Peter Mandelson has publicly disowned Gordon Brown's "class war" strategy by warning that people should not be judged by "how well off they are".
The Secretary of State for Business and First Secretary of State also suggested he had helped to save the Labour Party by returning to Mr Brown's Cabinet in 2008 and insisted a "lack of ambition" barred him from seeking the Labour leadership.
Predicting that the outcome of this year's election would be close, he claimed Labour was neither a "write-off" nor "dead certs to win".
In an interview in next month's Esquire, Lord Mandelson undermined the plan pursued in some quarters of Downing Street to attack David Cameron, George Osborne and Boris Johnson over their public schooling.
The peer's comments will do little to quell speculation of a rift between him and the Prime Minister over election strategy. The pair have been working closely together on the campaign, but Lord Mandelson is said to have had concerns about the crackdown on bankers' bonuses and other measures targeting the wealthy in last month's Pre-Budget Report.
Lord Mandelson's remarks in Esquire are his first public comments on the "class war" strategy.
He was asked whether his attendance at a shooting weekend with the Rothschild family and Colonel Gaddafi's son Saif – though Lord Mandelson did not take part in the shoot – would play well with Labour voters. He replied: "How do you know they don't vote Labour? It depends what you think the world is. If it's a world of privilege and indifference to the rest of society, then I would not be seen dead in it. I judge people not by how well off they are, but by their values."
Lord Mandelson's comments underscore how the Cabinet is split over waging a class war. Mr Brown triggered alarm among some ministers when he said last month that the Tories' inheritance tax breaks for millionaires was "dreamed up on the playing fields of Eton".
In a ComRes poll for The Independent on Sunday last month, seven out of 10 voters said the fact that Mr Cameron had been educated at Eton would not make him a bad Prime Minister.
The headmaster of Eton College yesterday said he was dismayed that his school was being used as a political football in the coming election.
In an interview with The Independent, Tony Little said the £9,617-a-term school provided places for boys from a variety of backgrounds, adding that "one might have hoped" the strategy was a thing of the past.
Despite the criticism, Mr Brown has failed to draw back completely from the strategy. In his New Year message, the Prime Minister, referring to the Conservatives, said: "There are some who say we must plan for a decade of austerity and unfairness, where the majority lose out while the privileged few protect themselves."
Ed Balls, in an interview with The Times last week, said: "This idea we are fighting a class war is a nonsense, but we will not pull back from attacking the Conservatives as the party of privilege and the rich."
But Jack Straw has distanced himself from the strategy by insisting that people have "little choice over where they go to school".
In his interview, Lord Mandelson claimed that "the further we travel from the intervention in Iraq, the more people are able to see the sense of it". This remark will raise eyebrows as the Chilcot inquiry into Iraq is throwing up more, not fewer, doubts over the case for war.
Lord Mandelson was asked why he thought Mr Brown recalled him to the Cabinet in October 2008. He said: "He brought me back for two reasons. First, to help the Government through the worst financial crisis we've seen in a generation. Second, to bring some stability to the party, which was going through a rough time and needed some welding together."
He predicted that the 2010 election would be "midway" between 1987, when Labour had no chance of winning, and 1997, when a Labour landslide was on the cards. "We're not a write-off, nor are we dead certs to win," he said.
He denied that he had saved Mr Brown's job last June when the resignation of James Purnell, the Work and Pensions Secretary, nearly triggered a full-scale coup, but claimed he had been a "calming hand". He said "I don't expect" there will be another challenge to Mr Brown before the election.
Lord Mandelson played down suggestions he could succeed Mr Brown, despite the possibility that legislation could be introduced to allow life peers to give up the peerage so he could stand as an MP. He said: "Apart from my lack of ambition, there is something else standing in the way, quite a big thing. The life peerage. You can't divest yourself of it."
Full interview appears in the February issue of 'Esquire', on sale 7 January