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Jeremy Corbyn's Left-wing campaign group Momentum has shut its youth wing for reportedly bringing the organisation into “disrepute”.

Momentum chair Jon Lansman ordered the Momentum Youth and Students (MYS) organisation, which has 5,000 online followers, to hand over passwords to social media accounts in a letter sent to it last night.

It was not clear which posts had offended Mr Lansman, but former committee members of the organisation for under-30s claimed in a blog post that in the past the group had been “hostile” and put “sectarian vendettas” above co-operation and campaigning.

They also hit out at “bad-spirited jokes” being put online, which may refer to a number of Facebook posts about deselections of Labour MPs littered with emojis and posts celebrating the Russian revolution.

In his letter leaked online last night, veteran Left-winger Mr Lansman wrote: “The MYS social media accounts have at times been used in ways which have brought Momentum into disrepute and which are inconsistent with Momentum’s code of ethics, which seek to promote values consistent with those of Jeremy Corbyn’s two leadership campaigns ‘of fair, honest debate focused on policies, not personal attacks or harassment’.’’

Momentum is widely credited with helping Labour far outstrip expectations during the general election by rallying younger members and spreading campaign messages through viral social media videos. It also ran a nationwide carpool taking activists to marginal seats to campaign.

However since Momentum was founded in 2015 it has been repeatedly embroiled in rows with moderate members of the Labour Party who feared it was orchestrating the deselections of MPs.

In London it has been accused of organising the Left-wing takeover of the centrist-run Labour Haringey council after local elections in May.

It is also being investigated by the Electoral Commission over its general election expenditure.

The youth wing, founded in 2016, had 200 people at its first meeting. But thousands now follow its national Facebook group and regional pages, and it also runs its own “political schools” for young activists.

However, Mr Lansman has said MYS has never been affiliated to the main organisation, it does not recognise their work and it has not given it permission to use its logos or branding.

Mr Lansman wrote: “I respectfully ask those involved to cease to use Momentum’s name and to close down the social media accounts or hand them over to a member of the national office team.”

It is understood Momentum is working on developing a new youth wing later this year.

As Mr Lansman is attempting to win a seat on Labour’s National Executive Committee, critics have suggested his timing in shutting down the youth wing comes after the majority of young members will have already cast their ballot. Voting closes on Friday.