David Cameron has been rebuffed by the Liberal Democrats after appealing for a "progressive alliance" to be formed to challenge Gordon Brown.
The Tory leader's move, ahead of tomorrow's Liberal Democrat leadership election result, backfired when it was ridiculed by senior party figures.
His offer of co-operation will fuel speculation he is trying to prepare the ground for a possible anti-Labour coalition government in the event of a hung parliament after the next election.
Mr Cameron said: "I've always believed that political parties, even though they may have serious disagreements over many aspects of policy, should work together in areas where they agree. So I hope that in 2008 the Liberal Democrats and the Green Party will join us in putting pressure on the government to decentralise power, and that together we can create a new progressive alliance to decentralise British politics."
Mr Cameron appeared to be reaching out to Nick Clegg and Chris Huhne, who have fought a close contest for the Liberal Democrat crown.
Vince Cable, the party's outgoing acting leader, said it would continue to work with others where they shared common ground. But he added: "This not a serious proposal and David Cameron clearly lives in cloud cuckoo land. A Conservative party that wants to cut funding on public services and talks the talk on green issues but fails to deliver any meaningful policies has little to offer today's Britain."
Mr Huhne said: "David Cameron's claims to be pushing the green agenda are just as hollow as Gordon Brown's."
The former leader, Charles Kennedy, also dismissed the idea, citing Tory hostility to closer ties with the EU. He said: "I don't somehow see the basis of a great progressive consensus."
Mr Clegg is expected to win a narrow victory in the party leadership contest when the result of the vote of 64,000 Lib Dem members is announced tomorrow. He has been the frontrunner throughout the contest that followed Sir Menzies Campbell's resignation in October. But Mr Huhne has run an effective campaign and the margin between the men is likely to be close. Whoever wins will be keen to distance himself from Mr Cameron in an effort to carve out distinctive political territory.
Caroline Lucas, the Greens' principal speaker, said: "There's a huge gulf between what David Cameron says and what the Tories are doing."
Mr Cameron's move reflects growing confidence in Tory headquarters. It was underlined by an opinion poll yesterday that gave the party a commanding lead. The YouGov survey for The Sunday Times put the Tories on 45 per cent (up four), Labour on 32 per cent (down three) and the Lib Dems on 14 per cent (up one).
David Miliband, the Foreign Secretary, denied the Government was in crisis after a turbulent month. He said: "It doesn't feel like meltdown at all. It is the job of headlines to come up with the drama. It is the job of government to do serious business."Reuse content