Exhibit 8.1

Principal Subsidiary Undertakings and Associated Undertakings

The following are the principal subsidiary undertakings and the associated undertakings ofeircomGroup as of
31 March 2004.

|Name                                                   |  | Proportion of Share Capital Held |   | Nature of Business                                                       |  | Registered Office and Country of Incorporation                      
|------------------------------------------------------ |  | -------------------------------- | - | ------------------------------------------------------------------------ |  | --------------------------------------------------------------------
|Principal Subsidiary Undertakings                     
|Valentia Telecommunications (unlimited public company) |  | 100                              | % | Holding company                                                          |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircomFunding (unlimited public company)               |  | 100                              | % | Financing company                                                        |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircomLimited                                          |  | 100                              | % | Provision of telecommunications and related services                     |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|Irish Telecommunications Investments Limited           |  | 100                              | % | Telecommunications financing and treasury management                     |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircom(U.S.) Limited                                   |  | 100                              | % | Marketing of telecom services in USA                                     |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|Osprey Property Limited                                |  | 100                              | % | Property Development Company                                             |  | Leitrim House,
Upper Stephen's Street,
Dublin 8.                    
|Eirtrade Services Limited                              |  | 100                              | % | Provision of electronic trading services                                 |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircomPhonewatch Limited                               |  | 100                              | % | Installation, monitoring and maintenance of residential security systems |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|Indigo Group Limited                                   |  | 100                              | % | Provision of internet services                                           |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircom(UK) Limited                                     |  | 100                              | % | Provision of telecommunications and related services                     |  | South Quay Plaza II,
183 Marsh Wall,
London E14 9SH,
United Kingdom.
|Lan Communications Limited                             |  | 100                              | % | Systems integrator                                                       |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircomInvestments BV                                   |  | 100                              | % | Investment holding company                                               |  | Strawinskylaan 3105 1077 ZX, Amsterdam, The Netherlands.            
|Eircable Limited                                       |  | 100                              | % | Investment holding company                                               |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|eircomHoldings Limited                                 |  | 100                              | % | Investment holding company                                               |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                    
|                                                       |  |                                  |   |                                                                          |  |                                                                     

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|Continuous Communications Systems Limited |  | 100 | % | Communications contractors                           |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                        
|----------------------------------------- |  | --- | - | ---------------------------------------------------- |  | ------------------------------------------------------------------------
|eircom(Infonet Ireland) Limited           |  | 100 | % | Provision of global data services                    |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                        
|GoFree Limited                            |  | 100 | % | Property investment company                          |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                        
|eircomNet BV                              |  | 100 | % | Investment holding company                           |  | Strawinskylaan 3105 1077 ZX, Amsterdam, The Netherlands.                
|eircomInternational Networks Limited      |  | 100 | % | Provision of telecommunications and related services |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                        
|Associated Undertakings                  
|eircomEnterprise Fund Limited             |  | 50  | % | Seed capital company and early stage fund company    |  | 114 St. Stephen's Green West, Dublin 2, Ireland.                        
|Beacon Integrated Solutions Limited       |  | 49  | % | Information technology consultancy                   |  | Howley's Quay,
Limerick, Ireland.                                       
|Telecom Engineering Services Limited      |  | 35  | % | Telecommunications engineering services              |  | Unit 14, Cherry Orchard Industrial Estate,
Dublin 10, Ireland.          
|Altion Limited                            |  | 33  | % | Telecommunications software solutions                |  | AIB Investment Building,
Percy Place,
Dublin 4, Ireland.                
|Buy4Now Limited                           |  | 22  | % | E-commerce software developer                        |  | 9 The Mall, Beacon Road, Sandyford Industrial Estate, Dublin 18, Ireland

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