Government officials say Blair will announce shortly a full-scale review to report back in 2006 and only then will a final decision be taken on whether to build new power stations.

"With some of the issues to do with climate change, and you can see it with the debate about nuclear power, there are going to be difficult and controversial decisions the government has got to take," Blair told a committee of senior parliamentarians.

"In the end it has got to do what it believes to be right in the long-term interests of the country," said Blair, who is believed to be in favour, in principle, of new nuclear build.

The government's chief scientific adviser, David King, urged Blair on Sunday to give the go-ahead for an expansion of nuclear power generation to help stem climate change.

The Confederation of British Industry has also pressed for a decision within a year to end uncertainty about energy supply.

Blair previously signalled a willingness to consider sanctioning new nuclear reactors to cut carbon dioxide emissions in his party conference speech two months ago.

All but one of the UK's nuclear power stations are due to close by 2023. Without new investment, nuclear power will contribute four percent of Britain's energy needs by 2010, down from 21 percent now.

Britain has become a net importer of gas and the government is more concerned about the security of its energy supply, which will increasingly come from abroad.

"The reason why we are coming back to that in the context of the energy review that we will announce shortly is that the facts have changed over the past couple of years," Blair said.

Trade and Industry Secretary Alan Johnson -- the lead cabinet minister on the issue -- may shed light on future plans when he testifies to a parliamentary committee on Britain's energy needs on Wednesday.

Johnson is expected to address the potential cost of new nuclear power stations and the industry's ability to deal with waste, while insisting that final decisions will depend on the outcome of the review.

Blair acknowledged he faced stiff opposition from environmentalists and parts of his Labour Party.

"About energy security and supply that will mean issues that are bound to be extremely controversial," he said.