Concerns over immigration levels were central to the Brexit vote and are now dominating the debate in the lead up to the UK general election. Meanwhile, controversies over irregular migration are spreading throughout Europe – in Italy, they headline front pages, and in Germany, they are likely to play a big part in determining the future of Angela Merkel.

Much of the debate revolves around how best to control immigration levels. In the UK, the focus is on the net migration target and the end of free movement: is it a good idea? Can it be delivered? Will fewer migrants harm, or benefit, the British economy and society?  

Just last week it was announced that net migration to the UK has fallen below 250,000 for the first time in three years. The government welcomed this as ‘good news’. However, many commentators warned that this was due to EU citizens leaving, rather than fewer people arriving, with potentially negative effects on the UK economy.

So how much will it cost to reduce the number of immigrants, and will it be money well spent?

When asked about the cost of reducing immigration, politicians tend to dodge the question, partly because they genuinely don’t know the answer, partly because the answer may not be what the voters want to hear. A recent poll found that, in the UK, voters are keen to see migration from the EU reduced but only if free or cheap, even amongst those who voted to leave the EU. 

Yet reducing immigration is neither free nor cheap. While the real costs are not always easy to estimate, the evidence suggests that reducing immigration is potentially an expensive promise to keep, with a very uncertain outcome.

ODI research estimates that EU governments have already spent at least €17 billion trying to protect their borders and reduce irregular migration, with very mixed results. While Syrian refugees may no longer be landing in Lesbos in the hundreds of thousands, irregular migration from Africa to the EU has remained pretty constant over recent years. If anything, it is set to increase because of demographic trends. The IMF estimates that by 2035, the number of sub-Saharan Africans of working age will exceed that of the rest of the world combined.

Despite these trends, a significant amount of money is being spent in an attempt to control borders and enforce security: the UK is projected to spend £558 million in 2016/2017 to patrol its borders, including £50 million in Calais alone. According to the Office of Budget Responsibility, by 2020/2021, reducing immigration will cost the UK approximately £6 billion.

The costs of reducing immigration are far wider than fences and police dogs. Across Europe, imposing border controls in areas that have previously enjoyed free movement will have both short and long term impacts on the economy and society.  For example, reintroducing Schengen borders could cost France €1 to €2 billion in increased transport costs, reduced tourism and impacts on cross-border workers; and €10 billion in lost trade. Across the EU, the wider cost of reducing immigration could be anywhere between €470 billion and €1.4 trillion.

If we add together the direct costs of reducing immigration, these wider and longer-term costs, and the losses in productivity and other benefits, UK voters stand to lose an awful lot more from immigration control that politicians are prepared to admit.

Voters should not be made to believe that reducing immigration is a zero-sum game. We should scrutinise politicians on the costs of reducing immigration like we do for any other manifesto pledge. We should be told where the money is going to come from, what the fiscal consequences of these choices are, and what else will need to be cut to deliver on the promise of controlling immigration. If they cannot deliver, we should hold them to account.