With Britain's ageing plants set to be retired in the coming years, David King told the BBC "we have to take decisions very quickly."

Nuclear power meets more than a fifth of Britain's energy needs but that will fall to just four percent by 2010 if reactors built in the 1960s and 1970s are not replaced soon.

Blair relaunched the nuclear debate in September by saying all options were being considered in a review of the government's energy policy, but he faces stiff opposition from green groups and some in his Labour Party to building new reactors.

But faced with the reality of global warming, King said "the equation is simple".

The declining share of energy produced from nuclear reactors -- a carbon dioxide-free source -- was contributing to the failure to meet the government's targets for reducing emissions by 2010.

"I think we need every tool in the bag to tackle this problem," King told the BBC.

But Environment Minister Margaret Beckett said it would be impossible to build nuclear reactors quickly enough to help Britain meet its targets under the Kyoto treaty, which requires nations to cut greenhouse gases.

There were concerns about the full cost of nuclear power and storage of waste, but climate change meant governments had to take another look at nuclear energy, she told the BBC.

"I've always accepted we can't afford to close the door on nuclear," Beckett said.

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