An agreed Brexit deal, an agreed delay in the absence of a deal, and yet another British election to reset things: these all had their turn at feeling likely in the past week. It feels as though by the time this reaches print the UK might not even exist. That was a joke, I suppose. Except it's just a shade too feasible to be funny. So desperately intractable has this become, that the only way Johnson could come close to delivering his Brexit was effectively to give up Northern Ireland as part of the UK in the process. The key element of his now frozen deal with the EU was the establishment of a customs border between Northern Ireland and Britain. It was either this, or put the border in Ireland and risk the return of the awful violence that tore Ireland apart for three decades. Illustration: Andrew Dyson Credit: That is effectively Johnson's choice: set Ireland alight, or sever the UK. He chose the latter, even though he had only recently declared that "would be damaging the fabric of the Union", and that "no British Conservative government could or should sign up to any such arrangement". Brexit makes the most sense when we view it in broad thematic terms that tell us something about this global political moment of upheaval. And the theme that seems most active here is the contradictory nature of nationalism. Brexit lays this bare because it is itself borne of nationalist sentiment, and yet continually falls apart on nationalist terms. It pretends to be a quest for a simple national independence, but is in fact held captive by competing nationalist claims. In this case, those nationalisms aren't the ones that separate the UK from the EU. They're the ones that make up the UK itself.

Brexit's great irony is that it is a political union (the UK) protesting against another political union (the EU) on the grounds that such unions rob its constituent members of sovereignty. Of course, the UK has been reckoning with that problem for years – which is why Wales, Scotland and Northern Ireland have their own separate parliaments. Illustration: Simon Letch Credit: But once you break it down, it's imprecise to say the UK voted to leave the EU. England and Wales did. And even the result in Wales was thanks largely to the retired English people who live there. Meanwhile, Scotland, Northern Ireland and the Welsh-speaking parts of Wales did not. In a very real sense, this was a sovereignty project in which the English sought to impose their will on other nations.

The impossible Northern Irish problem demonstrates this isn't a merely semantic observation. It's a fundamental question of identity in much the same way as the whole Brexit vote was. Suddenly, Northern Ireland and Scotland are being asked whether they're more European than they are part of the UK – because if the Union prevails, it can only do so on England's terms. And the early answers to that question are startling. Loading Replay Replay video Play video Play video Polling conducted by Lord Michael Ashcroft, a former Tory deputy chairman, found that 46 per cent of Northern Ireland would now vote to leave the UK and join the Republic of Ireland – a very high number given the bitter history over this exact issue. Meanwhile in Scotland, Ashcroft found a small lead for those who would vote for Scottish independence. Perhaps England is lucky the independence referendum was done in 2014, before Brexit arose. But now recall that Scotland's First Minister Nicola Sturgeon has demanded a new independence vote by 2021. Anything could happen. Brexit is really a project of English nationalism. And in the very end, there's a slim chance this might be exactly what it delivers: England, alone with Wales. A customs border with Northern Ireland effectively makes it another country immediately, whatever formal descriptions persist. Northern Ireland would almost certainly have to be excluded from UK free trade agreements, for example.

That is a disaster for committed Unionists; that doesn't seem to be true for Tory voters right now who are more committed to Brexit than to the Union itself. Some 59 per cent of them now say they'd prefer to lose Northern Ireland than sacrifice Brexit, and only 28 per cent would choose to call off Brexit instead. The case of Scotland is even clearer: 63 per cent would be happy to see Scotland leave as the price of Brexit. Loading It might just have been simpler if England left the UK. Because the truth is that the British national identity that drove Brexit doesn't exist in the simple way we were urged to imagine. It was always a complicated, contested thing: built on fault lines, existing only in tension. Brexit is the earthquake that has split this open. The only question left is precisely what will survive under the rubble. Waleed Aly is a regular columnist and a presenter on The Project.