Amount of testimony in front of EHRC will make it hard to support Corbyn’s claim that problem is down to ‘small number’

At least 100 witness testimonies describing alleged antisemitic behaviour will be submitted to the equality watchdog’s official investigation into the Labour party.

The number will dismay many in the party and make it difficult to support Jeremy Corbyn’s earlier claims that its problem with antisemitism was down to a “small number of members and supporters”.

The Equality and Human Rights Commission’s decision last week to investigate whether “the party unlawfully discriminated against, harassed or victimised people because they are Jewish” came as Labour’s antisemitism problem showed no sign of abating.

Last week the party was forced to suspend Labour NEC member Peter Willsman for suggesting that the antisemitism row was “almost certainly” the work of the Israeli embassy.

Some senior Labour members said that if it was true that Willsman had made such a claim, he should be expelled.

They contrasted the decision only to suspend him with the near immediate expulsion of the former spin doctor Alastair Campbell for admitting that he voted Lib Dem in the recent European elections.

Peter Mason, national secretary of the Jewish Labour Movement, confirmed to the Observer that it had already submitted scores of testimonies to the watchdog.

Mason said that a further call for evidence was being made to JLM members, and that when the second round of submissions was presented to the EHRC, the total number of confidential witness statements would be more than 100 and run to more than 1,000 pieces of paper.

The JLM’s previous call for evidence from members was conducted discreetly – there was no public appeal. “At some point in the not too distant future there will be a second document,” Mason said – and the next request could see many more members come forward.

The Jewish Labour Movement is likely to play a key role in the commission’s investigation. “They don’t have to consult us but, given the material we have supplied to them and anything we might continue to give them, it’s highly unlikely that we won’t be consulted,” Mason said.

The Campaign Against Antisemitism and Labour Against Antisemitism are expected to make submissions as well, suggesting that the EHRC investigation will take considerable time.

Mason said that antisemitism within the party had shown no signs of reducing since the investigation was launched: “It’s ongoing. The Labour party has just emerged from the pre-election period and, for that period, constituency Labour parties aren’t allowed to hold meetings, but now that they can again, we’ve got constituencies debating and rejecting the EHRC, calling it all a smear, diminishing the experience of Jewish members.

“Nothing has changed. We continue to see the same behaviour that we have seen for a very long time and no action taken to tackle it.”

The timing of the investigation could be significant. Publication of the EHRC’s findings – and its potential recommendations to the party – might damage Labour’s standing with voters at a time when it is losing ground to the Brexit party and the Liberal Democrats.

But it is believed that the watchdog is unlikely to finish the inquiry before the end of the year. “When they go in and kick the tyres, they might realise there’s a lot there,” Mason said.

The commission could demand that internal Labour party emails, documents and text messages be handed over. Any attempt to destroy relevant information would be considered a criminal act.

The EHRC confirmed: “We have the power to compel the Labour party to disclose relevant information to us.”

Labour has insisted that it “is fully committed to the support, defence and celebration of the Jewish community and is implacably opposed to antisemitism in any form”.

Gideon Falter, chief executive of Campaign Against Antisemitism, which made the initial complaint to the EHRC, said: “We are pleased that the commission’s terms of reference closely follow our recommendations and will see a root and branch investigation of the Labour party’s antisemitic discrimination, victimisation and harassment, as well as how the party’s processes and decisions contributed. We commend the commission for acting on our referral and we have full confidence in its resolve to investigate thoroughly and deliver justice.”