The election date is in the hands of the prime minister
A Cabinet minister has fuelled speculation the general election will take place on 6 May.
Defence Secretary Bob Ainsworth told Sky News the public will "rue the day if they wind up with a Conservative government... after the 6 May".
He is not the first minister to suggest inadvertently that the poll, which must be held by 3 June, will happen then.
6 May is seen as the most likely date but Labour sources said Mr Ainsworth had been talking "speculatively".
It is widely assumed that Gordon Brown will call the election for 6 May, the same day on which council elections are being held.
Mr Brown said recently there would be a Budget in the spring, which experts said would effectively rule out an election in March or April.
'Rue the day'
Speaking about the upcoming election campaign, Mr Ainsworth said it was "far from decided" despite the fact Labour is lagging behind the Conservatives in the opinion polls.
"As we begin to focus on consequences of a Tory government, people are beginning to have some doubts about whether David Cameron is the right man," he said.
"We haven't lost the election. We need to fight it together with all our strengths and ability and put that choice to the British public because I think they will wake up and rue the day if they wind up with a Conservative government in charge of this country after 6 May."
Health Secretary Andy Burnham was accused of "letting the cat out of the bag" last month about the timing of the election when he spoke of the importance of getting legislation outlawing the unsupervised use of sun beds passed by May - only to correct himself.
Pre-election campaigning has already begun with all the main parties publishing draft details of policies in certain areas.
The Conservatives and Lib Dems both say they are on an election footing as a poll could be called at any time.