Theresa May, Britain’s home secretary, has barely disguised her ambition to succeed David Cameron as Conservative leader. To achieve this, she has worked hard to burnish her credentials with the Tory right. This has sometimes led her to take positions that appeal to backbench MPs but are much harder to square with Britain’s economic interest.

Immigration is one issue on which Ms May has allowed personal political tactics to trump sensible policy. The latest sign of this is a proposal that emerged from her office over the weekend regarding foreign students who have graduated from British universities and want to work in the UK.

As is well known, the principle of free movement across the EU means the UK can do nothing to stop European citizens working in Britain. If they are to cut migration, the Conservatives therefore must restrict entry for people from outside the EU. Hence, students from India, China and the Middle East are increasingly in Ms May’s sights.