This thesis investigates the leftist intellectuals in Britain who opposed the Air Raid Precautions (ARP) plans of the central government in the 1930s. It examines how a coalition of the far left advocated an alternative shelter plan and the political ideas on which this program was based. In contrast to the government policy of individual household shelters, these critics believed that the central government was obligated to provide public underground shelters for all citizens. Critics of government ARP included the Communist Party, radical scientists and architects, far left and Labour local councils, and members of the Parliamentary Labour Party. Their advocacy of bomb-proof shelter plans, funded by the central treasury, pitted an activist social mentality against the liberal ethic of volunteerism espoused by the government. Drawing on a home-grown radical tradition, these critics invoked the idea of a "People's War." Through the observation of deep shelter construction in the Spanish Civil War, they promoted a model of radical volunteerism in which citizens were active participants in their own civil defence. This study's primary aim is to offer a new understanding of the politics of the British left in the interwar years viewed in light of this specific issue. It demonstrates how the British left understood the relationship between the state and its citizens, and argues that leftists used civil defence to articulate their ideal of a politically active and engaged citizenry. This thesis contributes to understanding of the British left in the 1930s, demonstrating how critics used ARP to emphasize leftist nationalism and citizenship ideals and how moderate, cooperative policies evolved in preparation for war. / Thesis / Doctor of Philosophy (PhD)