI CUSTODY) 16341 593,372 JP MORGAN (BGI CUSTODY) 16344 705,203 JP MORGAN (BGI CUSTODY) 16345 1,191,612 JP MORGAN (BGI CUSTODY) 16400 10,298,369 JP MORGAN (BGI CUSTODY) 16612 415,341 JP MORGAN (BGI CUSTODY) 16621 277,635 JP MORGAN (BGI CUSTODY) 16644 636,237 JP MORGAN (BGI CUSTODY) 16901 181,820 JP MORGAN (BGI CUSTODY) 18409 469,969 JP MORGAN (BGI CUSTODY) 19514 175,421 JP MORGAN (BGI CUSTODY) 27795 445,925 JP MORGAN (BGI CUSTODY) 27799 1,267,446 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 550,285 MELLON BANK ABGFZ872482 827,679 MELLON BANK TGGF0003002 101,154 MELLON TRUST - BOSTON & SF 367,265 MELLON TRUST OF NEW ENGLAND 458,475 MIDLAND BANK (HSBC BANK PLC) 772823 3,318,353 NORTHERN TRUST BCP04 67,019 NORTHERN TRUST CVS21 1,242,437 NORTHERN TRUST SCO06 303,975 NORTHERN TRUST TNF01 532,061 NORTHERN TRUST USF06 193,023 NORTHERN TRUST USF12 1,681,150 NORTHERN TRUST BANK - BGI SEPA 510,728 NORTHERN TRUST BANK - BGI SEPA 586,640 NORTHERN TRUST BANK - BGI SEPA 116,798 R C GREIG NOMINEES LIMITED A/C BL1 119,587 R C GREIG NOMINEES LIMITED A/C CM1 33,409 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 200,097 STATE STREET N3YZ 27,706 ZEBAN NOMINEES LIMITED 21,700 ZEBAN NOMINEES LIMITED 1,000 TOTAL 115,783,982 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 16 FEBRUARY 2005 11. Date company informed 21 FEBRUARY 2005 12. Total holding following this notification 115,783,982 13. Total percentage holding of issued class following this notification 12.07% 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 12.07%. SHAREHOLDER PREVIOUSLY REPORTED A SHAREHOLDING OF 105,807,731 SHARES (11.03%) ON 27 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 21 FEBRUARY 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 21 February, 2005 By ____/s/ Luke Thomas____ (Signature)*