BORDER, what border? That was the question posed by the Labour MP Kate Hooey on BBC Radio. “If the Irish want to put up a border”, she went on in Donald Trump mode, “then they can pay for it, because it doesn’t need to happen”. Ms Hooey’s remark has already gone down in Irish folk-lore, like Marie Antoinette advising Parisian bread rioters to eat cake. Perhaps the British will next suggest a border of flowers.

A border does need to happen, of course, because the British Government has made it happen. If you leave a customs union then you have a hard border with countries inside it. And that is not some wily Irish nationalist talking, but the UK Prime Minister herself, Theresa May, in her Lancaster House speech. “Brexit means Brexit” – and Brexit means “taking back control” of trade, immigration and the laws relating to them. That is the definition of a hard border, and its erection is a logical inevitability so long as Ireland remains in the EU customs union and the UK out of it.

This would also, incidentally, be the case were a future independent Scotland to remain in the EU – which is an issue the SNP hasn’t quite got to grips with yet. Some have questioned the wisdom of SNP MPs focusing attention on the Irish border issue since it serves to legitimise Unionist claims that there would be customs posts at Gretna Green after a Scottish independence vote. The SNP position is that an independent Scotland could have a “special arrangement” with Brexit UK, because we already have a common travel area with England and centuries of “friction free” economic and social intercourse. Whisper it, but that’s not a million miles from what Liam Fox and Boris Johnson are arguing about Ireland.

However, there is a very important difference: whatever happens, Scotland and England are not going to go to war over it. Scotland was not partitioned as Ireland was nearly a century ago, with a northern enclave remaining in the UK while the majority of the island became independent. This led to bloody conflict, in various forms, that was only finally resolved by the Good Friday Agreement in 1998. Just because there has been peace in Northern Ireland for the last decade or so doesn’t mean that the troubles could not arise again.

As the Irish Times commentator Chris Jones said, explaining why the Irish Prime Minister, Leo Varadkar, could not sign up to a hard border with the North, the last person so to do was the Irish nationalist leader, Michael Collins. He was assassinated during the Irish Civil War in 1923. Raising the Civil War assassinations might seem like irresponsible alarmism to most British politicians and commentators. Who remembers Michael Collins for heaven’s sake? It’s ancient history isn’t it?

To Britain perhaps, but partition is an inescapable reality in Ireland – one of those ineluctable facts on the ground. The Republic’s three main political parties were defined by the Irish Civil War: Mr Varadkar’s Fine Gael party broadly supported the Free State and the Six Counties, while Fianna Fail and of course the third force, Sinn Fein, resolutely opposed partition. This was all supposed to have been resolved by the Northern Ireland Peace Process. And in a sense it was, but only in the context of a wider European citizenship.

British commentators like to talk about the border issue as a modern version of the Schleswig-Holstein question which Lord Palmerston said was only understood by three people, two of whom had gone mad. But the question of whether Schleswig-Holstein was part of Denmark or part of Germany was finally answered in the only way it could be: by a referendum. And there is a parallel with Ireland. In 1998 there was a referendum in which the North and the South agreed to a peace process, sponsored by the EU, under which citizens of north and south had a new joint identity as citizens of the European Union. This joint citizenship is now being torn up by the UK Government as a result of Brexit.

There has been an unmistakeable air of British imperial condescension over the Mr Varadkar’s threat to veto EU trade talks if there is not a solution to the Irish border issue. How dare a country of barely five million threaten to veto future negotiations on trade between Britain and the EU? But he is right to make a stand. There are only three solutions to the border issue: 1, the UK remains in the single market/customs union; 2, Northern Ireland remains in the single market, thus creating an effective border around the entire island; or 3, border posts. 1 is unacceptable to the Brexiteers, and 2 is unacceptable to the DUP, which holds a whip hand over Theresa May’s minority government.

This means the UK has already decided that there shall be a hard border, even if – ludicrously – some Brexiters think the Irish will pay for it. The border is 315 miles long and there are up to 500 crossing points. Once smuggling gets under way in earnest, as happens on the much less contentious Norway/Sweden border, then HM Customs might rethink this laissez-faire approach. But customs is the least of it.

A confidential paper produced by the British Government for the European Commission (and therefore not redacted as have been the other impact papers) identified 142 cross-border arrangements on everything from children’s heart surgery to foot and mouth disease; from sporting associations to higher education. But perhaps the greatest barrier is psychological. The recreation of a border will undermine the hard-won social cohesion that has arisen since the Good Friday Agreement in 1998.

Police chiefs on both sides of the border have warned that the emergence of border posts, however discreet, will be a target for paramilitary groups, perhaps within weeks of their erection. There is no way of avoiding this: Brexit, and the British Government’s inept handling of Ireland, has set the clock back a hundred years. The tragedy is that the countries of the European Union seem to understand this better than UK politicians.