Exhibit 8.1

|                                                                                                         |                                                                                                        | Country of Incorporation |  | Trading Name          
|-------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------ | ------------------------ |  | ----------------------
|Communications
Performance Analysis division                                                             |                                                                                                        |                          |  |                       
|Spirent Communications Inc:                                                                              |                                                                                                        | Delaware, USA            |  | Spirent Communications
|                                                                                                         | Calabasas, California, USA
Eatontown, New Jersey, USA
Honolulu, Hawaii, USA
Sunnyvale, California, USA |                          |  |                       
|Spirent Communications of Ottawa Ltd                                                                     |                                                                                                        | Canada                   |  | Spirent Communications
|Spirent Communications (SW) Ltd                                                                          |                                                                                                        | England                  |  | Spirent Communications
|Service Assurance division                                                                               |                                                                                                        |                          |  |                       
|Spirent Communications of Rockville, Inc.                                                                |                                                                                                        | Delaware, USA            |  | Spirent Communications
|Spirent Communications Ltd                                                                               |                                                                                                        | England                  |  | Spirent Communications
|Spirent Communications (Scotland) Ltd*                                                                   |                                                                                                        | England                  |  | Spirent Communications
|Network Products                                                                                         |                                                                                                        |                          |  |                       
|Trading divisions of Spirent plc:                                                                        |                                                                                                        |                          |  | HellermannTyton       
|HellermannTyton:
    Aldridge, West Midlands, UK
    Plymouth, Devon, UK
    Wythenshawe, Manchester, UK |                                                                                                        |                          |  |                       
|HellermannTyton (Pty) Ltd                                                                                |                                                                                                        | South Africa             |  | HellermannTyton       
|HellermannTyton S.A.                                                                                     |                                                                                                        | France                   |  | HellermannTyton       
|HellermannTyton AB                                                                                       |                                                                                                        | Sweden                   |  | HellermannTyton       
|HellermannTyton GmbH                                                                                     |                                                                                                        | Austria                  |  | HellermannTyton       
|HellermannTyton GmbH                                                                                     |                                                                                                        | Germany                  |  | HellermannTyton       
|HellermannTyton Ltda                                                                                     |                                                                                                        | Brazil                   |  | HellermannTyton       
|HellermannTyton Pte Ltd                                                                                  |                                                                                                        | Singapore                |  | HellermannTyton       
|HellermannTyton Data Ltd                                                                                 |                                                                                                        | England                  |  | HellermannTyton       
|HellermannTyton Corporation                                                                              |                                                                                                        | Delaware, USA            |  | HellermannTyton       
|Tyton Company of Japan Ltd (Associate)                                                                   |                                                                                                        | Japan                    |  | HellermannTyton       
|Systems                                                                                                  |                                                                                                        |                          |  |                       
|PG Drives Technology Ltd                                                                                 |                                                                                                        | England                  |  | PG Drives Technology  
|PG Drives Technology Inc                                                                                 |                                                                                                        | Delaware, USA            |  | PG Drives Technology  
|Spirent Systems San Diego Inc                                                                            |                                                                                                        | Delaware, USA            |  | Spirent Systems       
|WPDS Software Ltd                                                                                        |                                                                                                        | England                  |  | Spirent Systems       
|Financial                                                                                                |                                                                                                        |                          |  |                       
|Spirent BV                                                                                               |                                                                                                        | The Netherlands          |  | Non-Trading           
|Spirent GmbH                                                                                             |                                                                                                        | Germany                  |  | 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, 2003.

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