Mounting excitement worldwide about prospects for atomic power stations has doubled the price that British Nuclear Fuels Ltd has been offered for its Westinghouse subsidiary and is set to propel British Energy into the FTSE 100.
Toshiba of Japan has put forward a $5bn (£2.8bn) offer for the US-based nuclear engineering group and the BNFL board is expected to formally agree a sale on Thursday, despite criticism in Britain.
Meanwhile, British Energy, the biggest nuclear power provider in the UK, will join the FTSE 100 index of leading shares on Thursday morning, replacing O2, which has been acquired by Telefónica.
Alan Johnson, the trade and industry secretary, was forced to defend the BNFL move at the launch of the government's own energy review, which could give the green light to new atomic plants in Britain.
"We took a long hard look at the issue. We decided now was the right time [to sell]. I think if we kept Westinghouse in public ownership and if we did go down the nuclear new-build route that would have created problems. If the government was the owner [of the company] that made the kit, that would have created competition problems," he explained.
"Westinghouse is currently putting four nuclear reactors in China. It's a very high-risk strategy. We don't think the taxpayer should be taking that risk. For those reasons, I think it's not the job of government to keep hold of Westinghouse. It is better for the UK to be getting a good price."
BNFL is in the middle of a wider sell-off, with proposals in front of Mr Johnson calling for him to agree the sale of another subsidiary, British Nuclear Group, which concentrates on the decommissioning and cleaning up of nuclear power stations.
Toshiba apparently beat off competition from its local rival Mitsubishi and General Electric Company of America to acquire the Pittsburgh-based Westinghouse, which BNFL bought in 1999.
A spokesman for the British group insisted that no final decision had yet been taken. "That process will take place at a board meeting this week," he added. But well-informed sources, who asked not to be named, told the Guardian that Toshiba had put in the winning bid.
The Japanese companies are keen to move out of their own nuclear market into faster-developing areas, such as China, which is pushing ahead with a raft of new-builds to meet galloping energy demand.
The decision has upset British critics who believe that the country might need Westinghouse's expertise in the event of the government giving the go-ahead - as expected - to build new reactors. A sale to Toshiba is also likely to attract strong opposition in Washington, where politicians including President George Bush have been lobbying to put Westinghouse under the control of a US firm such as General Electric.
Last night the trade union Prospect demanded that the sale meet strict public interest criteria, similar to those the union is seeking for the sale of the British Nuclear Group. Mike Graham, Prospect's national secretary, noted that the expected sale price was an "excellent return" on BNFL's original investment of $1.2bn and said Westinghouse employees felt they should benefit through a share issue.
When BNFL announced plans to sell Westinghouse last summer, industry experts had predicted that it would sell for just $2bn.