Labour has more than 200 cases of alleged antisemitic conduct from members still to be properly assessed or investigated, it has been claimed.
Party sources have suggested that 75 members are being investigated over alleged anti-Jewish behaviour.
But the Labour MP John Mann said he knew of 130 further cases that had not been dealt with properly and should now be reassessed.
The Jewish Leadership Council and Board of Deputies are among those known to be furious about the failure of Labour under Jeremy Corbyn to expedite investigations – with outstanding high profile cases including those of Ken Livingstone and Marc Wadsworth.
There has been an upsurge in antisemitic sentiment in the wake of Monday’s rally in Parliament Square organised by Jewish community organisations under the banner of “Enough Is Enough”.
A stream of antisemitic comments have been posted under an official Facebook post from Mr Corbyn in which he acknowledged the party had a problem with Jew-hate.
One wrote: “The only reason there’s bad press about Jeremy Corbyn is because he’s going against the global elite … the Jewish.”
Another stated: “Calling the Rothschild and other Jewish illuminati for what they are is not antisemitism.”
In a separate posting on the Labour Party Forum, an individual named as Steve Collier shared an article with American neo-Nazi origins entitled Elements of the Jewish Global Banking Mafia.
It wrongly lists numerous bankers as being Jewish – but has been widely circulated by the Ku Klux Klan in the United States.
One angry member of the Labour Party Forum described the post as “the worst case of antisemitism I have ever seen on the Labour Party Forum.
“Somebody, whose name is below, linked the most vilely antisemitic article I have ever had the misfortune of reading.”
At a meeting of Camden Labour Party in North London, Momentum activists voted on Tuesday night against including words from leader Mr Corbyn which aimed to strengthen a motion condemning antisemitism already passed by the party.
Joe Goldberg, one of two Jewish Labour councillors from Haringey to announce they were quitting the local authority after suffering widespread abuse, also revealed how the Tottenham Labour Facebook group had seen calls for MP David Lammy to be deselected because he attended Monday's demo to show solidarity with the Jewish community.
Meanwhile the pro-Corbyn blog The Skwawkbox began a campaign targeting Labour MPs who had attended Monday’s demonstration in Westminster and claimed they had failed to stand up against other forms of racism.
The 40 MPs who were sent an emailed message from the far-left blog demanding they answer questions on their commitment to anti-racism included Stella Creasy, who said: “This is not only divisive – it’s also fake.
“Whether it’s Ian Austin organising to visit lots of mosques in his constituency, Wes Streeting chairing the APPG on British Muslims, or me working with Tell Mama, this attack is clearly without any foundation.”
The Community Security Trust, which works on behalf of Jewish communities, said racism was “not a zero-sum game”.
“This attempt to bully and attack MPs who call out antisemitism is exactly the kind of ignorant, prejudicial support that Jeremy Corbyn and the Labour Party do not need, either right now or ever again in the future,” a spokesperson said.
“It is utterly pathetic and malicious. CST is proud of our relationships with Labour MPs, many of whom have consistently called out antisemitic discourse, and antisemitic incidents when they have occurred.”
It was also reported on Wednesday that a veteran hard-left activist accused of antisemitism was among pro-Corbyn demonstrators who organised a counter-protest at Monday’s Westminster rally.
Gerry Downing – who was expelled from Labour in March 2016 over a blog who wrote arguing that the 9/11 attackers should not be condemned – was among the 50 anti-Zionists to confront the main rally on Monday.
Also in attendance was Tony Greenstein, co-chair of the Labour Against The Witch Hunt group, who was expelled from Labour for abusive behaviour.
Elleanne Green, founder of the Palestine Live Facebook group which was found to have circulated antisemitic hate material following an investigation by campaigner David Collier, was also at Monday’s march.
Andy McDonald, Labour’s Shadow Transport Secretary, was also forced to clarify remarks made on Sky News at the weekend in which he talked about travelling to Auschwitz and the West Bank.
Joan Ryan, chair of Labour Friends of Israel, told Mr McDonald that “comparisons between Israel and Nazi Germany constituted a form of antisemitism”.
Mr McDonald insisted he was “trying to get across that he had taken in the enormity of two separate situations.”