People who are not members of the Labour party should register to vote in its leadership election so they can stop Jeremy Corbyn winning, Tony Blair’s former spin doctor has said.

Alastair Campbell, who served as New Labour’s director of communications from 1997 until 2003, claimed Mr Corbyn could destroy Labour if he became leader and said he had to be beaten.

“The madness of flirting with the idea of Corbyn as leader has to stop,” he wrote in a post on his blog. “That means no first preferences, no second preferences, no any preferences. It frankly means ABC, Anyone But Corbyn.

“Anyone who wants to see another Labour government one day should do what people who want a Corbyn leadership are doing – namely sign up as registered supporters for three quid in the next few days; but then I would hope they vote ABC.”

British Prime Minister Tony Blair, center, watched by his director of Communications and Strategy, Alastair Campbell, left (AP)

Mr Campbell is most notorious for his role in the preparation of the 2003 Iraq Dossier or so-called “dodgy dossier” that made the argument for Britain to invade Iraq.

Some Labour figures have previously criticised people signing up to vote in the contest and characterised them as “infiltrators”.

Mr Campbell also claimed that Mr Corbyn’s popularity was responsible for people rejecting the other candidates.

“One of the worst aspects of the so-called Corbynmania is that it is obscuring the solid decent abilities of the other candidates, who are each one of them better than most of the media will acknowledge, and far better equipped for the hard graft of detailed policy-making that has a chance of actually happening, so that we can make [change],” he argued.

Labour leadership: The Contenders Show all 4 1 /4 Labour leadership: The Contenders Labour leadership: The Contenders Jeremy Corbyn Jeremy Corbyn started off as the rank outsider in the race to replace Ed Miliband and admitted he was only standing to ensure the left of the party was given a voice in the contest. But the Islington North MP, who first entered Parliament in 1983, is now the firm favourite to be elected Labour leader on September 12 after a surge in left-wing supporters signing up for a vote. PA Labour leadership: The Contenders Liz Kendall Liz Kendall has been labelled the Blairite candidate throughout the contest, which partly explains why she has failed to attract the support needed in a party that has drifted even further from the centre-ground of British politics since the election. She has faced criticism over her relative lack of experience, having only served as an MP since 2010 and having no experience of ministerial or shadow cabinet roles. But that very lack of experience allowed her to initially make a pitch as the only candidate offering real change and a real break from the Blair/Brown/Miliband years, until Jeremy Corbyn entered the race and shifted the whole debate to the left. She is set to finish a disappointing fourth. PA Labour leadership: The Contenders Andy Burnham Andy Burnham started out as the front-runner in the leadership election, seen as the candidate of the left until Jeremy Corbyn entered the race. The former Cabinet minister has found himself squeezed between the growing populism of Corbyn’s radical agenda and the moderate, centre-left Yvette Cooper, not knowing which way to turn. It has attracted damaging labels such as ‘flip-flop Andy’, most notably over his response to the Government’s Welfare Bill. He remains hopeful he can win enough second preference votes to take him over the 50 per cent threshold ahead of Corbyn. PA Labour leadership: The Contenders Yvette Cooper.jpg Yvette Cooper has put her experience and achievements in government at the heart of her offer to the Labour party. She played a key part in setting up Sure Start in Tony Blair’s government and has pledged to continue her record on delivering for young families by promising a “revolution in the way families are supported” by introducing universal free childcare. She has also championed her role as a full-time working mother, taking pride in telling audiences that she does the school run for the kids before her day starts as a politician. But she has been criticised for being too wooden and lacking in passion and her attacks on Liz Kendall for “swallowing the Tory manifesto” at the start of the leadership contest have been criticised for helping Jeremy Corbyn brand all three mainstream candidates as ‘Tory-lite’. PA

A series of indicators including polls, local party nominations, and meeting attendance suggest that the left-winger is the favourite to succeed Ed Miliband to lead his party.

Mr Campbell is the latest New Labour figure to come out against Mr Corbyn.

Last month Tony Blair described the politics of the left-winger's supporters as "reactionary" and said anyone who believed in Mr Corbyn in their heart should "get a heart transplant".