Ed Miliband has been forced to deny any involvement in attempts to smear opponents amid claims that "damaging" emails could have been sent by him to one of the key figures in a plot to attack senior Tories.
The potential link between the Labour leader and Derek Draper, who was behind a proposed Labour-supporting political gossip website, is among the latest allegations in a memoir from Gordon Brown's former spin doctor.
In his memoirs, Damien McBride said the Labour leader “might have problems” if his exchanges with Derek Draper were revealed.
Mr McBride claims he asked Mr Draper: “What’s the worst anyone could have found if they’ve been in your emails?”
In the latest extracts from Mr McBride's memoir Power Trip, being serialised in the Daily Mail, the former member of the Brown inner circle suggests Mr Miliband could "have problems" if any emails to Mr Draper became public.
Reigniting the turmoil of the Blair-Brown era, the controversial revelations threaten to overshadow the Labour Party conference despite Mr Miliband's efforts to seize the initiative by announcing he would scrap the "bedroom tax" if he wins the 2015 general election.
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Labour sources denied that Mr Miliband had any involvement in the proposed websiteRed Rag, which ultimately brought about the downfall of Mr McBride, and the book does not suggest he was involved.
Mr McBride was forced to resign in 2009 when it emerged he sent Mr Draper emails containing unfounded smears about Tory MPs for the website.
A spokesman for Mr Miliband said: "Ed was not involved in any plan to smear or spread lies about opponents. Any suggestion he was is totally untrue."
Mr Draper said there were a number of Labour ministers "who would have problems because of things they've written to me".
Mr McBride said the names given by Mr Draper were: "Peter Mandelson - definitely, James Purnell - definitely and Ed Miliband - probably."
Mr Miliband has now come under pressure to reveal what he knew about the systematic campaigns Mr Brown's former spin doctor has admitted orchestrating to destroy the careers of Labour rivals during the bitter infighting of the New Labour years.
he has been accused of knowing about the “vile” smear operation conducted by senior aides in the last Labour government, a former Cabinet minister said.
Ardent Blairite Dame Tessa Jowell told BBC News she found the revelations “truly shocking”.
She said Mr Miliband – then Mr Brown’s close ally – must have known what was going on. And she feared the “awful, evil influence of people like Damian McBride” would destroy the last government’s reputation.
She added: "I don't think it's damaging for Ed Miliband. I'm sure he knew that this was going on. He was actually away a lot of the time.
"But the strength of Ed Miliband has been to say that that is the past, we are not going back to that and that I am not going to preside over a parliamentary party or a Labour party that allows this kind of bad and malign behaviour and I think that has been a very important part of building confidence."
But Conservative MP Henry Smith called for transparency from the Labour leader.
"After the revelations from Tessa Jowell, Ed Miliband must now tell us what he knew about McBride's Labour smear campaigns," he said.