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- ________ BLOCKLISTING SIX MONTHLY RETURN To: The FSA Date: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: SPIRENT EXECUTIVE SHARE OPTION SCHEME, 1995 Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 2,386,034 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been 3,500,000 ORDINARY SHARES OF 3 1/3p EACH increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme 1,753,775 ORDINARY SHARES OF 3 1/3p EACH during period: Balance under scheme not yet issued/allotted at end 4,132,259 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 3,000,000 ORDINARY SHARES OF 3 1/3p EACH DATED 29 the date of admission: SEPTEMBER 2000 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 3,500,000 ORDINARY SHARES OF 3 1/3p EACH DATED 14 MARCH 2006 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: U.S EMPLOYEE STOCK PURCHASE PLAN Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 1,237,364 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme NIL during period: Balance under scheme not yet issued/allotted at end 1,237,364 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 435,000 ORDINARY SHARES OF 3 1/3p EACH DATED 5 JUNE the date of admission: 2001 3,500,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 1 NOVEMBER 2001 7,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 18 NOVEMBER 2002 1,800,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 6 DECEMBER 2004 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: SPIRENT GLOBAL ALL EMPLOYEE SHARE PURCHASE PLAN Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 814,444 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme NIL during period: Balance under scheme not yet issued/allotted at end 814,444 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 1,000,000 ORDINARY SHARES OF 3 1/3p EACH DATED 18 the date of admission: NOVEMBER 2002 700,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 6 DECEMBER 2004 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: NETCOM AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 4,200,894 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme 2,674,007 ORDINARY SHARES OF 3 1/3p EACH during period: Balance under scheme not yet issued/allotted at end 1,526,887 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 3,291,399 ORDINARY SHARES OF 3 1/3p EACH DATED 3 the date of admission: SEPTEMBER 1999 1,739,130 ORDINARY SHARES OF 3 1/3 p EACH DATED 8 JULY 2002 6,722,689 ORDINARY SHARES OF 3 1/3 p EACH DATED 8 OCTOBER 2002 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: ZARAK AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 2,690,996 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme NIL during period: Balance under scheme not yet issued/allotted at end 2,690,996 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 3,895,474 ORDINARY SHARES OF 3 1/3p EACH DATED 14 the date of admission: NOVEMBER 2000 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: SPIRENT SAVINGS RELATED SHARE OPTION SCHEME Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 68,185 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme NIL during period: Balance under scheme not yet issued/allotted at end 68,185 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 200,000 ORDINARY SHARES OF 3 1/3p EACH DATED 31 the date of admission: DECEMBER 2003 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: SPIRENT STOCK INCENTIVE PLAN Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 4,453,686 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme 589,855 ORDINARY SHARES OF 3 1/3p EACH during period: Balance under scheme not yet issued/allotted at end 3,863,831 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 3,720,930 ORDINARY SHARES OF 3 1/3p EACH DATED 1 the date of admission: OCTOBER 2003 3,703,703 ORDINARY SHARES OF 3 1/3 p EACH DATED 2 OCTOBER 2003 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications 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: 28 July 2006 Name of applicant: SPIRENT COMMUNICATIONS PLC Name of scheme: CAW AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JANUARY 2006 To: 30 JUNE 2006 Balance under scheme from previous return: 836,399 ORDINARY SHARES OF 3 1/3p EACH The amount by which the block scheme has been NIL increased, if the scheme has been increased since the date of the last return: Number of securities issued/allotted under scheme 2,914 ORDINARY SHARES OF 3 1/3p EACH during period: Balance under scheme not yet issued/allotted at end 833,485 ORDINARY SHARES OF 3 1/3p EACH of period: Number and class of securities originally listed and 1,300,000 ORDINARY SHARES OF 3 1/3p EACH DATED 15 the date of admission: AUGUST 2002 115,394 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 AUGUST 2002 Total number of securities in issue at the end of the 970,810,133 ORDINARY SHARES OF 3 1/3 p EACH period : Name of contact: Warren Nash Address of contact: Spirent Communications plc Spirent House Crawley Business Quarter Fleming Way Crawley, RH10 9QL Telephone number of contact: 01293 767676 SIGNED BY Warren Nash Director/company secretary/suitably experienced employee/duly authorised officer, for and on behalf of Spirent Communications plc Name of applicant If you knowingly or recklessly give false or misleading information you may be liable to prosecution. 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 28 July, 2006 By ____/s/ Luke Thomas____ (Signature)*