LONDON (Bloomberg) — The UK government will sell about $2.56 billion ($5.1 billion) of shares in British Energy Group Plc to pay for the decommissioning costs of nuclear reactors owned by the country's biggest power generator.The sale of as many as 450 million shares will reduce the government's holding in the company to less than 39 percent from about 64 percent, the Department of Trade & Industry said yesterday in a Regulatory News Service statement. It will be the government's biggest stock sale since 1993, according to data compiled by Bloomberg.

Gordon Brown, the UK's chancellor of the exchequer and prime minister-in-waiting, said in March 2006 the government wanted to sell its stake in Livingston, Scotland-based British Energy. The government acquired its holding after rescuing the nuclear power generator from collapse in 2004. The company's shares have risen 40 percent from a 19-month low in February.

"The shares have been firming and they probably think now seems to be a good time to sell," Lakis Athanasiou, an analyst at Collins Stewart Ltd. in London, said yesterday in a telephone interview.

Shares of British Energy dropped 24.5 pence, or 4.3 percent, to 544.75 pence as of 2:11 p.m. in London, valuing the company at $3.14 billion pounds.

About 400 million shares of British Energy will be sold in an offering that will close at 4.30 p.m. local time today. A further 50 million shares may also be sold. The government has no plans to reduce its stake to less than 29.9 percent.