The Labour deputy leader Tom Watson has warned that his party could be taken over by old Trots - Trotskyist entryists, who have no interest in winning elections but instead see Labour as a vehicle for revolutionary socialism.
But what is a Trot, who was Leon Trotsky and what do his followers in Britain actually want?
David Aaronovitch is joined by:
Prof John Callaghan, Salford University
Amy Leather of the Socialist Workers Party
Michael Crick author of 'The March of Militant' and a journalist with Channel 4 News
Dr Bert Patenaude, Stanford University, author of 'Trotsky: Downfall of a Revolutionary'
Producer: Joe Kent
Researcher: Kirsteen Knight
Editor: Innes Bowen.
