Brexit Britain might not always feel like a supportive place for migrants or supporters of migration. Every day brings new stories of suffering and injustice meted out to migrants by a callous government. Demands for restrictions on migration have disrupted politics for a generation, culminating in the vote to leave a European Union that many voters had come to see as part of the migration problem.

Yet Brexit Britain is also a country where the public is more positive about migration now, after the largest sustained inflow of migrants in the nation’s history, than it was when the change began. A country where public outrage against the unjust treatment of long-settled migrants by the national government has just forced the resignation of a home secretary.

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The conventional wisdom in many liberal circles holds that Britain has turned in on itself, encouraged by a Leave victory that has legitimated chauvinism and xenophobia. Yet the public opinion evidence consistently shows the opposite – the British are more open to migration than ever, a trend that Brexit has encouraged, not reversed.

Only around a quarter of survey respondents saw migration as good for the economy in 2002, before the admission of new EU members produced a surge in European migration. By 2014, with support for Ukip at its peak, the figure had risen to four out of 10. It has risen further since. More British people also think of migration as enriching British culture now, after 20 years of unprecedented migration inflows, than felt this way in the early 2000s, when the current wave of migration was just beginning.

The public today is also less likely to name migration as a political priority. This “salience” measure is a powerful predictor of voter behaviour – it was those most worried about immigration who switched to backing David Cameron’s Conservatives in 2010 following their rash pledge to cut migration to the tens of thousands and switched again to Ukip a few years later when the Conservatives failed to deliver.

For more than 15 years, between a quarter and a half of poll respondents have spontaneously named immigration as among their biggest political concerns. Yet since Brexit, complaints to pollsters about immigration have collapsed. More than 40%of respondents in Ipsos Mori polls named it as a key issue in the run-up to Brexit. That figure has slumped since and now stands at under 20%, a 15-year low.

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This collapse in concern about migration is puzzling, as there have been no major changes in migration policy since Brexit, and though migration levels have fallen, the decline has been modest. It is perhaps just as surprising, given the conventional wisdom that the British are intrinsically hostile to immigration and Brexit has exacerbated this, that positive views about the effects of migration are steadily rising – a rise which Brexit has not reversed but accelerated.

The role of fairness offers one possible resolution to this puzzle. The British are not, in fact, intrinsically hostile to migrants or blind to the benefits migration can produce. But they do have a basic sense of what a fair system looks like – and react very strongly against anything that breaches that fairness instinct.

The most powerful anti-migration media narratives have mobilised this fairness instinct against migrants. In the early 2000s, public hostility to asylum seekers was stoked by a belief that most were not genuine refugees, but economic migrants exploiting British generosity. Later, the focus shifted to Britain’s welfare system – with regular stories of migrants coming to Britain to claim generous benefits despite not having paid in.

The perception that the extension of EU free movement rules violated fairness principles by conferring rights without attaching responsibilities may similarly be one factor in the recent unpopularity of EU migration and the belief that the Brexit vote has made the public desire for rules and order clear to politicians may be one reason for the recent sharp decline in concern about migration.

The biggest migration stories since Brexit have mobilised the fairness instinct in the opposite direction. We first saw this with the debate over EU citizens’ rights. Just months after a divisive referendum in which EU migrants had featured prominently, polling revealed overwhelming public support for an immediate guarantee of full rights for all EU migrants resident in Britain. Basic principles of fairness led people to this liberal conclusion.

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The public recognised that people who had come and built lives in Britain with an expectation that they would be able to remain for as long as they wanted should have that expectation respected by government. The fairness instinct was also at the heart of the outraged public reaction to the Windrush scandal. Those who came to Britain as children, on British passports, had an obvious and justified claim to fair and equal treatment from the only country they had ever known. Their treatment as interlopers and criminals was a flagrant violation of these basic principles. Windrush revealed to politicians that the British will turn on a government they think isn’t playing by the rules with just as much fury as they turn on a supposedly exploitative asylum seeker or welfare claimant.

The liberal shift in public opinion has come together with a groundswell of opposition to the unfair treatment of settled migrants at exactly the moment when a new home secretary, Sajid Javid, himself a child of migrants, sets out to build a post-Brexit migration system. This is a powerful opportunity for supporters of migration to entrench principles of openness and fairness.

Steadily growing recognition of the economic and cultural benefits of migration makes the case for opening Britain to the world’s best and brightest students and workers easier to make. The public demand for fair treatment of settled migrants can be channelled into new proposals to entrench their political and social rights. There is very broad support for this – large majorities from all walks of life favour giving settled migrants who play by the rules full political and social rights after between three and five years – including majorities of those who are most sceptical about migration in general. Migration supporters should also push for deep cuts to the extortionate fees imposed on migrants seeking to confirm their status and rights – fair treatment should be a matter of right, not means.

The Windrush crisis has shown that a migration system that has violated basic principles of fairness is no longer tenable. We should seize the chance to build something better.

• Robert Ford is professor of politics at Manchester University