JEREMY Corbyn is facing an Establishment plot to destabilise him, his close ally John McDonnell has claimed, as the party leader’s rival branded the Islington MP “delusional”.

Speaking at a TUC fringe event, the shadow chancellor told delegates: “To be clear, this is nothing to do with Jeremy Corbyn as an individual, this is about you. This is the Establishment saying to you: how dare you elect a socialist as a leader of the Labour party.”

He went on: “This is the one per cent telling the 99 per cent to get back in line; get back in your box. They want to get back to a politics that is simply a rotation of the political elites, cut off from the real world but dominated largely by the City of London and big finance and capital.”

Mr McDonnell added: “Sometimes we have to swim against the stream and stand up to vitriol. I know this sounds paranoid but some of this is organised by the Establishment to undermine us.”

He also told the BBC that the Corbyn campaign would “overcome the media barrage against us that's happening by using new techniques, social media, word of mouth meetings”.

The London MP added: “I was brought up a Roman Catholic, so I'm a great believer in the powers of conversion.”

In a BBC interview, Owen Smith, hotly tipped to lose the leadership contest when the result is announced on September 24, warned Labour would be "decimated" if there were a general election tomorrow.

When it was pointed out that Mr Corbyn had claimed he was building a "mass movement" capable of winning power while his allies suggested the Tories were now in retreat, the Pontypridd MP replied: “That's delusional and Jeremy needs to think a bit more about that straight, honest politics that he started his campaign with."

Mr Smith claimed the “straight, honest truth” was that Labour was presently at its lowest ebb ever in the polls. "If there was an election tomorrow Labour would be decimated, and that's got to be a shock to Labour's system," he declared.

The former shadow work and pensions secretary said Mr Corbyn was "misleading himself if he thinks we are heading towards an election victory".

If Labour continued on its current "disastrous trajectory", Mr Smith explained, it would be left with as few as 140 MPs; it currently has 230 with the Conservatives on 329.

Meantime, a member of Labour's ruling National Executive Committee suggested the party could use the massive shake-up in constituency boundaries to force out MPs who had been disloyal to Mr Corbyn.

Corbyn-supporting Darren Williams, who joined the NEC earlier this year, said that the process of choosing candidates to fight new or altered seats at the 2020 election - the number of constituencies is being reduced from 650 to 600 - would “present an opportunity for the selection of some new candidates who may be more in tune with the views of ordinary party members".

But shadow cabinet member Jon Ashworth insisted the process was "not about deselecting MPs" and that Mr Williams's comments did not represent "the position of Jeremy or his people".

Along with Mr Smith, whose Pontypridd seat is being merged with neighbouring Cynon Valley, Chuka Umunna, who represents Streatham in London, Yvette Cooper, the MP for Normanton, Pontefract and Castleford and Tristram Hunt, who represents Stoke-on-Trent Central, are among leading Labour moderates facing significant changes, which could leave them vulnerable to any de-selection attempt by hardline Corbyn supporters.