The pro-CPGB faction in the ILP (the Revolutionary Policy Committee) of the 1930s, which contained people like Jack Gaster, Hetty Bower and numerous others is well known and documented. If you can cope with dusty archives, you can find a run of its bulletins in Manchester. Communist scholars are not debarred from using those materials if they are willing to put the work in.

At a public event on CPGB history held at St John Street in the party's dying days, I recall George Matthews reminiscing about his early career in the Labour Party, even getting selected as Labour PPC for some unwinnable seat in 1938 while secretly holding a CPGB card. He and several others had had to leave Labour after September 1939, when defending the CP's new line on WW2 made their position untenable within Labour. Peter Fryer, who was in the audience, made a wisecrack about this being 'not entrism, but departurism'...