The true extent of the vicious internal feuding within the faction-riven new Labour government has been laid bare on the eve of the Labour Party conference.

Once close political allies, the relationship between former prime ministers Tony Blair and Gordon Brown grew increasingly acrimonious during the party's time in power, spilling over into open bitterness and hostility.

In extracts from a new memoir, published in the Daily Mail, Mr Brown's disgraced former spin doctor Damian McBride describes how he launched smear campaigns against Cabinet ministers during his boss's leadership bid.

Mr McBride confesses to leaking stories to the press about former home secretaries John Reid and Charles Clarke in a bid to ensure Mr Brown succeeded Tony Blair at Number 10.

Mr McBride said he acted "out of loyalty and devotion" for Mr Brown, and said that the then-chancellor was unaware of his Machiavellian attempts to discredit rivals.

He wrote: "Labour, Conservative or Liberal Democrat; Ministers, MPs or advisers; if they'd ever shared their secrets with colleagues in Westminster, the chances were that I ended up being told about them, too.

"I estimate I did nothing with 95 per cent of the stories I was told. But, yes, some of them ended up on the front pages of Sunday newspapers."

The publication came on top of a series of emails which have emerged recently, showing how Mr Blair's core team attempted to avoid endorsing Mr Brown as his successor in 2006.

The source of the emails, published by the Guardian, is Ben Wegg-Prosser, former director of strategic communications in Number 10.

They include discussions about which MPs could support Mr Blair, statements drafted for the prime minister, briefings to the media and the apparent frustrations of the PM.

The emails also refer to plans to find candidates to stand against Mr Brown in a leadership contest, including the possibility of persuading David Miliband to stand.

Former Labour Cabinet minister and arch-Blairite Tessa Jowell claimed that Ed Miliband, a close ally of Mr Brown, must have known about Mr McBride's smear campaign.