26/11/2015 15:10 GMT | Updated 26/11/2016 05:12 GMT

The Net Migration Target: People Are coming, But They're Not Leaving

Today the government released the latest update of the net migration target. The figures show that net migration to the UK was an estimated 336,000 in the year ending in June 2015. That is the highest level on record. It is also more than three times the government's official target.

The net migration target is a game of two halves: it subtracts the number of people arriving in the UK from the number of people leaving. The figure continues to rise because the number of people arriving is increasing steadily while the rate of those emigrating from Britain has remained stable since the economic crash in 2008. To get the net migration figure down to its target, the government needs the number of people arriving to fall and the number of those leaving to rise.

Indeed, the immigration minister James Brokenshire said as much, when he blamed today's rise in net migration on foreign students not leaving at the end of their courses. Unfortunately for Mr Brokenshire, his policies may in fact be discouraging emigration.

The evidence suggests that toughening restrictions on people coming into a country reduces both immigration and emigration. The reduction in inflows that is achieved by restricting visas is almost cancelled out by discouraging those who are already here from emigrating. A perverse incentive takes hold, where the risk of not being allowed back encourages people to stay put.

This is basic human psychology: investing in something (for example applying for, paying for and obtaining a visa) means you will think carefully before you surrender it. Someone who queues for a long time to get into a bar or restaurant will be loath to leave if they are unsure what the offers elsewhere are.

This predominantly applies to non-EU immigrants, most of whom need a visa to work or study in Britain. Today's statistics show that fewer immigrants from non-EU countries are leaving Britain for work abroad. But it is also possible that the upcoming referendum is having a chilling effect for EU immigrants too. EU nationals currently have the right to move freely to another EU country to work or study. Brexit would change that - so people who are here now may be thinking twice before going back home.

That does not mean the government should scrap all restrictions on people coming to the UK, in the hope that might encourage them to leave. That would patently be nonsensical. But the government could be clearer on who it wants to incentivise to stay.

Currently, foreign students who have spent years learning in English, building relationships and understanding British culture are kicked out at the end of their course. That is rather counterproductive, because, as we argue at IPPR, that kind of integration is what makes immigration work.

Today's statistics are little more than a useful reminder that immigration policy is complex, full of unintended consequences, perverse incentives and changing patterns of human behaviour. It might feel simpler to boil everything down to one big number. But immigration, dealing as it does with human life, is much more complex than that.

In truth, the net migration target is far too blunt and crude to be much use to anybody. The target lumps together refugees fleeing ISIL with entrepreneurs from the US, cleaners from Poland and students from Hong Kong. It will never offer a sophisticated or useful snapshot of the state of immigration in Britain, other than to testify that it exists.