There are now a million undocumented - or ‘illegal’ - immigrants in Britain, many of them settled here with families. When Boris Johnson edited The Spectator, he argued that an amnesty should be offered to those who have been here for a long time. He retained the policy as London Mayor. Is it now time for him to implement it? Would such an amnesty be a bold expression of liberal conservatism - or a dangerous weakening of Britain’s borders and security?

Hear Fraser Nelson and Kate Andrews, the Spectator's Economics Correspondent, debate David Goodhart, head of immigration at Policy Exchange, and Alp Mehmet, chairman of Migration Watch UK.

Moderated by Katy Balls.