Contrary to myth, the most numerous and strategically significant group to support the Popular Front campaign in Britain was not the Communist Party but the left of the Labour Party. The success or failure of the proposal to join the ‘parties of progress’ in a common struggle against the Conservative government depended solely on whether the Labour left could persuade the rest of their party to agree to it. This book is therefore mainly about the Labour left. It aims to show that the left's support for the Popular Front campaign, and to a lesser extent the United Front campaign before it, can best be explained in terms of the left's place in the mainstream of the British progressive tradition. This view implies that the campaigns themselves are best seen as episodes in that tradition, and demands reinterpretation not only of the history of the Labour left in the 1930s, but also of the nature of the United Front and Popular Front campaigns, and of the British progressive tradition itself. The book is devoted equally to each of these three interlocking tasks.

The historiographical and conceptual problems that surround this subject-matter are considerable and require some preliminary discussion. To begin, however, it will be helpful to provide a brief sketch of the United Front and Popular Front campaigns.

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The United and Popular Front campaigns are fairly straightforward episodes, at least in outline.