A major reason for the NEC's hesitations on the Popular Front was that the Communist Party had been agitating vigorously for one since 1936. The Communists did not make a fundamental distinction of principle between the united front and the popular front – the first was seen as a preparation for the second. The Labour Party Executive was therefore inclined to regard both with equal suspicion as tactics designed principally to increase Communist influence in the Labour Party. This suspicion was not diminished by the linking of united and popular fronts with the situation in Spain.

Closely associated with the Communist Party, and providing a prolific propaganda backing for Communist campaigns for aid to Spain and for united and popular fronts, was the Left Book Club. ‘The Club devoted all its efforts to the explanation and advocacy of a People's Front’, recalls its leading official. The Club certainly printed more on the subject than anybody else, was responsible for getting the idea widely discussed in political circles in Britain – and created a firm association in the minds of most people between the Popular Front and Communism.

The Club was the brainchild of Victor Gollancz, pacifist schoolmaster turned successful publisher. The basic scheme of the Club was simple. For 2s 6d members received a ‘Left Book of the Month’, chosen by the Selection Committee – which consisted of Gollancz, John Strachey and Harold Laski. Left-wing books could be guaranteed a high circulation without risk to the publisher, while members received them at a greatly reduced rate.