Using data from the British Labour Force Survey this article provides an empirical investigation of the way immigration affects labour market outcomes of native born workers in Britain, set beside a theoretical discussion of the underlying economic mechanisms. We discuss problems arising in empirical estimation, and how to address them. We show that the overall skill distribution of immigrants is remarkably similar to that of the native born workforce. We find no strong evidence that immigration has overall effects on aggregate employment, participation, unemployment and wages but some differences according to education.