• Bob Ainsworth's aides dismissed poll date gaffe as 'speculation'
In a television interview yesterday, the Cabinet minister said voters "will wake up and rue the day if they wind up with a Conservative government in charge of this country after 6 May".
A spokesman for Mr Ainsworth said that he had simply been "speculating" about the prospect of a Tory government, but bookies yesterday suspended betting on the date.
The Defence Secretary said: "We are behind in the polls, but that election is far, far from decided yet, and as people begin to focus on the consequences of a Conservative government, Conservative policy and ability to take the decisions that the country needs to be taken, I think people are beginning to have some doubts about whether or not David Cameron is the right man.
"We haven't lost that election. We need to fight it. We need to fight it together with all our strength and ability and put that choice to the British public."
A spokesman for Coral Bookmakers said: "It seems he's given the game away."
Former Labour minister Tom Watson suggested that Mr Ainsworth would not have been privy to the Prime Minister's choice of election date.
He wrote on the microblogging site Twitter: "Bob's a good guy and all, but do you honestly think that he knows the date of the election?"
David Miliband, meanwhile, yesterday made clear that accusations that his party is indulging in "class war" will not force Labour to give up its portrayal of Mr Cameron's Tories as the party of privilege.
Speaking as opinion polls showed the Conservative lead over Labour dipping below ten points, the foreign secretary accused Mr Cameron of planning "the biggest redistribution of wealth to the wealthy in two generations".
Mr Miliband brushed off questions about his leadership ambitions, insisting he was "110 per cent" behind Gordon Brown, who he said would lead Labour into the general election in "three or four months' as the party of real change".
Labour should "pick up the gauntlet that the Tories have thrown down" with their Time For Change slogan, Mr Miliband said. "They say they want this to be an election about change – so do we. We want it to be an election about real change."
Labour's manifesto would look to the future by building on the party's achievements in bringing down crime, restraining the rise in unemployment during the recession and delivering improvements in the treatment of acute conditions in the NHS, he said.
And contrasting this package with the Conservatives' offer to the voters, he said: "What do they actually stand for? Abolishing inheritance tax, bringing back fox-hunting and isolating ourselves in Europe. That's not change. That's driving with one eye on the rear-view mirror."
Mr Miliband was widely suspected of wavering in his support for Mr Brown when former Cabinet colleagues Patricia Hewitt and Geoff Hoon issued an open letter calling for a secret ballot on the leadership.