Nick Clegg has said the Liberal Democrats would support whichever party gained the most MPs in the event of a hung parliament.
Speaking on the BBC's Sunday AM programme the Liberal Democrat leader said whichever party received the "strongest mandate" from the electorate would have earned the right to seek power.
"Whichever party have the strongest mandate from the British people, it seems to me obvious in a democracy they have the first right to seek to try and govern, either on their own or with others," he said.
A hung parliament could present a huge opportunity to the Liberal Democrats, who would hope to use their position as king-makers to secure a deal on electoral reform.
But while Labour is far more receptive to changing the electoral system than the Conservatives, Clegg would be anxious to avoid propping up an unpopular Gordon Brown.
David Cameron told the same programme that he did not believe the election was a "shoo-in or a foregone conclusion."
"I think the state of the nation's opinion is that people are disillusioned with Labour, with the government, they are disillusioned also with politics, but they are not going to just hand it over to the Conservatives," He said.
"We have got to work for it and earn it. I have got to work for it and earn it."
Their comments come as an Ipsos MORI poll for the Observer showed the Tory lead had been slashed to 37 per cent - just six points ahead of Labour.
If repeated at a general election Cameron would be denied an overall Commons majority.
Labour are likely to be buoyed by the figures, which show the gap between the two main parties is the narrowest it has been for a year.
But Gordon Brown will have been disappointed by Clegg's comments as they appearsto scupper any chance of a Lib-Lab pact that would keep him in Downing Street.
Cameron also rejected suggestions made by his shadow business secretary Ken Clarke that an outright Labour victory would be better than a hung parliament.
He said: "I think frankly anything is better than another five years of this Labour government.
"But I am working night and day, not for a hung parliament, but for a majority government - because I do think that in Britain today we have got to take tough and difficult decisions. I would rather have a government that can do that."
