Recent historical treatment of Anglo-Irish relations in the 1930s has overlooked the complex nature of the legal disagreements between the two countries during that period. This article provides an account of some of the fundamental points of legal disagreement between the countries. It explains how differences of opinion as to the structure of intra-commonwealth constitutional relations led to conflict between the British government and that of the Irish Free State, with particular reference to the oath of allegiance crisis. It considers how other commonwealth countries saw these points of conflict. It concludes with a re-appraisal of the roles of Lord Hailsham and de Valera in Anglo-Irish relations, as examples of differing attitudes towards the commonwealth relationship.