David Miliband today dares Gordon Brown to sack him by setting out how Labour can still win the next election, in what is being seen as the launch of his leadership bid.

The Foreign Secretary fires the first salvo in a deliberate challenge to Mr Brown in a newspaper article that outlines a blueprint for defeating David Cameron without mentioning the Prime Minister once by name.

Although Mr Miliband said that he did not believe that Labour should indulge in “introspection”, he urged Labour MPs to “change the way we do politics” and “find the confidence” to make the new Labour case once again.

He makes clear that he blames Mr Brown for Labour’s shortcomings. Giving an unsparing critique of the party’s failings, he singles out delayed reform of the NHS and a failure to devolve power — two familiar complaints against the Prime Minister.

The article also fails to repeat the claim routinely made by other Cabinet ministers that Mr Brown is the best person to lead the country through the current economic turbulence. Mr Miliband instead carries the fight to Mr Cameron, accusing him of apeing “new Labour mark one . . . when the times demand a radical new phase”.

Using language that draws attention to his relative youth, he says: “The modernisation of the Labour Party means pursuing traditional goals in a modern way . . . new Labour won three elections by offering real change not just in policy but in the way we do politics. We must do so again.

“So let’s stop feeling sorry for ourselves, take a break, and then find the confidence to make our case afresh.” The article, in today’s Guardian, comes as the Foreign Secretary plans a series of speeches setting out his vision for the party’s future, according to an MP close to him. In doing so Mr Miliband will be effectively defying Mr Brown to sack him — a move that could hasten the Prime Minister’s own end.

Mr Miliband is likely to claim that he is doing no more than setting out his personal vision for Labour’s future, but the timing and content will ensure that the intervention is interpreted as an assault on Mr Brown’s leadership.

Labour whips are urging Mr Brown to bring forward his planned reshuffle after reports that ten ministers are prepared to stand down to force him to quit.

The momentum against Mr Brown picked up yesterday as ministers complained that he failed to restore morale after the Glasgow East by-election defeat with a lacklustre speech to the party’s national policy forum.

Mr Miliband has emerged as the strong favourite to replace Mr Brown in recent days after friends of James Purnell, the Work and Pensions Secretary, confirmed that he would not stand against him. An operation to canvass support for the Foreign Secretary is already under way among MPs and peers. Alan Johnson, the Health Secretary, is being lined up to serve as Mr Miliband’s deputy in a so-called “dream ticket”.

Harriet Harman, meanwhile, was at the centre of a row over the scale of her ambition after claims that she was twice heard to say, “This is my time”, as she watched footage of the Glasgow East defeat. The remark, which Ms Harman disputes, is said to have been made in the television and games room of the Radcliffe Building at Warwick University last Friday.

Aides to Labour’s deputy leader, who is “minding the shop” in Downing Street this week while Mr Brown is on holiday, denied the claims. “I am not preparing the ground for a leadership election,” Ms Harman. “I was bitterly disappointed by the Glasgow East by-election result in which I campaigned in support of Margaret Curran, a woman I admire greatly.”

Mr Miliband considered challenging Mr Brown for the leadership last year, urged on by close allies of Tony Blair. He reluctantly threw his weight behind the then Chancellor after being told that he lacked the necessary support among Labour MPs. Although the bookmakers’ favourite, Mr Miliband, 43, could also not be certain of winning sufficient backing from unions and activists.

In addition to likely rival campaigns from Ms Harman and others, Mr Miliband is almost certain to face a challenge from the Labour Left, which is convinced that the party’s future lies in abandoning the agenda associated with Mr Blair.

Downing Street claimed last night to be relaxed about Mr Miliband’s article and suggested that Mr Brown had been consulted in advance. Sources at No 10 acknowledged, however, that it may lead to “negative interpretations”.

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