ANTI-Semitism is more widespread within the Labour Party than was thought, and complaints cannot be dismissed as right-wing smears, the leadership of the Jeremy Corbyn-backing Momemtum movement has said.

Momentum’s National Coordinating Group (NCG) released a statement acknowledging the anger of Britain’s Jewish community at the “numerous” cases of anti-Semitism within the party and its failure to deal with them “in a sufficiently decisive, swift and transparent manner”.

The group announced Momentum was bringing in outside organisations to run awareness training on the issue. The move came as a Jewish member of Labour’s ruling National Executive Committee (NEC), Rhea Wolfson, said she was frustrated at the pace of action on anti-Semitism.

Leader Corbyn is facing demands to speed up investigations into a backlog of around 70 complaints of anti-Semitism, including one against Ken Livingstone. Labour has moved to distance itself from a series of pro-Corbyn social media groups after a Sunday newspaper investigation found they contained hundreds of violent and abusive messages.

Former speaker of the House of Commons Lord Martin called for an extraordinary conference of party members, saying: “If you ran a restaurant, and it was dirty and there were cockroaches, you wouldn’t get away with saying ‘the restaurant down the road is dirty and has cockroaches too’.”

Momentum’s NCG includes Christine Shawcroft, who quit Labour’s disputes panel and the NEC amid criticism of her opposition to the suspension of a council candidate accused of Holocaust denial.

The statement said: “Accusations of anti-semitism should not and cannot be dismissed simply as right-wing smears nor as the result of conspiracies. Current examples of anti-Semitism within the Labour Party are not only a problem of a few, extreme ‘bad apples’ but also of unconscious bias which manifests itself in varied, nuanced and subtle ways and is more widespread in the Labour Party than many of us had understood even a few months ago.”

While Corbyn’s opponents were “opportunistically using this issue as a way to undermine his leadership”, this did not reduce the need to challenge anti-Semitism, the statement said. Momentum will review its constitution and complaints procedures to ensure they fulfil a commitment to “stamping out” anti-Semitism.