ELECTRICITE de France SA, the world's biggest operator of atomic-power plants, may pay too much for British Energy Group Plc by raising its 12-billion-pound (US$21.5 billion) offer.

British Energy, the United Kingdom's biggest power producer, is worth no more than 777 pence a share in a takeover, 1.6 percent above the 765-pence offer level, because the French company may face delays in building new plants needed to make the purchase profitable, says Ingo Becker, an analyst at Landsbanki Kepler, Bloomberg News reported.

Morgan Stanley analyst Bobby Chada values the shares at 665 pence, including 50 pence for new plants. "Soaring build costs and potential shortages in both equipment and engineers" would make a higher bid risky, according to Becker, who is based in Frankfurt.

An acquirer "would not be willing to pay up significantly for optional site value," he said in a September 10 investor note.

The biggest risk to British Energy shareholders may be that EDF abandons its offer after failing with its July 31 approach.

The East Kilbride, Scotland-based company has traded within 9 percent of EDF's offer since August 1, indicating the market is still betting on a deal.

EDF has dropped 13 percent since then while energy prices slumped and equities fell. The UK utility's biggest private shareholders said the bid undervalued its eight nuclear stations and adjacent land where more reactors may be built.

Becker said any revised bid for the company, which is 36 percent state-owned, is unlikely to exceed 800 pence.

British Energy's land is attractive to Paris-based EDF, which has plans for at least four new UK reactors from 2017.

British Prime Minister Gordon Brown supports the expansion of nuclear power to replace older plants.