|   | **Exhibit 12.1** |
|--------|------------------|

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**CERTIFICATION PURSUANT TO****18 U.S.C. SECTION 1350****AS ADOPTED PURSUANT TO****SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002**

In connection with the Annual Report of mmO2 plc (the “Company”) on Form 20-F for the period ending March 31, 2003, to be filed with the Securities and Exchange Commission on 7 July 2003 (the “Report”), the undersigned hereby certify that to the best of our knowledge:

| 1. | The Report fully complies with the requirements of Section 13(a) of the Securities Exchange Act of 1934; and |
|----|--------------------------------------------------------------------------------------------------------------|

|   |                                                                                                                                                 |
|--------|------------------------------------------------------------------------------------------------------------------------------------------------------|
| 2.     | The information contained in the Report fairly presents, in all material respects, the financial condition and results of operations of the Company. |

|   |
|--------|

|   | /s/ Peter Erskine      ————————————— |
|--------|-------------------------------------------------------------------------------------------------------|
|   |                                                                                                  |
|   | Name: Peter Erskine                                                                                   |

|   |                           |
|--------|--------------------------------|
|   | Title: Chief Executive Officer |

|                     |   |
|--------------------------|--------|
| Date:        7 July 2003 |

|   |
|--------|

|   | /s/ David Finch      ————————————— |
|--------|-----------------------------------------------------------------------------------------------------|
|   |                                                                                                |
|   | Name: David Finch                                                                                   |

|   |                           |
|--------|--------------------------------|
|   | Title: Chief Financial Officer |

|                     |   |
|--------------------------|--------|
| Date:        7 July 2003 |

|                                                                                                                                                                                                                                                    |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
|  A        signed original of this written statement required by Section 906 has        been provided to mmO2 plc and will be retained by mmO2        plc and furnished to the Securities and Exchange Commission or its staff        upon request. |

|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| In        accordance with the interim guidance for Section 906 certification issued        by the United States Securities and Exchange Commission on March 21, 2003        in Release No. 33-8212, this certification will not be deemed “filed”        for purposes of Section 18 of the Securities Exchange Act of 1934, or        otherwise subject to the liability of that section. Such certification        will not be deemed to be incorporated by reference into any filing under        the Securities Act of 1933 or the Securities Exchange Act of 1934, except        to the extent that mmO2 plc specifically incorporates it by        reference. |

 

 

 

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