BBC political editor Nick Robinson sets out to test what has actually driven decades of immigration into Britain, from postwar arrivals by sea and air to the anxieties surrounding a new wave from Eastern Europe. He examines government pledges to crack down on illegal immigrants and send them home, and revisits the political predictions that Romanian and Bulgarian arrivals would flood the country, a surge that never materialized. Robinson questions politicians and looks at the decisions behind what he calls the biggest immigration surge in modern history, asking whether any government ever really controlled it or merely reacted to it after the fact. The film also weighs the economic case, tracing how immigrant labor helped build British prosperity, against the political backlash now threatening to reverse it. Robinson treats the panic itself as part of the story, noting Britain's history of overblown immigration scares, and closes on the open question of whether that backlash could end up damaging the country it claims to protect.