What are the origins of today's hostile environment for immigrants in Britain? Using declassified documents from the Foreign and Commonwealth Office, this book tells a secret history of Britain's role in the end of the age of empires in the 1960s. During the post-war period, as Britain made a huge transfer of sovereign power to its former colonies, international demands for racial equality came to dominate world politics. Despite this new international recognition of racial equality, Britain's colonial and Commonwealth citizens from the Caribbean, Asia and Africa were subject to a new regime of immigration control based on race. From the Windrush generation who came to the UK from the Caribbean, and the South East Asians who were expelled from East Africa, Britain was caught between attempting both to restrict the rights of its non-white citizens and redefine its imperial role in the world. Under sustained international pressure, Britain appeared to be poised to make a final transition from a colonial to a postcolonial power, symbolized by its desire to join Europe, which eventually happened in 1973. But Britain's post-imperial moment never arrived, subject to endless deferral and reinvention. Instead officials drew upon an imperial vision of the world to contain what it saw as a vast migration 'crisis'. Citizenship itself was redefined along racial lines, fatally compromising the British Commonwealth and exposing the limits of Britain's influence in world politics. This book reveals an important untold global history of post-war immigration uncovering the origins of the present crisis