Some favour a Hard Brexit, some a soft one, and others claim that the term is meaningless. There is no such dispute about the future of Northern Ireland’s frontier with the Irish Republic. All concerned seem to want a soft border. It’s easy to see why. A soft border is integral to the latter’s political settlement. Furthermore, it has been in place since the United Kingdom and most of Ireland went their seperate ways: there has been a common travel area between the two since 1923. And finally, a hard border is a practical impossibility, as our columnist, Daniel Hannan, has pointed out: “the Irish border is criss-crossed by a latticework of lanes, many of them dating back to public works projects initiated to offer income to local people during the monstrous famine of the 1840s. Even during the height of the Troubles in the 1970s, it was never feasible to man checkpoints along the entire frontier”.

Daniel wrote those words in an article about how Brexit will work after we have a land border with a country that is in the EU, and how it might affect relations between the two. In a nutshell, he argued that neither country is likely to be posed serious problems by illegal immigration and evaded duties after we leave. But since voters and governments will be unwilling to take this for granted, he pointed towards a solution. British customs and border checks could be carried out within Irish territory. Ireland would thus become part of the United Kingdom’s external frontier.

At first hearing, this sounds like an outrageous suggestion – Britain asking Ireland to solve a problem of its own making. However, the idea is already reality, at least to some degree. The two countries agreed in 2011 to develop electronic border management systems and to share data. James Brokenshire made exactly this point to the Guardian earlier this week. The agreement was a sign not only of how closely European governments now work together on border control (outside the EU as well as within it), but also of the unique relationship between the United Kingdom and the Republic. The two are aligned just about as closely as it is possible for independent states to be, and the links are not only economic and cultural but political. Both sets of citizens can vote in each other’s elections when resident in each other’s countries. For example, Irish nationals were entitled to vote here last June on Brexit.

It is true that Britain and Ireland cannot simply negotiate a deal between them. The decision for Ireland is ultimately not in its hands alone but in those of the other EU member states. And while both it and Britain are united in wanting to avoid a hard border with Northern Ireland, those other countries may not automatically see matters the same way. But even if they want to play hardball with Britain, it would be a nonsense for them to do so with Ireland, a fellow EU member and one with which they have no reason to pick a quarrel.

Where there’s a will, there’s surely a way. “We don’t want a hard border between north and south,” Frances Fitzgerald, Ireland’s Deputy Prime Minister, has said. “There is going to be more focus on the perimeter, which we have said all along. We are now the border effectively for the EU.” But the Government will want to handle the matter sensitively. On the one hand, we are entitled to leave the Union if we wish, and the referendum has delivered a verdict to that effect. On the other, the decision has knock-on effects on our closest neighbour – one with which we have a troubled past and a happy present. The details of a Brexit deal over border control will be complex, but the principle is clear. If it imposes new costs on Ireland, then Britain should pay them.