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, 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- ________ BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: SPIRENT EXECUTIVE SHARE OPTION SCHEME Period of return: From: 1 JANUARY 2005 : 30 JUNE 2005 Balance under scheme from previous 4,521,734 ORDINARY SHARES OF return: 3 1/3p EACH The amount by which the block scheme NIL has been increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted 1,720,460 ORDINARY SHARES OF under scheme during period: 3 1/3p EACH Balance under scheme not yet 2,801,274 ORDINARY SHARES OF issued/allotted at end of period: 3 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: U.S EMPLOYEE STOCK PURCHASE PLAN Period of return: From: 1 JANUARY 2005 TO: 30 JUNE 2005 Balance under scheme from previous 3,701,676 ORDINARY SHARES OF return: 3 1/3p EACH The amount by which the block scheme NIL has been increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted 2,464,312 ORDINARY SHARES OF under scheme during period: 3 1/3p EACH Balance under scheme not yet 1,237,364 ORDINARY SHARES OF issued/allotted at end of period: 3 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: SPIRENT GLOBAL ALL EMPLOYEE SHARE PURCHASE PLAN Period of return: From: 1 JANUARY 2005 To: 30 JUNE 2005 Balance under scheme from previous 1,032,044 ORDINARY SHARES OF return: 3 1/3p EACH The amount by which the block scheme NIL has been increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted 217,600 ORDINARY SHARES OF 3 under scheme during period: 1/3p EACH Balance under scheme not yet 814,444 ORDINARY SHARES OF 3 issued/allotted at end of period: 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: NETCOM AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JANUARY 2005 TO: 30 JUNE 2005 Balance under scheme from previous 4,779,180 ORDINARY SHARES OF return: 3 1/3p EACH The amount by which the block scheme NIL has been increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted 399,516 ORDINARY SHARES OF 3 under scheme during period: 1/3p EACH Balance under scheme not yet 4,379,664 ORDINARY SHARES OF issued/allotted at end of period: 3 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: ZARAK AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JANUARY 2005 To: 30 JUNE 2005 Balance under scheme from previous 2,690,996 ORDINARY SHARES OF return: 3 1/3p EACH The amount by which the block scheme NIL has been increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted NIL under scheme during period: Balance under scheme not yet 2,690,996 ORDINARY SHARES OF issued/allotted at end of period: 3 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: SPIRENT SAVINGS RELATED SHARE OPTION SCHEME Period of return: From: 1 JANUARY 2005 To: 30 JUNE 2005 Balance under scheme from previous 180,812 ORDINARY SHARES OF 3 return: 1/3p EACH The amount by which the block NIL scheme has been increased, if the scheme has been increased since the date of the last return: Number of securities 66,424 ORDINARY SHARES OF 3 issued/allotted under scheme during 1/3p EACH period: Balance under scheme not yet 114,388 ORDINARY SHARES OF 3 issued/allotted at end of period: 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: SPIRENT STOCK INCENTIVE PLAN Period of return: From: 1 JANUARY 2005 To: 30 JUNE 2005 Balance under scheme from previous 4,461,376 ORDINARY SHARES OF return: 3 1/3p EACH The amount by which the block scheme 4,000,000 ORDINARY SHARES OF has been increased, if the scheme 3 1/3 p EACH has been increased since the date of the last return: Number of securities issued/allotted 2,951,731 ORDINARY SHARES OF under scheme during period: 3 1/3p EACH Balance under scheme not yet 5,509,645 ORDINARY SHARES OF issued/allotted at end of period: 3 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 8 July 2005 Name of applicant: SPIRENT PLC Name of scheme: CAW AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JANUARY 2005 To: 30 JUNE 2005 Balance under scheme from previous 878,101 ORDINARY SHARES OF 3 return: 1/3p EACH The amount by which the block scheme NIL has been increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted 22,551 ORDINARY SHARES OF 3 under scheme during period: 1/3p EACH Balance under scheme not yet 855,550 ORDINARY SHARES OF 3 issued/allotted at end of period: 1/3p EACH Number and class of securities 3,000,000 ORDINARY SHARES OF originally listed and the date of 3 1/3p EACH DATED 29 admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Total number of securities in issue 964,084,259 at the end of the period : Name of contact: Michael Anscombe Address of contact: Spirent plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY M Anscombe, Assistant Company Secretary_____________________________ Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent plc_______________________________________________ Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. END 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 08 July 2005 By ____/s/ Luke Thomas____ (Signature)*