FOREMOST in the mind of many of those who voted to leave the European Union on June 23rd 2016 was a desire to reduce immigration. Brexiteers had promised that, once shot of the EU and its rules on free movement, Britain could more easily clamp down on arrivals from abroad. Yet in the two-and-a-bit years since the referendum, the government has given away little about how it wants to alter the migration regime after Brexit.

That changed on September 18th when the Migration Advisory Committee (MAC), an official expert panel, published probably the most comprehensive-ever analysis of migration to Britain. Its conclusions, designed to inform government policy, give the strongest hint yet of what the post-Brexit immigration regime will look like.

For most of Britain’s modern history emigration has exceeded immigration (see chart). Yet from the late 1990s immigration rose sharply, first as a strong economy sucked in students, workers and their families from around the world, and then as the EU’s enlargement gave people in the poorer east permission to work in Britain. Annual net migration reached an all-time peak of over 300,000 in 2015-16, shortly before the Brexit vote. The impact of this influx on jobs, housing, the public finances and much else is hotly contested. The 140-page MAC report contains hard truths for immigration sceptics and enthusiasts alike. Migrants do not appear to increase crime and seem to have no effect on the quality of health care, the report finds. Nor do foreign arrivals lead to noticeable rises in joblessness among British workers—indeed, the unemployment rate is at a four-decade low. Migrants also pay more in tax than they receive in public services. Last year those from Europe chipped in £2,300 ($3,000) more than the average adult. Without any migration, Britain’s dependency ratio (the number of over-65s per 1,000 working-age folk) would jump from 285 today to 444 in 20 years’ time. With continued net migration of 250,000 a year, the ratio would be 404.

Yet the MAC also identifies problems. Although migration has little overall impact on wages, it pushes down the pay of the poorest somewhat, while raising that of the better off. Estimates in the report imply that EU migration since 2004 has left the wages of the poorest tenth about 3% lower than otherwise would have been the case, and those of the richest tenth 3% higher. As for the public finances, the MAC is unconvinced that the surplus that migrants produce is always directed to the right places; it also notes that migrants’ contribution could be greater if they were accepted on a more selective basis.

Strawberry fields for not much longer

It therefore suggests a shake-up. Throughout the report the MAC emphasises that different migrants have very different impacts. Highly skilled workers probably raise the productivity of British firms, by bringing new ideas with them. Since they earn more, they pay more tax. Lower-skilled migrants, by contrast, do not hold such clear benefits for existing residents. The MAC worries about the consequences of the enlargement of the EU in 2004, arguing that since then “the scale of low-skilled migration…has been larger than an evidence-based policy would have chosen in the absence of free movement.”

It concludes that, from an economic perspective, there is no reason for Britain to discriminate in favour of EU citizens at the expense of non-EU ones. Better, it says, to select migrants on the basis of their skills or qualifications. The MAC recommends removing the cap on the number of skilled migrants who can be admitted from outside the EU, which stands at about 20,000 a year, not only because it damages the economy but because it “makes little sense for a migrant to be perceived as of value one day and not the next.”

Tighter controls on low-skilled migrants are the flip side of the MAC’s proposal. It recommends ending nearly all such immigration, arguing that low-skilled jobs could be done by Britons or by migrants who come for the purpose of family reunion. (A seasonal workers’ scheme could bail out agriculture, it suggests.)

Some industries predictably squealed at this. The Freight Transport Association, whose members employ migrants as drivers, warned that “next-day deliveries would soon be a thing of the past.” Yet such companies might be forced to invest more in labour-saving technologies, enhancing their workers’ productivity. And having large numbers of businesses engaged in low-wage, low-productivity activities may not represent the best use of Britain’s capital. Industries that have benefited from low-skilled migration are “not necessarily the parts of the UK economy that we want to be growing,” noted Alan Manning, the MAC’s chairman.

The idea of treating EU and non-EU migrants equally seems to align with the government’s thinking. Sajid Javid, the home secretary, has indicated that he would like to harmonise EU and non-EU migration after Brexit. Theresa May, the prime minister, has said she would like “a set of rules for people from the European Union and people from outside the European Union.” The Labour Party also backed the MAC’s proposals, calling for an “end to discrimination” against non-EU migrants.

Yet as the MAC itself repeatedly emphasises, its economic analysis takes no account of the political considerations that surround immigration. The most obvious concerns the Brexit negotiations. The EU would prefer to maintain the free movement of people between it and Britain, since its citizens are the clearest beneficiaries of the current system. In return for preferential access, it might be willing to offer a better trade deal, as well as the reciprocal right for unskilled or retired Britons to live and work in the EU.

The same principle applies to other countries with which Britain hopes to strike trade deals after Brexit. India has made clear that it wants freer migration to be a component of any trade agreement. Last year the then Australian high commissioner suggested that he expected “greater access for Australian businesspeople” as part of the price of a deal.

Mrs May could stick to her guns and insist that immigration policy must be strictly nationality-neutral. In isolation, that might lead to “modest” improvements over the current set-up, as the MAC argues. Yet it would greatly limit the scope of future trade agreements, not just with the EU but far beyond. Not for the first time, Britain must reckon with the fact that taking back control comes at a cost.