<PAGE>   1
Exhibit 12.1
CALCULATION OF EARNINGS TO FIXED CHARGES RATIO SUCCESSOR COMPANY


EXCLUDING THE RESULTS OF THE GENERATION BUSINESS

<TABLE>
<CAPTION>
                                                                 Nine Month       Year
                                          Year Ended           Period Ended      Ended
                                         December 31,          December 31,  March 31,
                                                2000                  1999        1999
                                             (pound)         $     (pound)     (pound)
                                                      (Amounts in millions)

<S>                                       <C>           <C>         <C>        <C>
Earnings
Pretax income from continuing operations          73        109         47         62
Adjustments to include distributed income
  of less than 50% owned persons                 --         --         --         --
Add: Amortization charge on capitalized
  interest                                       --         --         --         --
Less: Interest capitalized in the period         --         --         --         --
                                                 ---        ---        ---        ---
Total earnings before fixed charges               73        109         47         62
                                                 ===        ===        ===        ===
Fixed charges
Interest expense                                 116        173         87        126
Interest capitalized                             --         --         --         --
                                                 ---        ---        ---        ---
Total fixed charges                              116        173         87        126
                                                 ===        ===        ===        ===
Total earnings and fixed charges                 189        282        134        188
                                                 ===        ===        ===        ===
Ratio of earnings/fixed charges                  1.6        1.6        1.5        1.4
                                                 ===        ===        ===        ===
</TABLE>

INCLUDING THE RESULTS OF THE GENERATION BUSINESS
<TABLE>
<CAPTION>
                                                                 Nine Month       Year
                                          Year Ended           Period Ended      Ended
                                         December 31,          December 31,  March 31,
                                                2000                  1999        1999
                                             (pound)         $     (pound)     (pound)
                                                      (Amounts in millions)
<S>                                       <C>           <C>         <C>        <C>
Earnings
Pretax income from operations                     73        109         47         68
Adjustments to include distributed income
  of less than 50% owned persons                 --         --         --         --
Add: Amortization charge on capitalized

  interest                                       --         --         --         --
Less: Interest capitalized in the period         --         --         --         --
                                                 ---        ---        ---        ---
Total earnings before fixed charges               73        109         47         68
                                                 ===        ===        ===        ===
Fixed charges
Interest expense                                 116        173         87        129
Interest capitalized                             --         --         --         --
                                                 ---        ---        ---        ---
Total fixed charges                              116        173         87        129
                                                 ===        ===        ===        ===
Total earnings and fixed charges                 189        282        134        197
                                                 ===        ===        ===        ===
Ratio of earnings/fixed charges                  1.6        1.6        1.5        1.5
                                                 ===        ===        ===        ===
</TABLE>