Labour's battle of the brothers gets personal

David Miliband will today make his strongest criticism of his younger brother Ed with the Labour leadership contest getting personal as it reaches a critical stage.

The former foreign secretary will suggest his brother is pandering to Labour's core vote rather than reaching out to the middle classes and that his strategy will keep the party in opposition rather than return it to power.

David Miliband will set out clear dividing lines between him and his brother, seen as the two front-runners in the race to succeed Gordon Brown. Ballot papers will be sent out next week and the result announced on 25 September.

The shadow Foreign Secretary will say that Labour must be an alternative government as well as an effective Opposition. "Opposition is necessary but insufficient. At worst it can take us back into our comfort zone – and our pantomime role in politics," he will say. "We need not just to oppose this Government. We need to defeat them."

David Miliband will insist that he is the best candidate to prevent the Government painting his party as Old Labour. "We need to break out of the mould the Coalition is trying to put us in," he will say. "Their attacks on our record are only the first phase of their campaign. They seek to make Labour irrelevant. I will not let them."

He will say that Labour's leadership contest has spent, "a lot of time looking inwards and backwards, when we need to look outwards and forwards". He will pledge to look "outside our tent" and talk about the change that Britain, rather than the party, needs.

Calling on Labour to shift to the centre ground, he will say: "We must look forwards for new ideas and outwards for a new coalition of voters..

"We are pigeonholed as spendthrift when we need to be prudent; we are seen as accreting power to the state when in fact our mission is to empower individuals, communities and businesses; and we are seen as the establishment when we need to be the insurgents." Yesterday he won the support of his 100th Labour MP.

Ed Miliband, the shadow Energy and Climate Change Secretary, moved to head off his brother's criticism by insisting he is "the moderniser". He said that, since 1997, Labour had lost 1.7 million middle-class voters. But he argued that Labour had lost a total of 5 million voters, with the largest losses amongst the C2, and D and E social classes.

Ed Miliband said: "I am the only candidate who can reach out to those whom we have lost.

"To those middle-class voters who have switched to the Lib Dems I say look at how Labour is changing."

Contenders go negative...

David Miliband on Ed Miliband:

"If I thought Ed would be a better leader than me, I'd be running his campaign."

Ed Miliband to David Miliband:

"I think it [the Iraq war] has been profoundly damaging to Britain, David, and I disagree with you on that."

Diane Abbott on Ed Balls

"If Ed Balls says he was not involved [in Brown-Blair infighting]... it must have been his evil twin brother."

Ed Balls on the Miliband brothers:

"Yvette [Cooper, his wife] and I decided it would have been weird [to run against each other as the Milibands have]. I don't think we really needed to talk about it."

Diane Abbott on the Milibands:

"We're not going to be able to engage with society and, particularly, engage young people in politics, if they see the political class as a caste apart, a strange sort of geeky young men in suits."

Andy Burnham on the Milibands:

"I didn't have well-connected parents. People are looking for politicians who have real-life experience."