Battering for Brown as Cameron polls 52%

The Mori poll had Labour trailing on a dismal 24 per cent - some 28 points behind and facing wipe-out at a general election.

It was the best Conservative showing since the heyday of Margaret Thatcher and showed Mr Cameron taking votes from both Labour and Nick Clegg's Liberal Democrats, who were down four points to 12 per cent.

It came as former Cabinet minister Alan Milburn urged Labour to embrace "change" - taken by MPs as a coded pitch for a leadership contest. "The willingness to change is what has made New Labour so dominant in British politics and forced even our most strident opponents into contemplating changes they once thought abhorrent," he wrote in an article for the Blairite group Progress. "Now change beckons once again." He criticised the "splurge of Whitehall initiatives" and urged greater "clarity".

There were more claims that Gordon Brown's authority was being weakened by criticism of his leadership, including fresh leaks from Tuesday's political Cabinet meeting.

Communities Secretary Hazel Blears was identified as the minister who asked why the Cabinet was focusing on perceived chinks in the Tory armour rather than on Labour's own weaknesses.

One member was quoted in the Guardian as saying the tenor of the discussion was "bizarre and a denial of reality as we sat listening to how deep down David Cameron is not really popular".

Another said it was "a dreadful misjudgment" to dwell on the Conservatives and seemed complacent.

Yesterday's Standard disclosed the dissent at the meeting and that the Commons aide to Business Secretary John Hutton, Eric Joyce, is planning to resign in order to speak out against Mr Brown.

Work and Pensions Secretary James Purnell raised eyebrows in an interview today saying that it would be "ridiculous" to criticise rebels worried about Labour's plunging poll ratings. He admitted he shared their concern.

Today's Mori survey found 54 per cent agreed that Mr Cameron's party was ready to form the next government - up by 19 points since last month.

Three quarters were dissatisfied with the way Labour was running the country and two thirds were unhappy with Mr Brown's performance.

But there was scepticism about both parties. Voters thought Labour more likely than the Tories to "promise anything to win votes", by a margin of 40 per cent to 36 per cent.

Meanwhile there was speculation among MPs today that Mr Brown might call a "back me or sack me" leadership contest if the party loses the Glenrothes by-election.

Asked on GMTV if he should take the step, Home Secretary Jacqui Smith replied: "No."

She denied that ministers were plotting against the leadership, adding: "What matters to me when I get up in the morning is thinking what am I going to do today to help the British people feel safer on the streets."