Milburn admits that Gordon Brown could lose the next election

Alan Milburn, the former health secretary, launched a thinly-veiled critique of the Prime Minister's leadership style as a raft of weekend surveys made grim reading for Downing Street.

The polls show the Conservatives are beginning to make a significant breakthrough, and that voters are not impressed by Chancellor Alistair Darling's first Budget or Labour's record on the economy.

Last night, Mr Milburn became the first Labour MP to voice his doubts in public about his party's chances as it seeks a fourth term.

In an interview for the website broadbandtvchannel. co.uk, the arch-Blairite and long-standing political enemy of Mr Brown said: "This next election will probably be the first since 1974 where the outcome is uncertain.

"I'm saying it is possible that Gordon Brown will not win the next election.

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"The issue for us is that we have lots of policies and lots of ideas, but can we encapsulate that in a clear vision of hope and optimism for the future? If we can, we can win the next election."

Although Mr Milburn said he believed a Labour win remained the most likely outcome, his willingness to raise the prospect of defeat will infuriate Mr Brown.

"The truth is if you go in for a fourth term you are asking people for 18 years and that's a big ask, so you really have to prove you have ownership of the future, never mind what's gone on in the past," Mr Milburn said.

Yesterday, a YouGov poll for the Sunday Times gave Labour its lowest rating since its days under former leader Michael Foot in 1983.

It put the party on just 27 per cent, a staggering 16 points behind the Conservatives on 43 per cent.

The Liberal Democrats were on 16 per cent.

If the results were to be repeated at the next General Election, it would be enough to sweep David Cameron to power with a landslide majority of 120 MPs.

A separate post-Budget poll by ICM for the News of the World put the Tories on 40 per cent, nine points ahead of Labour.

It also found that voters believe the Tories would do better with the economy, 34pc to Labour's 28pc.

Elsewhere, an ICM survey for the Sunday Telegraph suggests the public are depressed about the country's economic prospects.

Forty-four per cent believe that they will be worse off after tax rises on motoring and drinking in last week's Budget.