Not only were the Brexiters clueless: they didnt give a stuff about Ireland. But this will come back to haunt the Tories

Donald Tusk should be criticised not for his malice, but his moderation. The European council president triggered a tsunami of confected outrage from leavers today when he observed, with some justice, that there should be a special place in hell for those who promoted Brexit without a plan. But he should have said far more. He should have added that, within that special place, there should be an executive suite of sleepless torment for those politicians who promoted Brexit without ever giving a stuff about Ireland.

Once again, Brexit is all coming down to Ireland. This was always going to happen, and rightly so. Time after time in our history, Ireland emerges as an awkward reality check that shames the fantasies of those who think the British are better and that Ireland can be ignored. So there is something both fateful and tragic about the fact Theresa May should have prepared for the final showdown by having to make a rare visit to Ireland.

It wasnt meant to be this way. For the Brexiters, the leaving of Europe was never about Ireland at all. Brexit was about sovereignty, about greatness, or about not liking too many foreigners living here. It was about throwing off the yoke of Brussels and bringing back blue passports. Ireland barely got a look-in during the debates of 2016, save when John Major yawn, yawn and Tony Blair hiss, boo pointed out from lifetimes of experience that Brexit would threaten the Northern Ireland peace agreements.

Their warnings fell on stony ground, except, not irrelevantly, in Northern Ireland itself, where the majority voted to remain. This was a deeply embarrassing outcome for the Brexiters. Surely a place that wraps itself in the union jack so often would be full-hearted for a Brexit project that did exactly the same? When the Northern Ireland voters failed to oblige, the Brexiters did what fantasists do. They pretended that it hadnt happened. In this, they were of course assisted by Mays decision, after the 2017 election, to make a pact with the Democratic Unionists, the only important Northern Ireland party to support leaving the EU.

Then came the backstop, designed to prevent a hard border, which is now incorporated into the withdrawal agreement. The political intimacy that has grown up in recent months between the Tory Brexiters and the DUP might lead the unwary to assume they look at the issues in the same way. But they do not, as the backstop repeatedly shows. It is an opportunists alliance, nothing more, nothing less. It cannot and will not hold.

The DUP hates the backstop because nationalists support it. They pretend that it could cause regulatory divergence between Britain and Northern Ireland though they support divergence on issues such as criminal law and some tax issues. They see Dublins hand at work everywhere. But the DUP did not get where it is today by compromising with Irish nationalism. So, if Sinn Fin and the SDLP in the north are in favour of the backstop, and if Dublin is in favour too, then the DUP is hardwired to be against it. Their position is tribal.

The Tory partys Brexiters are not tribal so much as fanatical. They are a mix of English nationalists and trade autonomists. They hate the backstop because it gets in the way of their deregulatory obsession conveniently ignoring that the EU is in fact a free trade market. For the Brexiters, the Irishness of the backstop is incidental. For the DUP it is everything. While the DUP is trying to preserve Northern Irelands place in the UK, the Brexiters dream of global conquest.

That is why Mays visit to Northern Ireland is part of a forlorn effort to unite her party behind a tweaked withdrawal agreement that still contains a backstop. In Belfast this week she gave the game away. Im not proposing to persuade people to accept a deal that does not contain that insurance policy for the future, were her words. Today it became clear that May is not relying on a technological fix on the border, not least because of nationalist sensitivities. Northern Ireland businesses liked what they heard. The Tory Brexiters did not. There were fresh calls to bin the backstop, and renewed threats to vote down any deal of which it forms part. David Davis, inevitably, said hed be able to get things sorted quickly if he was in charge.

It would be foolish to assume May has no chance of marshalling a narrow Commons majority behind some version of her EU deal next week. But the odds remain long because she wants to do the right thing, more or less, in Ireland. This has always divided the Tory party down the middle, since the era of Robert Peel. And as Peel found out, it was difficult for a great Tory leader, never mind a limited one.

In 1846, Peel came to the House of Commons to propose the repeal of the corn law tariffs on imported grain. Much of his Tory party, which represented landed interests in the areas where British grain was grown, would have nothing to do with his plan. Peel was a pragmatist: he only became a repealer because events demanded it. Those events were the Irish potato blight and famine. The decision to repeal broke the Tory party for a generation.

Peel could, he admitted to MPs, have concealed the seriousness of the situation in Ireland by rousing the British lion or adhering to the true blue colour. But the suffering of four million people in Ireland was too serious, and would only increase. Peel read out a series of shocking eyewitness accounts. It is absolutely necessary, said Peel, before you come to a final decision on this question, that you should understand this Irish case. You must do so.

It was a speech his critics could have dismissed, if the phrase had been in currency, as project fear. It was, in fact, project national interest. Some time next week, May is going to face a similar challenge. Britain in 2019 is not Britain in 1846. The issues faced by Peel and May are very different. But Conservative MPs still face the same question the need to understand the Irish case.

Martin Kettle is a Guardian columnist