This article explores the links between the assertion of British imperial identities and the anti-Catholic discourse and practices of a network of evangelical societies which existed and flourished in Britain and in the dominions from the halcyon days of the empire to the late 1920s. These bodies shared a broad evangelical definition of Protestantism and defended the notion that religious beliefs and their political implications formed the basis of a common British heritage and identity. Those who identified themselves as Britons in Britain and in the dominions brought forward arguments combining a mixture of pessimistic interpretations of British history since the passing of the Catholic Emancipation Act with anxieties about ongoing Irish Catholic immigration and an alleged global papist plot. They were convinced that Protestantism was key to all civil liberties enjoyed by Britons. Inspired by John Wolffe's pioneering work, the article examines constitutional, theologico-political and socio-national anti-Catholicism across Britain and its dominions.