Orwell based his list on a strictly private notebook he had maintained since the mid-1940s of possible "cryptos", "F.T." (his abbreviation for fellow travellers), outright members of the Communist Party of Great Britain, agents and sentimental sympathisers.
One of Orwell's biographers, Bernard Crick, thought there were 86 names in the list and that some of the names were written in the hand of Koestler, who also co-operated with the IRD in producing anti-Communist propaganda [REF].