Conservatives have said Labour has sunk into "utter desperation" after two Cabinet ministers sent out signals to supporters to vote tactically for Liberal Democrats to keep David Cameron out of 10 Downing Street.

Prime Minister Gordon Brown played down the tactical voting message, telling GMTV: "I want people to vote Labour and I want a majority Labour government."

But Welsh Secretary Peter Hain said people should "vote with their heads, not their hearts" and recognise the "real fight" in their constituency, while Mr Brown's closest Cabinet ally Ed Balls acknowledged there is an "issue" in Lib Dem/Conservative marginals where Labour supporters want to keep out Conservatives.

The only Labour-supporting national newspaper, the Daily Mirror, has broken with a tradition stretching back generations by urging a tactical vote in 71 key marginal seats which could prevent "a Tory nightmare".

Campaigning in Hendon, Conservative leader David Cameron said: "What seems to be happening is that senior Labour politicians are saying, if you want to keep Gordon Brown in Downing Street, you need to vote Liberal Democrat.

"If you want, on Friday, a new government that rolls up its sleeves and starts to clear up the mess, you need to vote Conservative on Thursday."

Tory aides said the tactical voting call showed "utter desperation" and stood in stark contrast to Mr Cameron's "positive campaigning".

Shadow defence secretary Liam Fox said: "After 13 years, to have no positive reasons to give your own supporters to go out and vote for you smacks of political bankruptcy."

But Mr Hain countered that voters should "act intelligently in this election".

He said: "My ultimate aim is to get a Parliament which drives through political reform, with Labour in alliance with the Liberal Democrats and others who want to reform the political system from top to bottom. I think there's a natural progressive majority in the next Parliament if voters vote to get it."