Focusing on the future of the environment yesterday, the prime minister refused to rule out building new nuclear power stations.

Tony Blair said in a keynote speech on climate change that the government's position had not changed from last year's energy white paper, which kept the option open.

But the Department of Trade and Industry denied reports that its own research suggested nuclear was necessary, insisting a leaked document was simply an options paper which had not been approved.

Blair promised to make tackling climate change the focus of the UK's G8 presidency next year.

But he doubted whether the position of the US Senate had changed on the issue of reducing greenhouse gas emissions, since it rejected the Kyoto treaty in 1997.