Jeremy Corbyn is facing fresh criticism from Labour MPs after attending a Passover gathering of a radical left-wing group called Jewdas, which recently described the antisemitism row as a “faux-outrage greased with hypocrisy and opportunism”.

It comes as the Labour’s new general secretary, Jennie Formby, starts her first day in the role with a brief to improve the party’s handling of allegations of antisemitism.

Mr Corbyn insisted on Sunday evening that “absolutely strong and watertight” investigations would be take place where allegations occur, adding: “We are not tolerating antisemitism in any form in the Labour Party”.

But the Labour leader was embroiled in the new row after the Guido Fawkes website reported that Mr Corbyn had attended the event hosted by Jewdas to mark the Jewish feast day of Seder.

After organising demonstrations outside Parliament last week against antisemitism in the party, the Jewish Board of Deputies, Jewish Leadership Council and Jewish Labour Movement, were accused by Jewdas in a statement at the time of “playing a dangerous game with people’s lives”.

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Allegations linking Mr Corbyn to antisemitism were “the work of cynical manipulations by people whose express loyalty is to the Conservative Party and the right wing of the Labour Party”, it said.

“It is a malicious ploy to remove the leader of the opposition and put a stop to the possibility of a socialist government.”

Commenting on the Labour leader’s attendance a spokesman for Mr Corbyn said: “Jeremy was invited to a Passover Seder with Jewish members of his local community.

“He wrote to the Board of Deputies of and Jewish Leadership Council last week to ask for an urgent meeting to discuss tackling antisemitism in the Labour Party and in society.“

But the Campaign Against Antisemitism described Mr Corbyn's attendance as “a very clear two fingered salute at mainstream British Jewry”.

Campaign chairman Gideon Falter said: “Given the anti-Semitism crisis engulfing the Labour Party, there is absolutely no way that Mr Corbyn can claim that this too was an oversight.

“It is hard to imagine how this duplicitous man can claim to be remedying anti-Semitism within the Labour Party. The party must consider the message that is sent to British Jews and other minorities by him remaining as leader.”

Labour backbencher John Woodcock said Mr Corbyn's attendance at the meeting was “irresponsible and dangerous”.

“This is deliberately baiting the mainstream Jewish community days after they pleaded with him to tackle antisemitism,” he wrote on Twitter. “And he must know that meeting them now will give his members the message that the group's extreme views are ok.”

And the Labour MP Wes Streeting told Guido Fawkes: “What on earth was he thinking? This demonstrates either extraordinarily bad judgement or a deliberate affront to the majority of British Jews. Probably both.

“It calls into serious question the sincerity of every public statement Jeremy Corbyn has made on antisemitism during the past week, just as many of us hoped we had begun to make progress.“

Jewdas shrugged off the attack, posting a Twitter message: “Great that there's so much interest in our work tonight! Please feel free to make a donation!”

Protests against Labour antisemitism Show all 14 1 /14 Protests against Labour antisemitism Protests against Labour antisemitism Protesters clashed during the demonstration Reuters Protests against Labour antisemitism Members of the Jewish community hold a protest against Labour party leader Jeremy Corbyn and antisemitism in the Labour Party AFP/Getty Protests against Labour antisemitism Protesters hold placards and flags during a demonstration, organised by the British Board of Jewish Deputies for those who oppose antisemitism, in Parliament Square Reuters Protests against Labour antisemitism Hundreds of people gathered in Parliament Square to protest against antisemitism in the Labour Party EPA Protests against Labour antisemitism Labour MP Luciana Berger speaks during the protest PA Protests against Labour antisemitism A protester blows through a shofar during the demonstration Getty Protests against Labour antisemitism Members of London's Jewish community protest in support of Labour leader Jeremy Corbyn outside parliament EPA Protests against Labour antisemitism Labour MP John Mann speaks during a protest against antisemitism PA Protests against Labour antisemitism People protest against antisemitism in the Labour Party as Jewish community leaders have launched a scathing attack on Jeremy Corbyn, claiming he has sided with antisemites ‘again and again’ PA Protests against Labour antisemitism Labour politicians Stella Creasy and Chuka Umunna leave after attending the demonstration Getty Protests against Labour antisemitism A pro-Jeremy Corbyn protester holds a placard during a counter-protest Getty Protests against Labour antisemitism A support of the Labour Party hold up a placard during the demonstration Reuters Protests against Labour antisemitism Jeremy Corbyn supporters during the demo Reuters Protests against Labour antisemitism A protester holds up a sign reading ‘For the many, not the Jew’ AFP

The group said: “We are proud to be Jews and proud of everyone who attended, whether they were Jewish or not.

“We want everyone to know - we're leaving Mitzrayim (Egypt). Change is coming. Revolution will come.”

Referring to Jewdas, David Baddiel, a Jewish comedian, posted on his social media account: “They are just Jews who disagree with other Jews. Which means: Jews.“

The Momentum founder, Jon Lansman told BBC Radio 4’s Today programme that it was Mr Corbyn’s “night off”, adding: “He had nothing official in his diary, his office didn’t know he was there. So I don’t think this is as significant as it’s being made out.

He added: "Well it's certainly not helpful to Jeremy or the cause of opposing anti-Semitism in the Labour Party as it happens... and I think the important thing is that Jeremy is seeking to meet with mainstream Jewish organisations. He wants to meet, he's very keen to meet and has been since before the demonstration last Monday with the Board of Deputies and the Jewish Leadership Council.“