Former British Prime Minister Gordon Brown's attempts to hold on to power were thwarted by Nick Clegg's demand that he step aside as part of any coalition between Labour and the Liberal Democrats, it was reported today.
The Lib Dem leader informed the then prime minister to his face that a Lib-Lab alliance was only possible if Mr Brown bowed out.
According to Peter Mandelson's memoirs, serialised today in The Times, former British Prime Minister Tony Blair also told Mr Brown after May's inconclusive general election that the public would not accept him remaining in office.
After further calls for him to go from other senior Lib Dems, he announced he was resigning as Labour leader to allow coalition talks with the Lib Dems to continue. Ultimately the Lib Dems formed a coalition government with the Tories.
According to the account of Labour's coalition negotiations after the May 6 poll, Mr Brown went so far as drawing up a proposed Lib-Lab cabinet featuring Mr Clegg, Vince Cable and Paddy Ashdown as he plotted how to keep David Cameron out of Number 10.
But Mr Clegg, now the Deputy British Prime Minister, told Mr Brown that he had to quit if there was to be a deal between their two parties.
Mandelson records in his book 'The Third Man' that, at a meeting in the Prime Minister's Commons office on the Sunday after the election, Mr Clegg said: "Please understand I have no personal animosity whatsoever.
"But it is not possible to secure the legitimacy of a coalition and win a referendum unless you move on in a dignified way."
Mr Brown and Mandelson had used a secret tunnel between Number 10 and the Ministry of Defence to avoid attracting attention on their way to the meeting. Their car picked them up at the MoD to take them to Parliament.
The then prime minister is said to have avoided giving a straight response to Mr Clegg's ultimatum during the meeting, at which Danny Alexander - now the Chief Secretary to the Treasury - was also present.
It was not until the following day, after conversations with other Lib Dems and his predecessor Mr Blair, that Mr Brown resolved to resign.
According to Mandelson, Mr Blair backed the principle of a Lib-Lab coalition but told Mr Brown he could not be involved.
"Tony told him and me that the public would simply not accept Gordon remaining," he writes.
Mr Brown accepted that he had to quit but did not want to look like he had been forced out, it is said.
Mandelson quotes him as saying: "I have been humiliated enough."
The former business secretary also claims that Mr Brown eventually resigned as Prime Minister before the Tories and Lib Dems had finalised an agreement so that it was not dark as he left Downing Street for the last time.
Labour leadership candidate Ed Miliband told BBC Radio 4's 'Today' programme: "One of the lessons for Labour is that we do need to move on from some of the psychodramas of the past, some of the factionalism that there was.
"But I think there is a deeper lesson, which is that if any of us thinks we lost the election because of personalities, they are profoundly wrong.
"There are big issues for us to face up to about the fact that people lost a sense of who we were and what we believed. We began as the party of the windfall tax on privatised utilities and the minimum wage in 1997. We ended up - despite doing great things - as the party that was defending bankers' bonuses and pushing forward ID cards.
"I think there are profound lessons for us about how we make our values central to what we do."
Mr Miliband has been identified as a "Brownite", but pointed out that he had also worked with Mr Blair and insisted that he was "one of the people who actually tried to bridge some of the nonsense that there was and tried to stop some of the factionalism that there was".
He said: "I think there was too much factionalism. I always considered myself, and still do, one of the least tribal people in Labour politics and whoever wins this leadership election needs to realise that they need to be the leader of a party which uses all the talent at their disposal. That's certainly what I would do if I were leader."
Mr Miliband said Labour should be working now to bring down the Tory-Liberal Democrat coalition before the five-year period it has set for its first administration.
"I think there is a profound and real question for Liberal Democrat voters and MPs, because they didn't come into politics to put up VAT and hit some of the poorest people in our society," he said.
"The question is when are they going to wake up to that? I think the May elections next year are absolutely crucial to that. I was in Sheffield last week and I think Nick Clegg is going to get a real hiding in Sheffield, because people think he has started off his betrayal by betraying that city."