The leader of the ‘Momentum’ party-within-a-party group which supports Jeremy Corbyn as Labour leader has acknowledged the “major problem” of anti-Semitism in Labour, citing the sudden surge in party membership under Mr Corbyn as a factor in the emergence of the scandal.

Jon Lansman, the leader of Momentum which critics claim acts as an enforcer for Mr Corbyn’s leadership — and which recently launched an effort to kick out of Parliament rebel MPs who left Labour over anti-Semitism and Brexit concerns — told BBC radio he was “extremely upset” by the defections.

Introduced on BBC Radio 4’s Today programme as the “third most influential person within Labour,” Mr Lansman, who is Jewish, blamed the sudden influx of new Labour members since Mr Corbyn became leader for the emergence of anti-Semitism as a force within the party.

He said: “I think that one aspect of the problem is that the party trebled in size, we took in over 300,000 new members. Amongst those, are members who are attracted to conspiracy theories, and unfortunately online Facebook groups can become an arena for which a minority with hardcore anti-Semitic views can infect [other members].

“There are conspiracy theorists in many parts of the political spectrum, I don’t think it’s exclusive to the Labour Party, but the Tory Party is a smaller party and an elderly party, and the role of social media in fomenting and spreading some of the poison is, therefore, more of a problem in the Labour Party.”

Mr Lansman’s Momentum group, which he founded in 2015 when Mr Corbyn became the leader, has been at least in part a driving force behind that rise in membership to the party. The group requires all Momentum supporters to also join the Labour Party. Lansman is also a member of Labour’s ruling body.

Saying that Jeremy Corbyn has been an anti-racism campaigner his whole life, Lansman told the radio host that Mr Corbyn taking personal responsibility for investigation into anti-Semitism could be inappropriate, but that internal party investigations were ongoing.

Despite the evident problems Labour is experiencing, as it has over the past few years apparently lurched from one anti-Semitism scandal to the next, Mr Lansman insisted the party was not institutionally anti-Semitic, but nevertheless has a “major problem”.

“It always seems to me we underestimate the scale of it. It is a widespread problem — it’s now obvious that we have a much larger number of people with hardcore anti-Semitic opinions which unfortunately is polluting the atmosphere in a lot of constituency parties and in particular online.

“We have to deal with these people, and I think it is a responsibility of everyone in the Labour Party, from the top to the bottom, to report cases,” he said.

The Labour Party was rocked last week by the formation of the Independent Group — seven of their Members of Parliament who walked away, citing concerns over the party’s handling of both the Brexit debate and internal anti-Semitism problems.

By the end of the week, nine Labour MPs and three Conservatives had left their parties to either join the Independent Group or to become actual independent, unaffiliated MPs.

Some took the opportunity to make personal attacks against Mr Corbyn. When he walked out of the party on Friday, former Labour MP Ian Austin told a local newspaper of his decision: “I think Jeremy Corbyn and the people around him have turned what was a mainstream political party into something very different.

“I think they’ve created a culture of extremism, intolerance and bullying. And I think that’s unbelievable, that decent people who have devoted their entire lives to mainstream politics are being driven out by this culture of extremism and in some cases, anti-Semitism… I have to be honest and the truth is that I have become ashamed of the Labour Party under Jeremy Corbyn.

“I always tell them the truth and I could never ask local people to make Jeremy Corbyn Prime Minister… I am appalled at the offence and distress Jeremy Corbyn and the Labour Party have caused to Jewish people… The hard truth is that the party is tougher on the people complaining about anti-Semitism than it is on the anti-Semites.”

Oliver JJ Lane is the editor of Breitbart London — Follow him on Twitter and Facebook