The timing of secularization in Britain remains a contested topic among historians and sociologists, some regarding it largely as a post-Second World War phenomenon (with the 1960s a critical decade), others viewing it as a more gradual process commencing in the Victorian era. The inter-war years (1918–1939) have been little studied in this context, notwithstanding a coincidence of social, economic, and political circumstances which might have been expected to trigger religious change. The extent of religious belonging during this period is reviewed, with reference to quantitative evidence, from two perspectives: churchgoing, and church membership and affiliation. Trends in church attendance are documented, including the demographic variables which shaped it and the effect of innovations such as Sunday cinema and Sunday radio broadcasts of religious services. A conjectural religious profile of the adult population of Britain, c. 1939 reveals that, while, relative to population, there was only marginal growth in professed irreligion and non-Christian faiths since c. 1914, there was accelerated decline in religious worship (notably in terms of regularity) and active affiliation to Protestant denominations. This shift to nominalism particularly impacted the historic Free Churches (the phenomenon had long existed in the Church of England). Examination of these two religious indicators for the inter-war years thus lends further support to the view that secularization in Britain is best seen as a progressive and protracted process.