DID Theresa May deliberately sabotage her own Brussels summit on Monday by not first clearing the Ireland border deal with the DUP? She is after all a Remainer. Perhaps it was an attempt to force her own divided party to accept a soft Brexit under which Britain would retain “continued regulatory alignment” with the European Union, as was suggested yesterday by the Scottish Tory leader, Ruth Davidson. For all the appearance of a shambles, was this manoeuvre worthy of a modern Machiavelli? Sadly no. I’m afraid this week’s extraordinary events were more like one of Baldrick’s cunning plans than any stratagem devised by the great Italian diplomat. It reeked of inept diplomatic staff work and uncertain political leadership. Worst of all, it betrayed an ignorance of Irish history. The UK Government seems unable to get its head round the problem of having a land border with the EU in Ireland, and persists in regarding it as a mere technicality – something dreamed up by Brussels to wring more money out of the UK.

Yet Jean-Claude Juncker was more than happy with the putative British-Irish deal on Monday and wanted to go full steam ahead into post-Brexit trade talks. It was Mrs May who had to break off her lunch with the EU president to take a call from the DUP leader, Arlene Foster, telling her that Ulster said no. It beggars belief that the UK Government had taken the deal to Brussels without having cleared it first with its own coalition partners. EU diplomats, when they stop laughing, find this incomprehensible.

The confusion risks setting Irish politics back a century. There were harsh words yesterday from the Ulster Unionists, accusing the Republic’s Taoiseach, Leo Varadkar, of over-reaching himself and trying to drive a regulatory wedge between Northern Ireland and the rest of the UK. There are long-held unionist fears that Dublin is trying to unite Ireland by stealth by creating a de facto border in the Irish Sea. Mr Varadkar says he has no such intentions, and assumed that when he was striking a deal with Mrs May, which involved concessions on Dublin’s part, he was dealing with the entire UK and not just one part of it.

Mr Varadkar accepted a toned-down version of his earlier demand that there should be “no regulatory divergence” between the North and the Republic after Brexit. That might, in effect, have required Northern Ireland to accept the regulations of the European single market in perpetuity. So, last weekend, he accepted the looser phrase “continued regulatory alignment” proposed by Number 10. Mind you, the Irish Foreign Minister Simon Coveney said that he didn’t recognise any difference between alignment and convergence, and suggested that the North would effectively be remaining, if not actually in the EU single market, then certainly compliant with its trading rules in future.

The UK view is that this is not the case. It believes “alignment” means only that attempts will be made to keep regulations broadly in line with Brussels, and, moreover, only in the areas that are covered by the 1998 Good Friday agreement and the Irish peace process, namely, transport, agriculture and energy, not trade in general.

Number 10 has been too clever by half here. Setting up border posts and creating a hard border could never be reconciled with the Irish peace process, even if an open border was not specified in the text of the Belfast Agreement. It didn’t need to be. Free movement of goods, services, capital and people was taken as read, because both north and south were in the single market, and crucially the peace process was sponsored by Brussels.

There’s no way round this. If Britain is leaving the EU there must be a border somewhere – either in the North Sea or between Northern Ireland and the Republic. The only alternative would be for the UK as a whole to remain compliant with the rules of the European single market. Enter the Scottish Tory leader, Ruth Davidson, saying: wotcha, why doesn’t the UK do precisely that and retain regulatory alignment with the EU? Job done.

Nicola Sturgeon agrees. Britain could seek a deal similar to that of Switzerland or Norway, neither of which is in the EU but which accept the rules of the single market. Norway is not in the EU customs union either, which means it can negotiate its own trade deals. This seems to be the only way of squaring the circle and preventing the restoration of a border between Ireland and the UK.

However, Brexit Tory MPs like Jacob Rees Mogg aren’t having any of it. They regard such half way houses as EU membership by another name and the Brexit Secretary, David Davis, appeared to agree with him yesterday. The Brexiters have lined up with the DUP to reject all such “remoaner” backsliding. Remaining in the single market, or aligning with it in perpetuity, they believe, could mean the European Court of Justice still having a say in British laws. They want to use this DUP crisis to achieve their dream of a no-deal “clean Brexit” in which Britain tells

Mr Juncker and co to sod off and the UK reverts to WTO trading rules.

Mrs May has had little to say on this most crucial issue of her premiership. One suspects that some kind of fudge will be agreed by the DUP later this week. But it will not resolve the border issue; nothing can. It is simply the logic of Brexit. The UK can keep saying, “I see no border”, as long as it likes, but it won’t alter that reality. Only real leadership from Number 10, perhaps along the lines proposed by Ms Davidson, could salvage Brexit from this semantic and constitutional imbroglio.

Ms Sturgeon has been calling for a broad cross-party coalition to keep Britain aligned with the single market. A gifted political leader might see a way forward here, and even a way of reinventing the Union itself, by marginalising the Tory hard right. But Mrs May is neither gifted nor in charge of events. She appears like a PM on autopilot, and there’s no one else around to take over the controls and make a soft landing.