Tony Blair branded Gordon Brown "mad, bad, dangerous and beyond redemption" as their long-standing leadership feud reached boiling point, according to Peter Mandelson.
In the latest instalment of his memoirs, serialised in The Times, the former business secretary said that, under pressure from Mr Brown, Mr Blair agreed in 2003 not to fight the next general election, only to renege on his promise.
Lord Mandelson also describes how he and other No 10 aides drew up a secret plan - codenamed Operation Teddy Bear - to split the Treasury, breaking up Mr Brown's powerbase in government.
On two other occasions Mr Blair was said to have considered moving Mr Brown from the Treasury to the Foreign Office - but each time drew back fearing that he would resign and pose an even greater threat from the backbenches.
Lord Mandelson describes in graphic terms the deterioration in relations between the two men at the heart of New Labour, with Mr Blair accusing his then chancellor of behaving like a mafia boss.
Mr Blair was quoted as saying that even the then deputy prime minister John Prescott was "scared" by Mr Brown. "He knows there's something wrong with him," he said.
Lord Mandelson said Mr Blair described Mr Brown as "flawed, lacking perspective and having a paranoia about him".
In early 2005, after Mr Blair finally went back on his promise not to lead Labour into the general election, Lord Mandelson said that Mr Brown came to him to demand that he finally gave an exit date.
Mr Blair was quoted as saying: "He's like something out of the mafiosi. He's aggressive, brutal ... there is no one to match Gordon for someone who articulates high principles while practising the lowest skulduggery."
Lord Mandelson said that Mr Blair "variously believed, and told me, that Gordon was mad, bad, dangerous and beyond hope of redemption".
The bitterness continued after Labour's 2005 election victory, with Lord Mandelson relating how Mr Blair described one meeting he had with Mr Brown to discuss pension reform.
"It was the ugliest meeting he had ever had .. I have never been confronted with such ugliness in my life. It was a naked, undisguised threat," Lord Mandelson writes.
Lord Mandelson also describes how in 2001 Mr Brown's venom was directed against him. He said that Mr Brown was furious when an official report cleared him of wrongdoing in the Hinduja passport affair.
He said that Mr Blair told him: "Gordon wants you buried. That's what he wanted from the Hammond report. He was very angry with the outcome."
But despite the constant pressure from Mr Brown to stand aside, Lord Mandelson said that Mr Blair was determined to fight on as prime minister.
"He's thinking of only one thing. Only of removing me, but I am not going to be pushed out." Mr Blair was quoted as saying.
Lord Mandelson describes how, together with former BBC director general John Birt and No 10 chief of staff Jonathan Powell, he secretly devised the plans for Operation Teddy Bear.
Under the scheme a US-style office of budget and delivery would have been taken out of the Treasury, leaving Mr Brown in charge of a new ministry of finance handling taxation, markets and financial services.
Crucially, however, Mr Brown would have lost control of departmental purse strings which enabled him to wield such power within the government.
Labour leadership contender Andy Burnham said it was time for the party to move on from the feuding of the Blair-Brown era.
He told the BBC Radio 4 Today programme: "I think it's time for a new generation in the Labour Party to go forward, hold the floor and set out our views for the future of the Labour Party.
"These revelations really go to the heart of why I'm standing. We really need a clean break from this kind of politics."
Asked about Mr Blair's supposed view of Mr Brown, the former Health Secretary, who served under both men, said: "I don't recognise that description."
Mr Burnham added: "This is what Labour's got to leave behind, this indulgence. I don't think it helps the party to rake over all these coals."Reuse content