Board of Deputies president Jonathan Arkush has launched a scathing attack on the controversial Jewdas group, suggesting they are a “source of virulent antisemitism” and claiming that their members “are not all Jewish”.

Mr Arkush appeared on Sky News on Tuesday lunchtime to discuss Jeremy Corbyn’s decision to attend a Seder organised by Jewdas previous evening.

But in remarks likely to cause further friction between mainstream Jewish organisations and those on the left, Mr Arkush said: “I just heard him (Jeremy Corbyn) describe antisemitism as vile and evil.

“So why then did he go to a group that is the source of virulent antisemitism and has dismissed the current news about antisemitism on the left as a right-wing smear.

“Either Jeremy Corbyn was deliberately provoking the Jewish community or making a catastrophic error of judgment. I don’t know which of these is true.”

Asked to comment on the fact that Jewdas consider itself to be a group of left-wing practising Jews, Mr Arkush added: “They are not all Jewish – but they are lifelong campaigners against the Jewish community to whom they show the upmost disregard and contempt.”

Mr Corbyn said the Jewdas Seder event on Monday evening was “very interesting” and involved “talking to a lot of young people about their experiences of modern Britain”.

Meanwhile in a her first statement to Labour members on Tuesday, the party’s new general secretary Jennie Formby expressed her determination to deal with the antisemitism crisis.

She wrote of “tackling problems in our own Party, above all in relation to antisemitism.”

Ms Formby added: “This week I will be moving to ensure the full implementation of the Chakrabarti report and introducing new procedures to deal with complaints and disciplinary cases.

“The stain of antisemitic attitudes must be completely eradicated within the Labour Party — we are the party for people of all races and faiths, the party of full equality for all, or we are nothing. Likewise, I will tackle any manifestation of misogyny, bullying or abuse of anyone, as Jeremy Corbyn has pledged.”

Meanwhile a tape of Mr Lansman, the founder of pro-Corbyn group Momentum, was obtained by the Evening Standard on Tuesday, in which he says many of the antisemitism cases being investigated by Labour were reported to the party by the Campaign Against Antisemitism group, which Mr Lansman dismisses as being “so right wing”.

The newspaper reports that Mr Lansman told a Momentum rally in Greenwich on March 26: “An awful lot of these cases that are brought to the attention of the Compliance Unit… are from an organisation called the Campaign Against Antisemitism, which is so right wing that it had a public spat with the Jewish Leadership Council.”