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 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: SPIRENT EXECUTIVE SHARE OPTION SCHEME Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 4,562,114 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme during 40,380 ORDINARY SHARES period: Balance under scheme not yet issued/allotted at end 4,521,734 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 3,000,000 ORDINARY SHARES OF 3 1/3p EACH DATED 29 securities) originally listed and the date of SEPTEMBER 2000 admission: 3,000,000 ORDINARY SHARES OF 3 1/3 p EACH DATED 28 MAY 2004 Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter Fleming Way Crawley, RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: U.S. EMPLOYEE STOCK PURCHASE PLAN Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 1,985,764 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme 84,088 ORDINARY SHARES during period: Balance under scheme not yet issued/allotted at end 3,701,676 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 435,000 ORDINARY SHARES OF 3 1/3p EACH securities) originally listed and the date of ADMITTED 5 JUNE 2001 admission: 3,500,000 ORDINARY SHARES OF 3 1/3p EACH ADMITTED 1 NOVEMBER 2001 7,000,000 ORDINARY SHARES OF 3 1/3p EACH ADMITTED 18 NOVEMBER 2002 1,800,000 ORDINARY SHARES OF 3 1/3 p EACH ADMITTED 6 DECEMBER 2004 Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: GLOBAL ALL EMPLOYEE SHARE PURCHASE PLAN Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 332,044 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme NIL ORDINARY SHARES during period: Balance under scheme not yet issued/allotted at end 1,032,044 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt securities) originally listed and the date of admission: 1,000,000 ORDINARY SHARES OF 3 1/3p EACH ADMITTED 18 NOVEMBER 2002 700, 000 ORDINARY SHARES OF 3 1/3 p EACH ADMITTED 6 DECEMBER 2004 Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS ALL FIGURES HAVE BEEN REVISED FOR THE 3:1 SHARE SPLIT ON 11 MAY 2000 Name of company: SPIRENT PLC Name of scheme: NETCOM AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 5,986,513 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme during 1,207,333 ORDINARY SHARES period: Balance under scheme not yet issued/allotted at end 4,779,180 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 3,291,399 ORDINARY SHARES OF 3 1/3p EACH DATED 03/ securities) originally listed and the date of 09/1999 admission: 1,739,130 ORDINARY SHARES OF 3 1/3p EACH DATED 8 JULY 2002 6,722,689 ORDINARY SHARES OF 3 1/3p EACH DATED 8 OCTOBER 2002 Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter Fleming Way Crawley, RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: ZARAK AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 2,690,996 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme during NIL ORDINARY SHARES period: Balance under scheme not yet issued/allotted at end 2,690,996 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 3,895,474 ORDINARY SHARES OF 3 1/3p EACH securities) originally listed and the date of DATED 14 NOVEMBER 2000 admission: Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter Fleming Way Crawley, RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: SPIRENT SAVINGS RELATED SHARE OPTION SCHEME Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 186,355 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme during 5,543 ORDINARY SHARES period: Balance under scheme not yet issued/allotted at end 180,812 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 200,000 ORDINARY SHARES OF 3 1/3p EACH securities) originally listed and the date of DATED 31 DECEMBER 2003 admission: Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter Fleming Way Crawley, RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: SPIRENT STOCK INCENTIVE PLAN (FORMERLY KNOWN AS SPIRENT STOCK OPTION PLAN) Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 5,632,934 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme during 1,171,558 ORDINARY SHARES period: Balance under scheme not yet issued/allotted at end 4,461,376 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 3,720,930 ORDINARY SHARES OF 3 1/3p EACH securities) originally listed and the date of DATED 1 OCTOBER 2003 admission: 3,703,703 ORDINARY SHARES OF 3 1/3p EACH DATED 2 OCTOBER 2003 Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter Fleming Way Crawley, RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: SCHEDULE 5 BLOCK LISTING SIX MONTHLY RETURN To: Listing Applications UK Listing Authority Financial Services Authority 25 The North Colonnade Canary Wharf London E14 5HS Name of company: SPIRENT PLC Name of scheme: CAW AMENDED AND RESTATED STOCK OPTION PLAN Period of return: From: 1 JULY 2004 To: 31 DECEMBER 2004 Number and class of share(s) (amount of Stock/debt 929,607 ORDINARY SHARES OF 3 1/3p EACH security) not issued under scheme at end of the last period: Number of shares issued/allotted under scheme during 51,506 ORDINARY SHARES period: Balance under scheme not yet issued/allotted at end 878,101 ORDINARY SHARES of period: Number and class of share(s) (amount of stock/debt 1,300,000 ORDINARY SHARES OF 3 1/3p EACH securities) originally listed and the date of DATED 15 AUGUST 2002 admission: 115,394 ORDINARY SHARES OF 3 1/3p EACH DATED 28 AUGUST 2002 Please confirm total number of shares in issue at the end of the period in order for us to update our records 956,241,665 Contact for queries: Address: Spirent plc Name: Michael Anscombe Spirent House Telephone: 01293 767676 Crawley Business Quarter Fleming Way Crawley, RH10 9QL Person making return Name: Michael Anscombe Position: Assistant Company Secretary Signature: 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 07 January 2005 By ____/s/ Luke Thomas____ (Signature)*