The reasons behind these three initiatives are distinct, but related. In Dublin there is increasing apprehension about the call for a referendum on the border; in London there is increasing apprehension, shared by Conservatives and Labour alike, about the call for a referendum on Scottish independence. Given that they are all running on parallel tracks it is curious how each initiative fails to acknowledge the others. For instance, the Shared Island document has a section which lists the challenges to good relations in Ireland, and while no-one would deny that Brexit and climate change deserve their places on any list of challenges the fact remains that there is nothing so likely to disrupt relations in these islands as Scotland voting for independence, a consideration which doesn’t earn a mention in the document. But if that domino falls, we can expect its nearest neighbour to feel the impact.

How likely is that to happen? We will know very soon. The May 2021 election will be taken as a proxy for a vote on independence, a ‘referendum on whether there will be a referendum’. The latest Ipos MORI poll, conducted on 20–26 November predicts that the SNP will take 55% of the seats, consolidating its dominance of Scotttish politics. Once it gets its parliamentary mandate it will throw down a challenge to the Johnson government by calling for the second independence referendum. This wasn’t supposed to happen. The 2014 referendum, in which the union side defeated the independence side by 55% to 45% was supposed to settle the issue ‘for a generation’. Clearly something has changed. The last 17 major polls have shown a majority of Scots support breaking the link with England, with a settled percentage of around 55% – thereby reversing the referendum result almost exactly. The word ‘inevitable’ is now cropping up with increasing frequency in articles about Scottish independence. While it would be wise to heed the warning by AJP Taylor that, ‘Nothing is inevitable until it happens’ the general expectation is that within the next year the Scottish parliament will precipitate a constitutional crisis by demanding a referendum. Boris Johnson has made it clear he will deny the request, but when he does he will be pouring petrol on the flames his Union Unit was supposed to douse.

Those concerned about a border poll in Ireland should pay heed, because the dynamic behind developments in Scotland is also taking shape in Ireland. The increase in support for Scottish independence is sometimes wrongly characterised as resulting from an increase in Scottish nationalist sentiment, but that is to misunderstand what is influencing those now prepared to break up the UK. Professor John Curtice, the doyen of pollsters, ascribes the change to three things: Brexit, Covid and Johnson. This is not a rebellion by haggis eaters. The crucial constituency, the one that is tilting the balance, is made up of people who voted to retain the UK link in the last referendum but who now, with varying degrees of reluctance, are coming to see independence as the lesser of two evils. Writing in the New Statesman, Colin Kydd described them as ‘double unionists’, and estimates that they make up about 30% of the electorate. These are people who didn’t want to be trapped within a narrow Scottish nationalism, so they voted to remain in the UK. Equally, they didn’t want to be trapped in a narrow British nationalism and so they voted to remain in the EU.

When that option was crushed by the Brexit vote a slow re-orientation began, one that sees the hope of living in a modern social democratic state having more chance of being realised in an independent Scotland than in a UK structure dominated by a surging English nationalism. At the start of 2020 the two sides in the independence debate were equally balanced in the polls: Brexit had still not given the independence side the upper hand. The first poll to show that happening came in May after Covid had begun to affect the body politic. It was the competence of Nichola Sturgeon, paired with the incompetence of the Johnson administration, that served to convince a section of the ‘double unionists’ that they should break the link. The personality of Johnson is not irrelevant to this development. It is hard to overstate how much he is disliked, indeed loathed, in Scotland. A poll in October by JL Partners, the firm led by Theresa May’s former pollster James Johnson, found antipathy towards the Prime Minister to be the most important factor in swaying swing voters. The seal was then set on this relationship with the leaking of comments made by Johnson on a Zoom call, that Scottish devolution was ‘Tony Blair’s biggest mistake’. The spin doctors couldn’t spin him out of that one.

But how might John Curtice’s three factors – Brexit, Covid and Boris Johnson – play out in Northern Ireland? The shape of the Brexit arrangement has left Northern Ireland on the window ledge of the union, partly in the UK but also partly in the customs union of the EU (future historians of unionism will scratch their heads trying to understand why the DUP acted as cheerleaders for Brexit). The NI Assembly, despite a good start, has mismanaged the Covid crisis dreadfully. Disastrous quarrels over lockdown have raised fundamental questions about whether power- sharing can ever be workable. The hinge constituency here, the one equivalent to the ‘double unionists’ in Scotland, is that of middle-class Catholics. These are people who voted to stay in the UK as part of the Good Friday Agreement. They then voted to stay in the EU. Frustrated in that second hope, and totally alienated by the Johnson administration, they are likely to reach a tipping point if Scotland votes for independence.

In short, the three ingredients that have brought Scotland to the point of a constitutional crisis are also bubbling away in Northern Ireland. It may therefore be worth mentioning one more new unit. Peter Robinson is calling for a special Northern Ireland think tank to help ensure the link with the union is maintained. If he manages to get it off the ground it will have its work cut out for it.