What does a hard Brexit mean for the unity of the United Kingdom?

Nationalisms disrupt multinational unions, and not just European unions. Brexit is a nationalism that matters not just for devolved powers in the UK, but for the stability of the union too. It is English but not UK nationalism, and so in Scotland and Northern Ireland its challenges are existential. The Scottish National Party are now at Refcon 1, with Nicola Sturgeon edging daily closer to calling a second referendum on independence. Northern Ireland’s administration collapsed for its own reasons, but Brexit and its consequences make building a new government much harder.

Nowhere is the issue clearer than in Scotland. Though the SNP lost, the 2014 referendum still established the party as the overwhelming force in Scottish politics. After 10 years in office, and with all but three of Scotland's MPs, SNP politicians are used to dominating the political agenda and have been preparing for the next shot at independence whenever they and public opinion are ready. So Brexit was an unwelcome shock. Not only has the SNP been a pro-European party for over 20 years (the European Union provided a useful safety net for independence) but Brexit has put Scotland's relationship with England back on the agenda today, not at the time of the party’s choosing.

This is perhaps why Nicola Sturgeon was initially flustered. In the 2014 referendum, guaranteed EU membership was part of the case for Scotland staying in the UK. And now only 38 per cent of Scots voted Leave, compared to 53 per cent in England. So her immediate reaction was that a referendum was "highly likely." But then she seemed to vacillate. If the UK—or even just Scotland—remained in the single market, Indyref2 could be avoided. This was a twin-track approach: always aiming for independence, but prepared to defer another referendum if she could make headway with the UK government.

Little progress emerged from the discussions between the governments. For six months Westminster had nothing to say, and then Prime Minister Theresa May announced she wanted the UK out of the single market and the customs union too. This looked like a fait accompli to the devolved administrations: all were pro-single market, and Northern Ireland pro-customs union. The Scottish government’s single-market-for-Scotland-only plan is still formally on the table (although few seem to regard it as plausible) and there are big issues to work out on repatriation of devolved powers, such as agriculture. But it’s hard to argue that the views of the Scottish and Northern Irish have had much impact on UK decisions so far.

Sturgeon’s emphasis has changed recently: compromise, she says, is what the UK is rejecting. Her rhetoric has changed, shifting its focus from Europe to England and how it is Eurosceptic, austerity-loving, Trump-friendly, and above all Tory—and thus how different from Scotland. One senses Sturgeon’s backseat driver, Alex Salmond, would have launched a campaign six months ago. He predicts a vote in autumn 2018 and Sturgeon is moving towards his position. Committed Yes campaigners are gearing up for the next campaign, taking lessons from Brexiteers’ post-truth success.

For the SNP it was always about independence, but Sturgeon has not been insincere, as her offers of compromises all have independence in view. If the UK was to stay in the single market, independence would be easier in the long run—there would be no hard border between Scotland and England, for example. Or, Scotland being in the single market while still in the UK would look a lot like independence over much economic policy. If one of these is now ruled out by the prime minister, and the other seems implausible, the SNP is now “forced,” apparently, to go for a referendum now.

But it’s not as simple as that. Scottish public opinion has not moved in line with nationalist outrage. Only core nationalist supporters want another early referendum. Independence voting intentions are roughly the same as in 2014. For every liberal Europhile who has moved towards independence, a Eurosceptic nationalist has moved the other way. Would the 400,000 independence supporters who were also Leave voters turn out to throw off one foreign yoke just to retain another?

Hence Sturgeon’s recent change from Europe’s virtues to England’s vices. Second, although Brexit makes the emotional case for separation easier, the objective case has got much harder. With oil revenues at zero, Scotland’s fiscal position has moved from deeply parlous to catastrophic. Brexit undercuts the SNP’s currency plan: how could Scotland, putatively an EU member, share a currency with the UK? An SNP “growth” commission has been tasked with finding a new economic plan, but has produced nothing yet.

Economically, the UK matters much more to Scotland than the EU. EU membership would mean safeguarding Scotland’s EU trade at the price of UK trade, which is four times bigger. A customs border at Carlisle means Hadrian’s wall would once again mark the edge of Europe. As Scotland will leave the EU along with the UK, most likely in March 2019, it even risks being in neither union for an uncertain period.

Finally, holding a referendum is not Sturgeon's call. The Scottish Parliament had to be given special, one-off, legislative competence in 2014. Westminster would need to do the same again, in a so-called section 30 order. That card is in May’s hand: she can exercise a veto not only on whether there is a referendum but on what question is asked and when. So far she says simply that there is no case for one.

Leaving the EU is as at least as destabilising for Irish devolution as Scottish. Northern Ireland voted to remain, but divided on traditional lines, with Republicans more likely to support remain. Brexit did not cause the collapse of the Northern Ireland Executive—that was down to several years of increasing mistrust between the Democratic Unionist party and Sinn Fein, capped by a financial scandal of spectacular size and incompetence. But it did not help, and will make rebuilding government much more difficult. The landscape has changed. Common EU membership underpinned the Good Friday agreement, and took the border out of Irish politics. It’s back in now.

No one in Ireland knows what to do about Brexit. The economic effects on the Republic could be profound. Given the pattern of its trade, Ireland looks like getting all the downsides of Brexit without any of the putative upsides. The Irish government is coming to terms not merely with the UK leaving the EU, but insisting on a customs border within the island of Ireland. So the fractal line badly drawn round six Protestant counties in 1923 becomes not just the external border of the EU, but a customs barrier too, and one crossed by literally hundreds of roads and tracks.

Both governments talk about making it as frictionless and invisible as possible, but some physical border checks look inevitable. The economic effects, on cross border supply chains for example, will be tangible, but the political consequences more significant. Initial demands for a Border Poll on reuniting Ireland have subsided, but might recur. Add the now deeper constitutional divide to the poisoned DUP-Sinn Fein relationship, and forming a new Belfast administration looks next to impossible, with unpredictable effects on the stability of Northern Irish politics. The prime minister might not relish dealing with the devolved Scottish government, but imposing direct rule and becoming the devolved Northern Irish government isn't an attractive prospect either.

Theresa May entered office as a tepid Remainer who now accepted the referendum result. After all a long period of indecision, her approach to leaving the EU puts her firmly in the centre of the Leave camp. As a former Home Secretary, she prioritises immigration control. As a Conservative leader, she targets the median Conservative voter, not median UK opinion. As a result, consciously or not, she behaves like an English nationalist, and the terms on which she proposes to leave the EU have, so far, paid little more than lip service to the devolved interests of Scotland and Northern Ireland in particular.

But there remains a great deal to play for. Perhaps May—said to be the kind of politician who likes to deal with one problem at a time—will now turn more of her attention to keeping the UK together as it leaves the EU. She has cards to play, such as control over whether there is any Scottish referendum, and its terms. She may have the imagination to devise, with Dublin, a new border solution. And more important, she will have the scope to be both imaginative and generous in how power is distributed across this new United Kingdom, giving the devolved bodies more space to express priorities which differ from England's, perhaps even over some EU relations. To lead a union, she will have to balance the different nationalisms within it. Otherwise she risks becoming the Prime Minister not of the UK, but of the Kingdom of England and Wales.