A senior Labour MP facing the threat of deselection has told Sky News she has sent a dossier on "entryism" by far-left activists to Jeremy Corbyn and party bosses.
Louise Ellman, veteran MP for Liverpool Riverside, claims members of the Momentum group are operating as a "party within a party" in her constituency and is demanding an inquiry.
She told Sky News she has sent her evidence to Mr Corbyn and Labour's ruling body, the NEC, and insists she will fight any attempts by her left-wing opponents to deselect her.
The dossier says: "While Liverpool Riverside has always had a large and active Constituency Labour Party it has experienced an explosion in membership following the general election in 2015, with many members who voted, campaigned or stood for rival parties, mainly the Trade Union and Socialist Coalition and the Green Party.
"Indeed many of the most vocal and active members of Momentum have continued to support the efforts of rival parties even after Jeremy Corbyn's victory in the Labour leadership election in September 2015."
It adds: "It's not difficult to spot the obvious parallels in the respective conduct and practices of Liverpool Riverside Momentum and Militant in the 1980s."
The dossier describes a "high level of hostility" towards Louise Ellman, 70, who is Jewish, largely because of her support for the state of Israel.
And it reveals that Riverside Momentum meets several times a month and holds caucuses in advance of Constituency Labour Party meetings.
On its members, the dossier says: "The vast majority of the key figures of the organisation within Liverpool Riverside Momentum group have been hard left activists who have operated in political parties and organisations hostile to the Labour Party."
It concludes: "The Riverside Momentum group are actively planning to take control of the Liverpool Riverside CLP executive committee with the hopes of using such power to bring about the deselection of its sitting Labour MP and Labour councillors.
"It is no stretch to label the activities, plans and structures of the Momentum group in Liverpool as those of a party within a party."
But the MP's allegations are rejected by Mr Corbyn and his allies, who have told Sky News that Momentum members are mainly "young people who want to join the Labour Party and get involved".