From a letter sent in 1949 by George Orwell to Celia Kirwan of the British Secret Service's Information Research Department. In a meeting a few weeks before sending the letter, Orwell gave Kirwan the names of various writers he regarded as potential communist collaborators; the Secret Service subsequently opened files on all of those named. Orwell's letter was released by the British Public Records Office in July; the names he originally provided have not yet been made public.
I couldn't think of any more names to add to the list of writers except Franz Borkenau (the Observer would know his address) and Gleb Struve (he's in Pasadena, California, at present), the Russian translator and critic. Of course, there are hordes of Americans, whose names can be found in the (New York) New Leader, the monthly Jewish paper Commentary, and the Partisan Review.
I could also, if it is of value, give you a list of journalists and writers who are in my opinion crypto-communists, fellow travelers, or inclined that way and should not be trusted. But for that I shall have send you a notebook which I have at home. If I do give you such a list it is strictly confidential, as I imagine it may be libelous to describe somebody as a fellow traveler.