The UK’s flailing effort to leave the EU can be measured not in policy gains or political successes, but in soundbites. It is best captured in the one beloved of Boris Johnson, Britain’s foreign secretary, that, when it comes to Brexit, “we can have our cake and eat it”.

Johnson, who is due to visit Dublin on Friday, will no doubt be offered tea and – who knows? – cake when he meets Simon Coveney, the Minister for Foreign Affairs, at Iveagh House. As even the British foreign secretary must know by now, though, having your cake and eating it is not a sustainable foreign policy.

It has taken a while, but that reality is beginning to sink in among Britain’s arch-Brexiteers, of whom Mr Johnson is the blustering archetype. To take one example that concerns us mightily in Ireland, consider the breezy response of British advocates of leaving the EU to Irish concerns about the impact of Brexit on the Border. What we were told repeatedly was, in effect, “Don’t worry, nothing will change”.

There was no better illustration of the Brexiteers’ cluelessness about Ireland than that obvious falsehood. The ignorance was instructive, nonetheless. Dominic Hannigan, who was the chairman of the Oireachtas EU affairs committee before the UK referendum, told me, after an appearance by – I think – Bill Cash, another arch-Brexiteer Conservative MP: “The trouble with the British is that they think we are still part of the family.”

Knowing nothing about Ireland is hardly new among British political leaders. That may have something to do with the poor state of history-teaching in English schools. Johnson and other arch-Brexiteers such as Jacob Rees-Mogg, who has emerged as the darling of the Tory right wing, went to Eton and the University of Oxford. They received the best education money can buy. Yet they seem to have learned nothing.

That is one reason why the dangers of Brexit for the island of Ireland – for not just economic ties but social, historical and political affiliations, in some cases dating back centuries – were so casually brushed aside before the referendum. A campaign based on “taking back control of our borders” had nothing to say on the post-Brexit fate of the UK’s most important external border – the one that separates this Republic from Northern Ireland.

Clean break

There is more to the Brexiteers’ attitude to Ireland than mere cluelessness, however. There is the awful prospect that they simply do not give a damn. Their desire for a clean break with the EU, their readiness to reverse nearly half a century of assimilation in European networks of trade, diplomacy and security, and their willingness to turn their backs on the world’s largest and richest free trade zone in the stated pursuit of free trade, are evidence that they don’t really care about Britain or Europe. Why, in the circumstances, should they give a fig about us?

Yet, as was evident after last week’s round of negotiations between the UK and the EU, nowhere is the wishful thinking at the heart of Brexit being exposed more pitilessly than on the question of the Border in Ireland.

The Brexiteers tell us at every opportunity that there must be “no hard border” in Ireland after Brexit. Yet the strategy they are maniacally pursuing, of a “cliff-edge”, or “hard”, or “no deal” Brexit, will create that very thing, with all the administrative, physical and political infrastructure that will be required to make it work. That is the political and legal reality of the UK’s decision to leave the EU single market and customs union, and not a plot by eurocrats to punish Britain. The argument by pro-Brexit advocates that if there is a hard border in Ireland after the UK leaves the EU, it will be the fault of Europe and not the UK, is dishonest.

Human tragedy

Why do Brexiteers hold such a contradictory stance on the Irish Border? One answer is that they do not understand the nature of borders – and in particular the nature of the Irish one. They seem to regard the Border as simply a commercial barrier that can be overcome with the use of (yet to be invented) technological wizardry; as a 500km-long traffic-calming speed-bump that you can negotiate just by slowing down for a minute.

Of course, the Irish Border is a commercial barrier. It divides two economies that use different currencies, for starters. Uniquely in the EU, however, it does not divide two peoples made distinct by language, religion or history. It is happily disappearing for practical purposes, but it remains a political, symbolic, historical, psychic and contested space. As I discovered last spring, when I spent a few days in Fermanagh talking to people whose lives were changed forever by their proximity to the Border, it is a place of human tragedy and ethnic cleansing.

The Brexiteers are ignorant of the Border – not just of its symbolism but of the reality of life along its winding course through communities, fields, and farmyards. That is why they appear ready to sacrifice the spirit, if not the letter, of the Belfast Agreement, with all its imperfections, its cumulative small victories, and its one great achievement, in their pursuit of a fantasy that does not include us.

Yet their ignorance has set a trap for them. Our Brexiteer friends are starting to discover that it is not in Brussels or Berlin that they cannot have their cake and eat it, but in Ireland.