The Unite general secretaryCredit:Telegraph Now union sources have told The Telegraph that Mr McCluskey’s latest attack on Labour MPs, accusing them of “dirty tricks” is a sign that he is worried about his position as union general secretary and knows that losing could damage Mr Corbyn. One source said: “Len is grasping at straws now, it’s clear that he is getting significant push back from members over his recent comments. “There are real concerns about the way Unite is being run, particularly the support for Momentum and the flat he bought. “He ought to be focused on those things, rather than thrashing out at people who have been members of the union for most of their working lives.” Gerard CoyneCredit:PA Tom Watson and Jeremy CorbynCredit:Eddie Mulholland Another added: “This is about shoring up the leader, in both senses. “Without Len, Corbyn is weakened and if he was ousted that could be the end of the left’s grip on our party. A lot of people would welcome that.” It came after Mr McCluskey told The Observer newspaper that MPs including Tom Watson, the deputy leader who Mr Corbyn publicly disagreed with over Syria last week, are “trying to abuse Unite’s democracy” to oust the Labour leader. Claiming that his election campaign has been turned into a third leadership race for Mr Corbyn by so-called hostile MPs, he said: “That is precisely what the media want it to be, and what the rightwing of the Labour party want it to be, and they have a puppet in Gerard Coyne that they can use.“Remember, those people who are running Coyne’s campaign are skilled masters of the dark arts. It is in their DNA and, though it is normal in political elections, it’s quite unique that they have brought this into a trade union election.”Mr McCluskey also named other Labour MPs, blaming them for running a “shameful campaign full of lies, innuendoes and smears” against him. John Spellar, MP for Warley, Jack Dromey, MP for Birmingham Erdington, and Siôn Simon, MEP for the West Midlands and Labour candidate for the West Midlands mayoral election were all named alongside Mr Watson. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. In a sign of the deep rift between the two men at the top of the parliamentary Labour party Mr McCluskey pointed spoke of his poor relationship with Mr Watson. He said: “We have not spoken since last July and it is sad that you lose friends but it is even sadder that Tom has turned on those of his friends who he relied upon in his darkest hours. He will have to answer to himself when he looks in the mirror every morning.”It came as John McDonnell, another close ally of the leader and the shadow chancellor, repeated claims that Mr Watson was wrong to support American missile strikes in Syria last week, exposing the disagreement at the heart of the party. Len McCluskey has been accused of “grasping at straws” after he claimed critics of Jeremy Corbyn are attempting to manipulate a union election battle to force him out of the top job and damage the party leader.The Unite general secretary is facing a challenge from Gerard Coyne, who he has accused of being backed by a “cabal” of MPs “fighting a proxy war against Corbyn” in what is being seen as a battle between moderate and left-wing factions of the party.Mr McCluskey, who has been at the top of the powerful union since 2011, is one of Mr Corbyn’s biggest and most powerful backers but he has been damaged by concerns about the way Unite supports pro-Corbyn group Momentum and about a flat he bought in London with the help of union money.He has demanded Labour investigate his claims after the election result has been announced on 21 April.