This thesis contributes to one of the main debates of British imperial history, the relevance of the Empire to British society. It examines a number of twentieth century imperial activist groups and discusses in detail the Junior Imperial League and the League of Empire Loyalists. It argues that the Junior Imperial League was an important imperially-minded organisation which gave valuable practical support to the Conservative party. It suggests that the imperialism of the League of Empire Loyalists had ideological roots in the imperialist ideas of the late nineteenth century has been overlooked by historians who have perceived it as relevant only to extreme right-wing politics. It suggests that both these groups have been given too little, or the wrong kind of, attention by historians. The first has simply been overlooked and the second has tended to be subsumed into a search for British fascism rather than studied as a specifically imperial body. The analysis of these two groups, in the general context of imperial group activism, hints at a reading of British imperial consciousness that it more subtle than the one in much current literature. Imperialism was neither ubiquitous nor non-existent. A substantial number of activists in Britain in the first half of the twentieth century, estimated to exceed a million, cared about the Empire in various ways and with a range of intensity. Members of imperial activist groups came from all classes, although the leadership of imperial activism was often upper-class. However, imperialism mattered most when it was most ‘banal’ and most intertwined with a broader political Conservatism. Members of the Junior Imperial League rarely saw their imperialism as controversial or something separate from their broader political vision. They associated it with the governance of the Empire, its defence, trading relationships, education, and Anglo-Saxon feelings of ‘kith and kin’. The League of Empire Loyalists revealed a different pattern of imperialism at a time when empire had become much more contested. The LEL mobilized people who saw empire as the salient feature of their own political identity. In many ways their central concerns were similar to those of the Junior Imperial League but their sense of their marginality revealed how far empire had moved from the mainstream of British politics.