I’m afraid Brexit has always been about Ireland. Perhaps Salzburg will finally, brutally, illustrate that point. The Spectator declared its support for Leave in the final week of the 2016 referendum campaign. The editorial arguing in favour of a leave vote hinged not on free trade, but sovereignty: which is a different way of saying control. It did not mention Ireland at all – but very few did. It was of marginal interest.

I read that leader in Downing Street, where I then worked. I did not then, and do not now, agree with the sovereignty argument – but I can respect it. Since EU membership necessarily involves compromising on pure national sovereignty, it follows that a vote to leave offers the opportunity to reclaim some sovereignty. That is at least a better reason to leave than the proposition that exiting the world’s largest free trade area will offer the UK the opportunity to trade more, which is daft.

The problem is what to do with the sovereignty that is being reclaimed so painfully. In particular what to do with it in relation to Northern Ireland. The UK is the sovereign Government in Northern Ireland, but there is a ‘but’. The Irish government has a formal right to be consulted on the governance of the region; its citizens have the right to identify as British, Irish or both. It is the only part of the United Kingdom where citizens have both a permanent legal right to EU citizenship, and a formal route back to EU membership via a future referendum on Irish unity.

So British sovereignty – or control – in Northern Ireland is qualified. It is the qualification of that sovereignty via the Belfast Agreement which has enabled the Irish Government to insist upon the now-famous ‘backstop’, an insurance policy to avoid goods checking on the island of Ireland and a so-called ‘hard border’. But British sovereignty is only qualified, it is not removed. The UK can choose to assert its sovereignty by rejecting the backstop. That will be Parliament’s right when a withdrawal deal is put before it, if indeed a deal can be concluded, as looks slightly more unlikely after this week.

Received wisdom among Britain’s political class – even among Remain supporters – has long been that the UK’s unique history and geography rendered the European project at least partly incompatible. That the UK did not have a comparable history of territorial dispute or contested sovereignty in the 20 th

So it should be no surprise that the biggest obstacle in leaving an international organisation founded in part to avoid territorial conflict between its members is the fate of a region where for most of the 20 th

The Irish constitution of 1937 claimed sovereignty over the whole island – an open sore for Ulster’s Unionists for many decades. That claim was removed in 1998, replaced by clarity over Northern Ireland’s constitutional position, but also a say for the Irish Government and a formal mechanism for leaving the UK. This was the Good Friday, or Belfast, Agreement, which performed the curious trick of softening British sovereignty in Northern Ireland while simultaneously strengthening the Union with Britain. Believe it or not, it strengthened the union because it softened sovereignty. Nowhere is this truer than on the border itself.

Northern Ireland is that kind of place: ambiguous. Hard assertions of sovereignty, or control – from Dublin or London - have not tended to serve the place especially well. Nor have they served Unionism well. Liberal Unionist Joseph Chamberlain, once touted as the philosophical antecedent of Prime Minister May, scuppered Home Rule for the entire island of Ireland in the 1880s. If he hadn’t been so obsessed with maximal British sovereignty in Ireland, the island would probably not have been partitioned three decades later.

This argument will cut no ice with the Democratic Unionist Party, in whose hands the balance of Parliamentary power lies at a crucial moment. Their unbending insistence on Northern Ireland being treated exactly like the rest of the United Kingdom is ironic given that the existence of their party, and virtually all of their policies, stand as testament to the region’s distinctiveness.

That does not mean that the triggering of a backstop which treats Northern Ireland differently to the rest of the United Kingdom is a desirable outcome. That ambiguous place needs to be simultaneously connected to both the rest of the United Kingdom and the rest of Ireland, which would mean Britain having a closer relationship to the European Union after Brexit than envisaged in the Spectator’s original Leave-supporting editorial. Meaning membership of the Customs Union, and as much of the Single Market as can be negotiated.

You may ask: why should Ireland dictate Britain’s Brexit? The tempting answer is: why should Britain’s Brexit dictate life on the island of Ireland? But a better answer would be to point to the sovereign herself, who made the symbolic repairing of Britain’s relationship with Ireland one of the final diplomatic campaigns of her reign, most notably in her state visit in 2011. Central to this enterprise was acknowledging how ambiguous the relationship between the two islands has been. Nowhere more so than in Northern Ireland.

The sovereign herself thought that Britain’s relationship with the island of Ireland was important enough to take risks and make uncomfortable choices. Not all Brexit supporters will like it, but for the sake of Northern Ireland the best thing to do with the sovereignty being reclaimed from Brussels is very little indeed.

Matthew O'Toole was Number 10 Brexit spokesperson between 2015 and 2017