The author draws extensively on archival material and theortical advances in the social sciences literature on citizenship and migration to examine the UK's transformation, since 1945, from a homogeneous into a multicultural society. Rejecting a dominant strain of sociological and historical inquiry emphasizing 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.