Senior communal and Labour figures have warned that the election this week of three hard-left activists to the party’s governing National Executive Committee (NEC) will have deeply damaging repercussions for the party’s handling of antisemitism investigations.

Jennifer Gerber, director of Labour Friends of Israel, forecast that their election could “stifle” efforts to combat antisemitism within the party, while another key Jewish figure in Westminster said it was now likely that “all is lost”.

The first act of the new hard-left-dominated NEC on Tuesday was to remove the existing chair of the party’s disputes panel — which investigates antisemitism cases, sexual harassment allegations and disciplinary breaches — and replace her with a Momentum office holder. One leading communal source said it was now a “likely scenario” that antisemites and extremists will be “given a free pass”.

The source continued: “If that happens, we will all come out swinging, and hard”.

On Monday, Jon Lansman, the founder of the Jeremy Corbyn-supporting Momentum organisation, was elected to the NEC along with two other Momentum-backed activists, Yasmine Dar and Rachel Garnham.

The following day, the NEC voted by 22 to 15 to remove Ann Black, the widely respected chair of the party’s disputes panel, and replace her with veteran hard-left activist Christine Shawcroft.

Ms Black was described by one communal source as “someone who demonstrated an understanding of antisemitism on the left, and was acceptable to all wings of the Labour movement. It shows how far the Labour Party has shifted in the past two years”.

In May 2016, Ms Shawcroft accompanied Tony Greenstein, the Jewish anti-Zionist activist, when he was questioned as part of Labour’s investigation into his suspension for an alleged breach of party rules. She acted as his silent witness.

In 2015, Ms Shawcroft was herself suspended from the party for supporting Lutfur Rahman, the disgraced former mayor of Tower Hamlets, the London borough in which she previously led the local Labour group.

Mr Greenstein’s full disciplinary case — and those of a number of other hard-left activists under investigation — is due to be heard by Labour’s national constitution committee next week.

It is understood those hearings will take place as planned as the NCC is a different committee to the NEC’s disputes panel and is said to be unaffected by this week’s changes.

But the Jewish Labour Movement (JLM) warned Mr Corbyn there could be “no further excuses for failure to deliver a gold standard in acting on antisemitism”.

Jeremy Newmark, JLM chair, said the group would judge the disputes committee “by real results and actual outputs, not by leaks and speculation”.

He said the JLM had informed Mr Corbyn’s office that serious disputes were “currently taking far too long to conclude”.

Mr Newmark added: “The next few weeks will see the NCC consider a number of high-profile cases of antisemitism. The results will send an important signal to the Jewish community.”

Ms Gerber said: “The hard-left have spent two years denying Labour has a problem with antisemitism. They must not now be allowed to stifle investigations into it, or action to combat it.”

Tuesday’s NEC meeting saw a number of cases of alleged Jew-hate dismissed, although some were passed to the NCC for consideration. It also reportedly included a discussion of whether the word “yid” was antisemitic.