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".
