Jeremy Corbyn’s allies have been accused of using a report to “smear whistleblowers” in a bid to “discredit allegations” of anti-Semitism in the Labour Party during his tenure.

The former Labour leader, replaced by Sir Keir Starmer 10 days ago, saw his four-and-a-half years in charge dogged by complaints of racism against Jews and accusations senior officials were slow to crack down on members who promoted anti-Semitism.

But an extensive internal investigation carried out in the final month of Mr Corbyn’s reign has concluded that “factional opposition” in the upper echelons of the party towards the Islington North MP contributed to “a litany of mistakes” that hindered the effective handling of the issue.

In the dying days of Jeremy Corbyn's leadership, Labour appears to have invested in a desperate last-ditch attempt to deflect and discredit allegations of anti-Semitism

The report, seen by PA news agency, claimed to have found “no evidence” of anti-Semitism complaints being handled differently to other forms of complaint, or of current or former staff being “motivated by anti-Semitic intent”.

It states that in 2019, half of all anti-Semitism complaints came from a “one individual” who the reports accuses of being “rude and abusive” to party staff.

The dossier was compiled after its authors trawled through 10,000 emails, along with thousands of private WhatsApp communications between former senior party officials, with whistleblowers who gave evidence to last year’s BBC Panorama investigation on anti-Semitism within Labour singled out for criticism.

Those include the former general secretary Lord McNicol and Sam Matthews, the former acting head of the governance and legal unit.

PA understands the 860-page document was intended as a internal report and was not planned to be submitted to the Equality and Human Rights Commission (EHRC) for consideration during its probe into Labour’s handling of the crisis.

It was put together to enhance the party’s understanding of how disciplinary processes have operated over a number of years, sources said.

But the Campaign Against Anti-Semitism, the group that filed the complaint about Labour to the EHRC, has demanded the file be handed over for consideration as part of the inquiry.

Gideon Falter, chief executive of the campaign, said: “In the dying days of Jeremy Corbyn’s leadership, the Labour Party appears to have invested in a desperate last-ditch attempt to deflect and discredit allegations of antisemitism.

“Rather than properly dealing with cases of anti-Semitism and the culture of anti-Jewish racism that prevailed during Mr Corbyn’s tenure, the party has instead busied itself trawling through 10,000 of its own officials’ e-mails and WhatsApp messages in an attempt to imagine a vast anti-Corbyn conspiracy and to continue its effort to smear whistleblowers.

“It is a disgrace that the 450,000-word report, which itself claims to ‘prove the scale’ of anti-Semitism in the party and serves as an exhibit of the party’s failure to address the crisis, is being kept secret.”

A Labour spokeswoman said: “The party has submitted extensive information to the EHRC and responded to questions and requests for further information, none of which included this document.”

Jewish leaders last week praised Sir Keir for having “achieved in four days more than his predecessor in four years”, with his steps to tackle anti-Semitism in the party.

He spoke with community leaders via web conference to re-iterate his apology over Labour’s failure to deal with the scourge and confirmed he had asked for reports on all outstanding cases to be handed directly to him.