'You're a F****** A*******!': Labour civil war explodes behind the scenes of BBC's Question Time as John McDonnell and Alastair Campbell almost come to BLOWS

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John McDonnell and Alastair Campbell had a furious row after clashing on BBC Question Times and almost came to blows, it has been claimed.

The shadow chancellor and Tony Blair's veteran former spin chief were embroiled in angry exchanges on the BBC debate programme.

But eye witnesses have suggested the row escalated further after the cameras stopped rolling as Mr McDonnell is alleged to have branded his rival a 'f****** a*******'. 

The row exploded the bitter civil war that is devastating the Labour Party as Jeremy Corbyn clings to his job as party leader with the backing of members but without the support of almost all his MPs. 

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Mr McDonnell was also involved in bruising clashes with former Downing Street spin doctor Alastair Campbell, pictured right

Mr Campbell said he feared Mr McDonnell and Jeremy Corbyn were leading the party to 'disaster' during the bitter exchanges

A source told The Sun that Mr Campbell asked why Mr McDonnell had got so personal as they rowed on air and raged: 'You and your lot are going to ruin the Labour Party' prompting the four-letter outburst.

Onlookers said Mr Campbell's daughter had to calm things down.

A source said: 'It was very heated. Nobody knew where to look.'

Mr McDonnell's spokesman denied he had sworn despite multiple witnesses saying he did.

The aide said: 'It didn't happen, John just ignored Alastair when he was shouting at him, which seemed to wind him up more.'

During the show, Mr McDonnell was also involved in an extraordinary spat with former minister Anna Soubry over claims female politicians are being 'terrorised' by left-wing activists.

The Tory branded the shadow chancellor a 'nasty piece of work' as she said that one Jewish Labour MP was living in a safe house due to abuse from left-wing activists. 

Shadow chancellor John McDonnell, left, was branded a 'nasty piece of work' by Tory former minister Anna Soubry on Question Time

Some of the most ferocious exchanges came as Mrs Soubry took him to task for trying to deny that he was a Marxist.

The Broxtowe MP pointed out that there was a video on YouTube where he described himself as a Marxist. 

And she went on: 'I tell you something else Mr McDonnell, you are a very nasty piece of work.

'There are colleagues of mine in House of Commons, Labour MPs, who are at the point of being terrorised by McDonnell and his cronies.

'There are women MPs who suffer day in, day out from misogynist, unpleasant, sexist abuse on Twitter, Facebook - from people who are apparently within their own party.

'There is a Jewish Labour MP - a woman - who is living in a safe house because of the level of anti-Semitism she has to bear.'

Mrs Soubry said one Jewish Labour MP was living in a safe house following abuse from left-wing activists

Ms Soubry said some MPs were 'so frightened, humiliated, almost terrorised by Mr McDonnell and his gang they will leave politics'.

Turning to McDonnell she told him: 'You sir can stop it.'

But Mr McDonnell dismissed Mrs Soubry's 'abuse' of him as 'outrageous'.

He said the Labour leadership had made clear it condemned any abuse of MPs. 

'We are not accepting this smear campaign that is going on from the Tories and others as well,' Mr McDonnell said.

Tempers boiled over again when Mr Campbell - a key figure in Tony Blair's three general election victories - warned that veteran left-wingers Mr McDonnell and Jeremy Corbyn were leading the party to 'disaster'.

Mr McDonnell interrupted to say: 'It's nauseating because you are the one, above all else, who actually created the environment where no one believed a word a politician said.

'You lost us five million votes in that process and set us up to fail. The reason Jeremy was elected is because people want some honesty back in politics again.'

Mr Campbell responded: 'Oh my God.'

Earlier Mr Campbell had conceded that there were 'issues' from the Blair years that had been damaging to Labour - including the Iraq War and tuition fees.

But the two Labour figures soon lost patience with each other.

Mr Campbell accused Mr McDonnell and his allies of 'destroying' the party. 

'And what's more, I actually worry you don't even care,' he added.

At one point Mr Campbell lamented about being unable to keep the discussion civil.

 'I came on here tonight to be as nice to you as I possibly can,' he said.

Mr McDonnell broke in: 'The feeling is mutual.'

Host David Dimbleby struggled to control the heated discussion on the show, which was filmed in Salisbury last night

The audience gasped as Mrs Soubry took Mr McDonnell to task over activists' behaviour