Diane Abbott has accused her rival Labour leadership candidates of being "up to their necks" in the bitter feuds of New Labour.
Ms Abbott said her four opponents were either close to Tony Blair or Gordon Brown but were now distancing themselves from infighting and key policies like the Iraq invasion.
She branded the four former cabinet ministers "geeky young men in suits".
She also told the BBC a "wealth tax" was needed to tackle the deficit.
She and her rivals, David Miliband, Ed Miliband, Ed Balls and Andy Burnham, are taking part in hustings around the UK for the leadership contest - the outcome of which will be announced at September's conference.
In a hard-hitting interview with the BBC's Laura Kuenssberg, Ms Abbott - the UK's first female black MP - sought to distance herself from her rivals and their various allegiances during Labour's 13 years in power.
"You would not believe, to hear them, that they were at heart of new Labour project for at least a decade," she said.
"They were members of the Cabinet for the last five years. And yet, at hustings after hustings, they tell you 'they disagreed with this, they disagreed with that, they don't know why we did this, they don't know why we did that'.
"All this handwringing, and pretending they were not there and they were not at the heart of the project, that is slightly amazing."
She said she had been the most "consistent" of all the candidates on policy.
"I have not discovered in the past couple of months that I was against the Iraq war."
Labour had to move on from the era of Tony Blair and Gordon Brown and could not do so with a leader who was "up to their neck" in old battles.
Asked about claims that Mr Balls "briefed" against Tony Blair while he was prime minister - claims he has strongly denied - she said: "If Ed Balls says he was not involved, he was not involved. But it must have been his evil twin brother."
Ms Abbott, the only one of the four contenders never to have served in government, said she was best placed to "rebuild" Labour following its general election defeat because of the strength of her links to the party.
"I am the person to rebuild the party because I know it best. Because I have had a longer history and I was not fast-tracked or parachuted anywhere, I have worked my way up through the grass roots.
She denied she was intent on moving the party to the left.
"What new Labour did was that they worked the system and got the victories but we lost millions of voters," she said.
"I am talking about moving the party to where ordinary Labour supporters are. Ordinary Labour supporters are in a place where they want to see a party which they think is speaking for them and not the very wealthy."
She promised a "different approach" to tackle the crisis in the public finances from the other candidates, focusing equally on tax rises and spending cuts as a means of reducing the deficit.
As well as introducing a financial transaction tax and increasing the coalition's bank levy, she said she would create a new "wealth tax".
"I am working on the details of it but it would be a wealth tax directed at assets rather than income," she said.
She rejected suggestions she had little chance of winning the contest.
"I'm not comparing myself to Barack Obama because he's a once in a life-time figure but two years ago no-one could have imagined a black man as US President. If that was possible in the US, I think people can change their ideas in Britain as well."