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)*