Jeremy Corbyn is facing fresh criticism over his failure to tackle anti-Semitism in Labour following a report that the party has a backlog of 74 cases that are still to be dealt with.
A Labour source quoted by the Daily Mail said some of the cases dated back two years and included some of the "most shocking and blatant" examples of anti-Jewish sentiment.
The party insisted that the number of "live" cases represented no more than 0.01% of the Labour membership.
A spokesman said that any complaints of anti-Semitism were dealt with "extremely seriously" and were fully investigated.
However, the disclosure is likely to increase the pressure on Mr Corbyn, who acknowledged on Monday that the party had been "too slow" in dealing with cases of anti-Semitism and apologised for the "hurt" it had caused.
His admission followed an unprecedented letter from the Board of Deputies of British Jews and the Jewish Leadership Council accusing him of siding with anti-Semites "again and again".
The Mail quoted a Labour source as saying: "Many of these case include the most shocking and blatant anti-Semitism that would make even a committed Nazi blush.
"From Holocaust denial to outright hatred of Jewish people these views should not be tolerated anywhere in society let alone Jeremy Corbyn's Labour Party."
In response to the claims, a Labour Party spokesman said: "The Labour Party is committed to challenging and campaigning against anti-Semitism in all its forms.
"Any complaints of anti-Semitism are taken extremely seriously. These are fully investigated in line with our rules and procedures and any appropriate disciplinary action taken."
Party sources said that in the case of "severe" allegations, members were immediately suspended pending investigation.
They also pointed out that the party leader did not oversee the complaints procedure which was handled by the governance and legal unit overseen by the general secretary.
Meanwhile, Labour MPs Wes Streeting, co-chairman of the All Party Parliamentary Group on British Jews, and John Mann, chairman of the All Party Parliamentary Group against Antisemitism, have written to Mr Corbyn to urge him to take action to tackle "this poison in our ranks".
Posting a copy of the letter on Twitter, Mr Streeting said: "@jeremycorbyn's statement on Monday has not been heeded by all those claiming to support him. @JohnMannMP and I have written about the abuse that's taken place in the last 48 hours and the action that's needed."
The letter warns that there must be a "turning point for our Party on antisemitism", and says Mr Corbyn should meet with Jewish colleagues and "send a message of solidarity" to all Jewish members demanding that social media abuse against them ends.
It adds: "Without action, this issue will not go away. We ask you to lead our response in the robust terms of your most recent statement."
Earlier shadow business secretary Rebecca Long-Bailey said the party would be rolling out a "political education programme" to ensure party members were fully aware of the issue.
"I think there is a lot more that needs to be done and I think Jeremy addressed that clearly yesterday. He has always been a militant opponent of anti-Semitism," she told the BBC Radio 4 Today programme.
"But too often, I think, the issue has been dismissed as a few bad apples when we needed to take very serious root-and-branch action to root out the cause of the problem.
"There will be clear efforts now to roll out a political education programme specifically to make sure that every single person in the Labour Party is aware of all forms of anti-Semitism."