Toshiba finalised the $5.4 billion acquisition of Westinghouse, the US nuclear reactor unit of British Nuclear Fuels, the British government subsidiary, in October after agreeing the deal in February.

The Japanese firm’s win of the tender with China, edging out French and Russian rivals after a two-year process, is likely to raise questions as to whether the British Government achieved value for money from the sale.

The cash deal was nearly three times the initial expected asking price for Westinghouse, but came just as the nuclear energy industry is enjoying a resurgence.

Westinghouse’s deal with China, which will create 5,500 jobs in America, is expected to smooth relations between Beijing and Washington, which have clashed recently over a range of issues from the yuan currency to the Chinese bid for US independent oil firm, Unocal.

Samuel W. Bodman, the US Secretary of Energy, said, after signing a protocol agreement in Beijing: “[The agreement] represents a major step forward in our relations and will advance our bilateral trade relationship and the energy security of both our nations,” Mr Bodman added that the deal would help America’s balance of payments with China, which hit a record $240 billion this year.

Beijing said that it had chosen the third-generation Westinghouse reactors over those of France’s Areva for technological reasons.

The contract will lead to the construction of four reactors, divided between Sanmen, in Zhejiang province, and Yangjiang, in Guangdong, and is part of the Chinese Government’s drive to increase its nuclear energy production.

Toshiba is already a big player in Japan’s nuclear power industry, having installed about a third of the nation’s nuclear generators.

The signing of the deal with China shows quick success for its strategy of using Westinghouse to help it to expand outside the saturated Japanese market into China and the US.

Toshiba has said that by 2015 it wants to triple its revenue from the nuclear power business.

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