Bookies have suspended betting on the date of the general election after a Cabinet minister appeared to let slip that it would be May 6.
Defence Secretary Bob Ainsworth said voters “will wake up and rue the day if they wind up with a Conservative government in charge of this country after May 6”.
A spokesman for Coral Bookmakers said: “It seems he's given the game away.”
But a spokesman for Mr Ainsworth said he had simply been “speculating” about the prospect of a Tory government.
The Defence Secretary told Sky News' Sunday Live: “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.”
A Coral spokesman said: “The month of May had been the odds-on favourite prior to Bob Ainsworth's comments on Sky News, and his mention of May 6 as the crucial date was enough for us to close the book.”