The predominant style of church design for Roman Catholic churches in Britain from around 1920 until 1960 was a simplified Romanesque or Byzantine revival based loosely on north Italian models. Many of the architects who favoured this style remain little-known, as regional architects specialising in a mode of architecture deliberately opposed to the development of modernism. F. X. Velarde in Liverpool; Reynolds & Scott in Manchester and E. Bower Norris in the Midlands; H. S. Goodhart-Rendel and Adrian Gilbert Scott, and many others, favoured variants on the style. Few needed to explain their motivations, since they were always in demand by the clergy, who were aware that the Church explicitly required ‘traditional’ forms. Those who attempted an explanation articulated a defence of a Catholic tradition of church-building. It was a tradition, however, that only began in the early twentieth century with the completion of J. F. Bentley’s Roman Catholic Cathedral at Westminster, and was actualised by architects who derived their designs from this model, from books on Italian Romanesque and Byzantine architecture, from their travels and from each other. At the same time many architects proposed that their tradition was also modern, often embracing new materials and techniques and incorporating aspects of modern styles. In some extraordinary cases, church buildings in a fully-understood modernist style accommodated historicising elements to express a development of this supposed Catholic tradition. This paper will consider the ways in which such church architecture could be conceived of as simultaneously adhering to ‘tradition’ and to the ‘modern’. Bringing both terms into tension, neo-Romanesque and Byzantine church architecture of this period can be considered less as the retrograde rejection of modernism by an ‘other’ branch of architectural practice than as highly symptomatic of twentieth-century anxieties and contexts.