Tony Blair described Gordon Brown as "mad, bad, and dangerous" as their relationship broke down over the contentious issue of the Labour leadership, Lord Mandelson has claimed.

Mr Blair described Mr Brown as "flawed, lacking perspective and having a paranoia about him", during their fractious relationship at the head of British politics, he claimed.

According to the former business secretary Mr Blair added that Mr Brown was "beyond hope of redemption".

The fraught nature of the Blair-Brown relationship has long been known but Lord Mandelson’s memoirs reveal for the first time the level of animosity felt between the two. Lord Mandelson disclosed that the then prime minister did promise the former chancellor in 2003 that he would step aside and not fight the next general election, a pledge he later reneged on.

At the same time, Mr Blair's advisers drew up plan "Operation Teddy Bear" to split the Treasury in two and weaken Mr Brown's power, it was claimed.

Lord Mandelson, whose memoirs The Third Man are being serialised in the Times, also revealed Mr Blair considered moving his rival to the Foreign Office but decided that the move may lead Mr Brown to resign and become a greater threat from the backbenches.

Mr Blair described Mr Brown as "like something out of the mafiosi". 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" he is alleged to have said.

Operation Teddy Bear was devised by Lord Mandelson, John Birt, the former BBC chief who became a Number 10 adviser, and Jonathan Powell, Mr Blair's chief of staff.

The plan was to take control of departmental spending away from the then chancellor. It would have created an Office of Budget and Delivery, leaving Mr Brown in charge of a new Ministry of Finance, the memoirs claim.

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