In August the Sunday Times reported some Labour MPs had considered the party as a possible escape route if, as expected, Corbyn triumphs in his leadership contest with Owen Smith.
And last week, the Greenwich branch of Momentum issued a rallying call to members, asking for volunteers to stand at a local annual general meeting in November.
In an email sent to members on 12 September, the Greenwich group wrote: “There are now some signs that the [Parliamentary Labour Party] and their local associates are now actively engaging with the Greenwich branch of the Co-op party which meets every six weeks.”
“We need to turn out in force at the Co-op Party Greenwich AGM....to ensure that it is not used by the right to further their aims.
“If anyone wishes to stand as a Co-op delegate to their relevant constituency party, please let us know as soon as possible.”
The Greenwich group made the call just two days after the Co-op party's chair warned it wouldn't tolerate entryism.
Speaking at the party's conference on 10 September, chair Gareth Thomas said: “The Co-operative party has a strong interest in seeing the Labour party come through its current travails, because they are our electoral partner and many of us are members of both parties.
He added: “We say to our brothers and sisters in the Labour family – if you share our co-operative values and principles please join us in our task of creating a more co-operative Britain. If you want to use our Party for other ends then you should think again because the Co-operative party national executive committee have been clear that we will not tolerate entryism of any form. From any group.”
An agreement between the two parties means it is possible to be a member of both groups, and a total of 26 MPs currently sit in parliament on a joint Co-op/Labour ticket.
They take in a broad range of the party's political views, including both John Woodcock, who was named on a recent “hit list” of rebels, and current shadow international development secretary and Corbyn loyalist Kate Osamor.
Co-op party rules mean that new joiners are unable to stand for election until at least three months after joining - meaning members of the campaign would have had to become part of the Co-op in August to be elected at the local AGM in November. However, recent recruits are still allowed to vote.
A Momentum spokesman said: “Labour members across the country were concerned by press reports that the Co-op might be used as a vehicle by those who oppose Jeremy Corbyn and his ideas to sabotage our efforts to take on the Tories.
“Momentum members are part of organisations right across the Labour movement, including the Co-op and are free to take part in their democratic processes.”