The challenger for the post of general secretary of Unite, Britain’s biggest trade union, Gerard Coyne, has issued a furious denunciation of both Ken Livingstone and the two panellists on the Livingstone hearing who are members of Unite.

Mr Coyne described Livingstone’s comments “and total lack of contrition” as “grotesque”.

But in response to suggestions that the two Unite representatives on the Labour National Constitution Committee panel, Russell Cartwright and Brenda Warrington, “had argued against having a hearing”, Mr Coyne told Jewish News: “I am ashamed that representatives of my union on the NCC panel were allegedly arguing against having any hearing at all”.

And, in a reference to the role of other Unite members at Labour’s disputes committee, considering allegations of antisemitism at the Oxford University Labour Club, Mr Coyne said: “The leadership of Unite seems to think its role in the Labour Party is to defend the indefensible”.

He added: “There is a troubling trend of racism within the labour movement at the moment. I had to report to the police anti-Semitic comments and images tweeted at me last month.

“We need to stamp this out. If a member of Unite acted in the way Mr Livingstone has, under my leadership they would be expelled.”

Police are understood still to be investigating a series of tweets and images, said to be antisemitic, sent to Mr Coyne on social media by someone identifying themselves only as “1UnionBloke”.

On March 17, the person tweeting under that name sent a message to Mr Coyne, which said: “Following advice I unreservedly apologise for any offence caused to you by recent tweets and will be de-activating this account”.

To date, according to Mr Coyne’s office, police have not yet established who was responsible for the tweets, but according to the Guido Fawkes political website, some Unite officials believe the former accountholder to have been “a senior official in the Unite union”. Other tweets from the account are said to have included internal union documents which Unite sources say would only be available to serving, high-ranking officials in the union.

Asked earlier on Wednesday morning about the decision to suspend Livingstone rather than expel him a spokesperson for Unite, said: “This is a matter for the Labour party, not Unite, so we will not be making any comment. As you know, in recent weeks we have had to say more than once, unfortunately, that we do not want outside interference in our democracy, so best we practise what we preach”.

Last year McCluskey insisted that there “was no crisis of antisemitism in the Labour Party” and said he believed that “this is nothing more than a cynical attempt to manipulate antisemitism for political aims”.

Questions have now emerged over how two members of the same union, Unite, came to sit on the panel for the Livingstone hearing. Russell Cartwright is the secretary of the parliamentary staff branch of Unite, while Brenda Warrington is a Tameside councillor and long-standing member of Unite. The panel chair, Rose Burley, is a member of Walsall South constituency Labour party (CLP) and is branch secretary of her local GMB union. She has been a Labour Party member for more than 50 years. All three, who sit on the 11-member National Constitution Committee, would have been asked to make themselves available for the hearing.

Cartwright has been identified by the Labour MP John Mann as an active member of the “Scoop It’ website, which allows members to “curate” — that is, post material which interests them — from a variety of world media sources. Cartwright’s two areas of interest are Palestine and music. He is also understood to be a member of the activist group the Campaign for Labour Party Democracy, which has close links with the hard-left Momentum organisation.Momentum, in turn, is an aggressive backer of Len McCluskey’s campaign to remain general secretary of Unite.