Labour deputy leader Tom Watson has written to Jeremy Corbyn after the leader's team accused him of "peddling baseless conspiracy theories" about the hard left seeking to infiltrate the party.
In the latest signal of the pair's strained relationship, Watson used an open letter to ask Corbyn to confirm whether he believed members of the Socialist party and the Alliance for Workers' Liberty should still be banned from Labour.
These two groups – formerly known as Militant and Socialist Organiser respectively – were proscribed during Neil Kinnock's leadership of the party.
In an interview with The Guardian on Tuesday, Watson said Labour was at risk of being taken over by hard-left "Trotsky entryists" who were "twisting the arms" of young party members.
Hours later Corbyn's leadership campaign team released a statement saying: "Rather than patronising members and peddling baseless conspiracy theories about 'Trotsky entryists', he should be working with Jeremy to unite our party so that we can get back to campaigning to dislodge this Tory government, and help elect a Labour government in its place."
In the letter to Corbyn on Wednesday, Watson told the leader he assumed the statement "was not authorised by you".
But he added: "I think it important I set out my position. As far as I understand it, we are in agreement when it comes to dealing with members of other political parties and membership organisations that attempt to use the party as a vehicle to achieve their revolutionary aims."
Watson said that while many members of pro-Corbyn pressure group Momentum were "genuine in their desire to campaign vigorously against Tory inequality", there was "no denying that tightly organised factions are also organising within Momentum and the party".
He insisted it was "not a conspiracy theory" to say that members of the Socialist Party and the Alliance for Workers' Liberty were joining Labour, saying: "It's a fact."
And he summarised the tactics he said were being used by "Momentum members with links to far left parties" on how to take control of Labour party meetings:
– Making the meetings boring. "Flood the branches and constituency meetings with procedural requests, the minutes of the last meeting and process. This turns off the faint-hearted."
– Making the events adversarial. "Uncomradely questions to sitting councillors and the MP, challenging the chair's method and motive ... This behaviour basically reduces the attendance of the remaining sensible types."
– Once the "troublesome moderates" are out of the way, "motions and debates on policy and political positions will commence – each will pass almost by acclaim".
Watson concluded: "I hope this note helps to dispel any remaining notion that entryism is a 'conspiracy theory'. With vigilance and leadership, I know we can tackle it together."
A Momentum spokesperson distanced the organisation from the tactics apparently being used in Labour meetings, which were first outlined in the book Militant by Michael Crick.
"The description quoted from Michael Crick’s book runs entirely contrary to Momentum’s ethos and ways of organising," they said.
"Momentum wishes to help the Labour party become more open and participatory. Our movement helps bring people into politics and the labour movement, not shut them out. Momentum members and supporters would have no truck with the types of organising described by Crick."