"I think it's a massive betrayal of the British people that he apparently does know the real risks of climate change," said Caroline Lucas, a Green Member of the European Parliament.

"His own scientific advisor said very clearly it represented a bigger threat than international terrorism, and he's refusing to put in place the policies to address that," she told a news conference.

The Green Party, which has members in the Scottish and European parliaments but none at Westminster, is fielding 200 candidates and targeting Labour voters disaffected by the war in Iraq.

Other groups have also criticised the main parties' track records.

A recent survey by Greenpeace took both Labour and the main opposition Conservatives to task for failing to live up to their rhetoric on the environment.

The survey rated the three parties' responses to 10 questions on climate change, with Labour coming out only one point ahead of the Conservatives on 38 percent and the Liberal Democrats the overall winner at 67 percent.

GREEN VOTE?

But although Blair has made climate change a key issue for his presidency of the Group of Eight rich nations and Britain's presidency of the European Union in the second half of this year, it has barely been mentioned in the election campaign.

"Who I give my vote to will be based on more immediate things like job security or whether I can afford to pay my mortgage," said James Edwards, a 33 year old Londoner who cycles to work every day.

"I cycle because public transport's depressing so although I'd vote on locally based green issues, like more cycle lanes, that's not how I'd choose my Prime Minister."

But the Greens' Lucas says it is time for the electorate to start thinking longer term.