The adoption of the ‘Popular Front’ tactic by the Communist International at its Seventh Congress in July 1935 reflected Soviet concern at Germany's growing power and indicated a desire to work with non-communist parties against the rise of fascism. In France and Spain, the 1935 decision led to the establishment of Popular Front governments based on alliances between Communist, Socialist and Radical ov Liberal Parties. In Britain, Communists had initially placed a primary emphasis on the achievement of a united front of ‘working-class’ parties only – the aim of the abortive Unity Campaign. The collapse of this campaign enabled the CPGB to concentrate on a broad Popular Front calling for a grand alliance of Socialist, Liberal and dissident Tory opponents of the National Government.

Yet while it was the Communists who gave the tactic its name (and who helped to give it a bad reputation), the idea was not pioneered on the far left, nor was support for it restricted to Communist sympathisers. Indeed a progressive alliance of some kind was a frequent subject for discussion in the 1930s, and at one time or another leaders of every party or faction who wanted to change Government policy considered it seriously.

The idea developed gradually – with roots on the right as well as the left.