Nationalism is back, coursing its way through the veins of Europe and other parts of the world. I see it on travels to the central and eastern parts of the European continent – in Hungary, Poland and Ukraine. Those who have seen the BBC Storyville film My Nazi Legacy will have seen me standing in a faraway field in Ukraine talking to people dressed in SS uniforms, men celebrating the creation in 1943 of the Waffen SS Galicia division.

I see it in the United States, from Charlottesville to Wyoming, a country with a president who is able to identify “very fine people” among marchers who wave swastikas, Confederate battle flags and antisemitic banners.

I see it here in Britain, in some Brexit votes and related political developments. The nationalism’s there in Daily Mail and other front page headlines, the ones that describe our judges as “enemies of the people” because they are doing their jobs, interpreting and applying the law with independent minds. It’s there in the views of a prime minister who’d like to leave the European convention on human rights and who told her party conference that “if you believe you are a citizen of the world, you are a citizen of nowhere”.

Those words – bereft of historical understanding – brought to mind a passage from Stefan Zweig’s The World of Yesterday, a book for our times, published posthumously in 1942 after Zweig’s suicide. “For almost half a century,” he wrote, “I trained my heart to beat as the heart of a citizen of the world.” An Austrian passport, he has learned, refers to “more than a patch of territory within set borders”.

Where are we heading? The president of the United States rails against the media and “fake news” (more shades of Germany in the 1930s?), and signs an executive order that would – but for the actions of the federal courts – ban entire categories of individuals and groups from entering the US simply because they are of a particular nationality. Two years ago he called “for a total and complete shutdown for Muslims entering the United States”.

Targeting people not because of their smiles or other individual propensities but because they happen to be a member of a group has a long history. Primo Levi, who spent a year at Auschwitz, made the point in 1947, in If This Is a Man: “Many people – many nations – can find themselves holding, more or less wittingly, that every stranger is an enemy.” When this happens, he continues: “When the unspoken dogma becomes the major premise in a syllogism, then, at the end of the chain, there is the [concentration camp].”

One thing leads to another. Experience – recent experience – teaches us to where such nationalisms can lead, singling out people not for what they have done but because they happen to be a member of a particular group. My family knows to where such a beginning can lead. I found the order expelling my grandfather from the German Reich, in November 1938. He posed no threat to anyone. He could be expelled because he had been made stateless. He was then expelled because of his religion.

How ironic, seven decades on, that the two countries that did more than any other to put in place rules to limit the excesses of nationalism and national sovereignty, recognising rights under international law for individuals and for the protection of groups, have fallen off their perches. How extraordinary, seven decades after the opening of the Nuremberg trial, with its British and American prosecutors and 22 Germans in the dock, that many will look to Germany as the bastion of liberal democracy, as protector of the rule of law, of the rights of refugees and of individuals.

I actually worry less about the United States, with its robust constitution. Over there we see for ourselves the forces of opposition joining to protect basic rights. Brexit, if it happens, is no four-year interlude. Its consequences are far greater – socially, politically, economically and even existentially. Writing my memoir East West Street, I learned how extraordinary was the preparation – by politicians, civil servants, the people – for all eventualities in the course of the war. By contrast, we now know that in the run-up to the referendum no work was done to prepare for departure. I know from my day job as an international lawyer that preparations for a post-Brexit world are wholly inadequate, a pitiful blend of jingoism, nationalism, hope and delusion about Britain’s essential greatness.

All this is nudged along by the poison of slow-burning nationalisms, a desire to “take back control”, in the case of the UK, and “make America great again”. One thing leads to another. Bedazzled by the power of statehood – that most artificial and fake of constructs – are we not also citizens of our home, our street, our borough, our city, our Europe and our world? The reform is clear: to recognise that our essential rights flow not from the happenstance of nationality – and certainly not just from our national passport – but from our essence as individual human beings. That’s what the 1945 moment said, that we are citizens of the world.

We should have, beyond our national passports, a global passport. Over time, the withering of the monopoly power of the nation state, and the oppressive, absurd, monopoly power of the national passport – that would be my reformation.