Len McCluskey, leader of the Unite trade union, entered Labour’s anti-Semitism row with a scathing attack on the party leader’s critics, accusing them of exploiting the scandal to weaken him.

Mr. McCluskey is head of the UK’s largest trade union and a key backer of Jeremy Corbyn, helping to get him elected.

He lashed out at the response of the Jewish community to the party’s ongoing crisis, accusing them of “refusing to take ‘yes’ for an answer”, as he listed a series of commitments made by Mr. Corbyn in tackling anti-Semitism.

Mr. McCluskey went on to bemoan the leadership of the Jewish community – the Board of Deputies, the Jewish Leadership Council and the Jewish Labour Movement before asking, “I therefore appeal to the leadership of the Jewish community to abandon their truculent hostility, engage in dialogue and dial down the rhetoric, before the political estrangement between them and the Labour party becomes entrenched.”

He warned in an article for HuffPost website that Labour risks plunging into a “vortex of McCarthyism” unless it ends the bitter row.

The hard left union leader insisted the Labour leadership have gone out of their way to try to address manifest concerns that the party harbours anti-Semites and Jew haters – drawing up a definition of anti-Semitism and speeding up disciplinary hearings for those accused of the racism.

He added: “What is the response from the leading Jewish community organisations to this record of reaching out, of understanding, and of action? Intransigent hostility and an utter refusal to engage in dialogue about building on what has been done and resolving outstanding difficulties.

“Indeed, the more Labour has addressed legitimate worries, the more Corbyn has personally sought to build bridges, the worse the rhetoric has become.”

Mr. McCluskey also accused three Jewish newspapers of “a thoroughly irresponsible act of fear-mongering” over a joint front page story accusing Mr. Corbyn of “an existential threat to Jewish life” in the UK, and said the the Board of Deputies of British Jews was guilty of “petulant trolling” after it claimed Mr Corbyn had gone “into hiding” over the summer.