In this ground-breaking book, the author draws extensively on archival material and theortical advances in the social sciences literature on citizenship and migration. Citizenship and Immigration in Postwar Britain examines the transformation since 1945 of the UK from a homogeneous into a multicultural society. Rejecting a dominant strain of sociological and historical inquiry emphasising state racism, Hansen argues that politicians and civil servants were overall liberal relative to a public, to which it owed its office, and pursued policies that were rational for any liberal democratic politician. He explains the trajectory of British migration and nationality policy - its exceptional liberality until the 1950s, its exceptional restrictiveness after then, and its tortured and seemingly racist definition of citizenship. The combined effect of a 1948 imperial definition of citizenship (adopted independently of immigration) and a primary commitment to migration from the Old Dominions, locked British politicians into a series of policy choices resulting in a migration and nationality regime that was not racist in intention, but was racist in effect. In the context of a liberal elite and an illiberal public, Britain's current restrictive migration policies result not from the faling of its policy-makers but those of its institutions.