Shadow chancellor Ed Balls helped hatch a "brutal" plot, codenamed Project Volvo, to destroy Tony Blair after the 2005 General Election, according to leaked secret documents.
The Daily Telegraph claims Mr Balls, as well as Labour leader Ed Miliband, began scheming to divide their party within weeks of the election, around the time London was under attack from Islamic terrorists.
The paper says the documents show for the first time Gordon Brown's feelings towards Mr Blair in his own words.
It is claimed that in the cache of documents Mr Brown makes it clear, in a series of memos, that he regarded his rival as a "muddled" lightweight whose obsession with spin destroyed trust in politics.
Mr Brown reportedly ordered Mr Balls to take a "brutal" approach to cleanse the Labour Party of Mr Blair's influence.
The paper says the files show that Mr Balls was at the centre of a deal between Mr Brown and Mr Blair to let the Chancellor become Prime Minister.
In February 2006, the Telegraph reports, Mr Blair sent Mr Brown a secret unsigned letter setting out terms of a proposed deal.
The letter says: "You (understandably) want me to go now.
"You need to be the candidate of continuity and change. The second will be relatively easy to do. A different person is, by its nature, change. The first, however, rests on a smooth transition.
"Critical to that is not merely the absence of disunity in the handover; it is also the visible, clear demonstration that the person who most embodies NL [New Labour], ie me, is working hand in hand with the successor."
He suggests a five-point deal that includes Mr Brown leading on party reform. The pair would work together and Mr Blair would leave in summer 2007.
He ends with a warning: "Whilst I remain PM, the final decision has to be mine; and that cannot provoke a breakdown."
Mr Balls and Mr Brown responded by drawing up their own terms.
According to the files handed over to the Telegraph, the plot was codenamed Project Volvo, because that is the car seen as resembling Gordon Brown most.
Although people saw David Cameron as a "Sports car, BMW, they saw Brown as a Volvo, British Rover", according to one leaked presentation.
Volvos are generally seen as tough, safe and reliable - but maybe a little dull and high maintainence.