Among the imponderables of Brexit, one seems little discussed: what will the UK’s migration policy will look like outside the EU? Not least because the provision of visas may be a factor in any deal with India and Australia.

During the referendum, prominent leave politicians insisted that their campaign wasn’t motivated by xenophobia. Remain campaigners insisted it very much was. We’re about to see those two theories put to the test on an issue that has wide implications for the UK’s future, and even perhaps whether Brexit happens at all.

If Theresa May is serious about the UK’s future as a global nation, open to the world and treating other countries as equals, there’s a way for her to prove it.

As an EU member, Britain has open access for the predominantly white citizens of its member countries. A German migrant to the UK can live and work here by right and bring in friends and relatives for visits as they please. As minority ethnic communities can testify, it’s usually a very different story for them. Even arranging a visit for a relative from outside the EU means jumping through all kinds of hoops, substantial costs and no guarantee that a visa will be issued.

It would also be advisable for the government to ask itself: can it really afford to blithely antagonise minorities?

If this government means what it says about a global future, it could announce that, post-Brexit, every other country’s citizens can expect equal treatment regarding access for work, study and visits. The details of any migration policy aren’t important – this principle is.

Making that clear from the beginning would not only prove the government’s good faith but also make negotiations with other countries a lot easier. The Indian government won’t be impressed if it discovers that a disparity exists, and that Australian citizens can expect more generous treatment from the UK than their own can.

This isn’t just a matter of other countries seeking the best for their own people; it’s also a question of self-respect, always an important issue for countries that historically were victims of imperialism.

But – and this may have more traction in these cynical times – it would also be advisable for the government to ask itself: can it really afford to blithely antagonise minorities?

The smarter remain activists now realise that insulting their opponents is futile. It didn’t work before and it won’t now. So instead, they’re eyeing up what is an often contradictory coalition of leave voters with a view to breaking it up and maybe reversing the decision. One element of that leave coalition is the black and minority ethnic (BAME) vote, as it’s a seemingly intractable myth that ethnic minorities were solidly remain.

The London borough of Newham is one of the most multi-ethnic in the country where the white British form about 15% of the residents. It did indeed vote remain, but only by about 6,000 votes. Like the rest of the population, ethnic minorities voted one way or another for a combination of reasons (good and bad).

Why do some ethnic minority voters want to leave the EU? Read more

For what it’s worth, I voted to leave. Several remain MPs have told me that during the referendum the subject of differential treatment for migrants from the EU as compared to that endured by those from other parts of the world constantly cropped up in discussions with BAME communities. Indeed, they were assured that one of the benefits of Brexit would be a closer and more straightforward relationship with the Commonwealth. But if that was a deception, if what we are to have instead really is a recreation of the old kith-and-kin policy, which prioritised migration from primarily white countries, minority leave voters may well decide their concerns aren’t being addressed by Brexit, and might sensibly defect to the other side.

Will that matter to the government as it presses ahead with an article 50 vote and Brexit? It will and it should. For at some stage over the next few years, it’s inevitable that May’s negotiations with the EU will run into serious trouble. She can threaten a harsh, abrupt, cold-turkey sort of Brexit all she likes, but she must know of the risk that less committed leave supporters will flake away. The more who switch, the more difficult her position. A people so obviously betrayed could switch very easily.

It would be nice if the government were to promise equality for the rest of the world on migration and visas as a matter of moral principle. Moral principles matter, even in these fractious times. But if that’s too big an ask, perhaps the government could do the right thing for its own sake. If they don’t have to make enemies of minority Brexiters, why do it?