Exhibit 8.1

|Subsidiaries as of June 1, 2006                                                                                                                    |  | Country of
Incorporation |  | Trading
Name          
|-------------------------------------------------------------------------------------------------------------------------------------------------- |  | ------------------------ |  | ----------------------
|Communications
Performance Analysis division                                                                                                       |  |                          |  |                       
|Spirent Communications Inc:
    Calabasas, California, USA
    Eatontown, New Jersey, USA
    Honolulu, Hawaii, USA
    Sunnyvale, California, USA |  | Delaware, USA            |  | Spirent Communications
|Spirent Communications of Ottawa Ltd                                                                                                               |  | Canada                   |  | Spirent Communications
|Spirent Communications (SW) Ltd                                                                                                                    |  | England                  |  | Spirent Communications
|Spirent Communications (India) Pvt Limited                                                                                                         |  | India                    |  | Spirent Communications
|Spirent Communications (Asia) Limited                                                                                                              |  | Hong Kong                |  | Spirent Communications
|Spirent Communications Technology (Beijing) Limited*                                                                                               |  | PRC                      |  | Spirent Communications
|QuadTex Systems, Inc.                                                                                                                              |  | Texas, USA               |  | QuadTex               
|SwissQual Holding AG                                                                                                                               |  | Switzerland              |  | SwissQual             
|Service Assurance division                                                                                                                         |  |                          |  |                       
|Spirent Communications of Rockville, Inc.                                                                                                          |  | Delaware, USA            |  | Spirent Communications
|Spirent Communications (International) Ltd.*                                                                                                       |  | England                  |  | Spirent Communications
|Spirent Communications Ltd                                                                                                                         |  | England                  |  | Spirent Communications
|Spirent Communications (Scotland) Ltd*                                                                                                             |  | England                  |  | Spirent Communications
|Systems                                                                                                                                            |  |                          |  |                       
|PG Drives Technology Ltd                                                                                                                           |  | England                  |  | PG Drives Technology  
|PG Drives Technology Inc                                                                                                                           |  | Delaware, USA            |  | PG Drives Technology  
|Financial                                                                                                                                          |  |                          |  |                       
|Spirent BV                                                                                                                                         |  | The Netherlands          |  | Non-Trading           
|Spirent Holdings Corporation                                                                                                                       |  | Delaware, USA            |  | Non-Trading           

This
list of subsidiaries omits certain subsidiaries that, in the aggregate, would not be a "significant subsidiary" as of December 31, 2005. All shareholdings in the companies
are held indirectly by Spirent Communications plc, except where indicated by an asterisk (*) where the shareholding is held directly by Spirent Communications plc.

---