A fierce debate over nuclear power is under way after Tony Blair launched an energy review which could pave the way for a new generation of nuclear plants.
Mr Blair says there is "feverish rethinking" over energy policy
Greenpeace protesters disrupted Mr Blair's speech and other green groups voiced anger that nuclear could be used to fill gaps in energy supplies.
But business groups have welcomed the review, saying a clear decision on future supplies and nuclear is needed.
Ministers say they have so far made no decisions on building new plants.
That is despite reports that Mr Blair has been convinced that building more nuclear power stations is the only way to meet energy needs and stick to the targets on climate change.
Mr Blair had to make his speech in a different hall after the protesters climbed into the roof at the Business Design Centre in Islington, London.
He said nuclear power was a difficult issue but should be settled by open debate, not protests to stop free speech.
The energy review would be headed by the Energy Minister Malcolm Wicks and report by the middle of next year, he announced.
It would measure the UK's progress against a review carried out two years ago.
And it would "include specifically the issue of whether we facilitate the development of a new generation of nuclear power stations", he said.
Mr Blair said energy policy was "back on the agenda with a vengeance".
"Energy prices have risen. Energy supply is under threat. Climate change is producing a sense of urgency."
He warned that "by around 2020 the UK is likely to have seen decommissioning of coal and nuclear plants that together generate over 30% of today's electricity supply".
"Some of this will be replaced by renewables, but not all of it can," he argued.
The last energy review was in 2003 but since then ministers say Britain has moved from being self-sufficient in gas to being a gas importer.
Mr Wicks said his review would look at nuclear power along with renewables, coal, gas and new technologies.
It will also cover energy efficiency and cutting carbon emissions from transport.
Some Labour MPs are already voicing their opposition to any new nuclear plants.
Ex-Environment Minister Michael Meacher said they were not necessary and said the nuclear option had almost been ruled out in a government review in 2003.
"What has really happened in the last two-and-a-half years is the government has twiddled its thumbs and not promoted renewables in the way that it said it would," he said.
'Nuclear tax' fear
Roger Higman, from Friends of the Earth, said nuclear was expensive, produced radioactive waste and as a technology could not be exported because some countries wanted to built nuclear weapons.
Liberal Democrat leader Charles Kennedy warned that it had cost £56bn to clean up existing UK nuclear plants.
He accused the government of making no assessment of the cost of building new plants and said a new "nuclear tax" was likely.
But business leaders, who are worried about the possibility of energy sources for big users this winter, welcomed the review.
They said a quick decision was needed to help them plan for the future.
Sir Digby Jones, director-general of the Confederation of British Industry, said: "If this nation, the fourth biggest economy on earth, is going to play a full role in the 21st Century, we have got to stop hesitating."
And Keith Parker, from the Nuclear Industry Association, said he hoped the review would produce a serious and well-informed debate.
Conservative shadow energy minister Bernard Jenkin said the review was long overdue and urged ministers to keep an open mind.
"If nuclear is efficient, let industry and the private sector finance it, if it's not efficient, then it won't happen," said Mr Jenkin.