Editor’s Note: I would go far further than Stephen does here. Membership with a far-left organisation like Momentum, whose ambition is to take over the Labour Party and re-fashion it as a far-left vehicle, is not compatible with membership of the Labour Party. Momentum should be proscribed.

Momentum, Jeremy Corbyn’s praetorian guard, it’s argued by centrist Labour politicians, is the new front organisation for far-left parties like the Socialist Party, Workers Liberty and Left Unity. It represents a major threat to the survival of Labour.

Moderates fear that Momentum will be used as a vehicle to de-select MPs and councillors when new boundaries are set in 2018. Although hard-left groups are already in Labour’s ranks, this isn’t the first time that the far-left has tried to infiltrate the Party with its own revolutionary agenda.

Back in the eighties, the main ‘entryist’ organisations were the Trotskyite Militant Tendency and the Lennist Socialist Organiser. Militant, with over 8,000 active members, had its powerbase in Liverpool, Brighton, East London and Newcastle. A highly disciplined, well-structured set-up with a cult-like mentality, Militant’s central aim was to take over and transform the Labour Party into a revolutionary force to overthrow capitalism. The fact that Labour’s Constitution in 1918 rejected the revolutionary road to socialism with ‘democratic centralism’ at its core cut little ice with Militant’s leadership.

After a decade of in-fighting, the Party under Neil Kinnock managed to expunge both ‘sects’ from its ranks by 1991.

Today Militant, under its re-branded name, the Socialist Party, is back along with Workers Liberty and the sinister sect Left Unity. Left Unity set up by film director Ken Loach in 2013 is committed to a radical socialist and feminist programme. In the 2015 it stood against Labour in several seats but polled badly.

Momentum, set up in summer 2015, has 30,000 members. 1,000 are believed to be members of other far-left parties. The movement has its own organisational structure, four paid workers, headed up by former ‘Bennite’ Jon Lansman and operates out of Corbyn’s London Parliamentary GHQ. Throughout the North Momentum has established branches on Tyneside, Sunderland, Hexham, Middlesbrough, Leeds, and Merseyside.

For 172 Labour MPs Momentum is no more than a front for a coalition of far-left parties whose real motive is to facilitate the de-selection of those who disagree with them. Key targets include Hilary Benn, Stella Creasy, Chukka Ummana and Frank Field. Labour’s deputy leader, Tom Watson, has described the faction as “a rabble”, and warns of “entryism”. The Birkenhead Labour MP Frank Field believes it to be “a party within a party”, with a sinister agenda which goes beyond protecting council jobs and services.

Is this an internal Labour Party “moral panic”, as some have suggested? Or has Labour been infiltrated by “modernised”, latte-drinking Trots? It’s true that  out in the cold Militant did rebrand itself under the leadership of Peter Taffe and his daughter Nancy. It has with some success joined Momentum. Yet author Andy Beckett argues, though a hard-left movement, Momentum is not a front for a modernised Militant Tendency. Labour’s current leader did defend Militant in the eighties as part of “a witch hunt against the left’’, but Corbyn was never a member of the outlawed sect.

Nor is it the case that Corbyn’s “new politics” is attributable to “far-left entryism”: rather, as Beckett points out, it stems from the peculiar phenomena of “Corbynmania” which captured the imagination of idealistic young people alienated from mainstream politics and civil society. Yet as the last fortnight has shown Momentum has an agenda far more disturbing than shaping Labour Party policy.

For those of us committed to social democracy and mutual respect Momentum as a movement must be scrutinised. Labour must learn the bitter lessons of the past if it is to continue as a major player on the geo-political landscape.