The British Labour Party became increasingly aware after the First World War that it was potentially an alternative government in waiting. In opposition the party was generally supportive of Irish nationalism. It supported Home Rule and was adamantly opposed to the partition of Ireland contained in the 1920 Government of Ireland Bill. As the demands of Irish republicans became more radical and their tactics more extreme the Labour parliamentary leadership became wary of the electoral damage that could ensue if it was perceived by the British public that it was sympathetic to revolutionary Irish republicanism. Despite the fact that the Anglo-Irish Treaty of 1921 was inconsistent with Labour party Irish policy cementing as it did the partition of Ireland as well as hardly being an exercise in “self-determination”, both Labour MPs in the debate on the Treaty as well as the Labour press supported the Treaty as it offered a way out of the Irish imbroglio and a return to rational class-based politics. The overriding concern of, in particular, the parliamentary leadership of the Labour Party by now was to prove to the British electorate that it could be as protective of British state interests as its rivals. The article argues that that this pragmatic about turn was adopted as many members of the Parliamentary Labour Party (PLP) in particular were acutely aware that the party needed to be seen as patriotic, moderate and responsible if it was to stand any chance of being elected to power. The article traces this reversal in policy by reference to contemporary parliamentary debates as well as through the columns of the contemporary Labour Press. These are the only sources evidencing this change in Labour Party policy. Recent literature on the Labour Party in the 1920s does not address this issue. There is no reference to the Anglo-Irish Treaty either in the minutes of the PLP nor in the papers of the two major players in Labour Party policy on Ireland, the leader Ramsay MacDonald or J. H. Thomas, later Colonial Secretary in the first Labour Government with responsibility for Ireland. [Author]