Illegal immigration is likely to rise when Britain leaves the EU and freedom of movement ends, a new study has found.
The report by the Social Market Foundation said closing legal migration routes after Brexit would lead to more people trying to enter and stay in the UK illegally.
It said politicians who claim that Brexit will solve public concerns about immigration should “come clean” about the actual consequences of ending free movement.
Failure to do so would result in a backlash when voters realised that leaving the EU had not solved their fears about immigration, and risked “creating the sort of conditions in Britain that helped Donald Trump become US president”, the SMF said.
The study analysed previous cases where immigration was restricted and entry policies tightened, including Britain ending unrestricted migration from Commonwealth countries in the 1960s and the US stopping a programme for Mexican workers in 1965.
It found that stricter controls on immigration often led to an increase in the total number of migrants in the country, because people who could previously travel back and forth easily instead opt to stay.
Greater restrictions also fuel an increase in illegal migration as people who would previously have entered the country legally instead do so through other routes.
The SMF predicted that the number of people living in the UK illegally would increase after Brexit, as EU nationals who have not been given the right to remain in the country decide to stay without permission.
It called on the government to “inject a dose of honest realism, coming clean about the complexities and unintended consequences of immigration policy, about the control that it does have, but also the practical limits to that control”. Read more