Alex Massie is a columnist for the Times (London).

Boris Johnson is prime minister of what is still, for now, the United Kingdom of Great Britain and Northern Ireland — and he would very much like to keep it that way. Mindful of his own place in history, he has no intention of agreeing to a new referendum on Scottish independence that would risk, even invite, the break-up of Britain.

No wonder he announced this week that he refused to countenance such a vote. By doing so, he bought his government time. But this is a battle postponed, not a battle won. The question of Scotland — and, with it, the question of the United Kingdom itself — has neither been answered nor gone away.

Johnson may be master of all he surveys at Westminster, but his writ does not extend to the whole of the United Kingdom. The fire lit in 2011, when the pro-independence Scottish National Party won a majority of seats in Scotland’s devolved parliament, still rages. In December’s general election, Scotland remained immune to Toryism. The SNP won 48 of Scotland’s 59 constituencies, the Conservatives just six.

The immediate cause of this fresh rupture between England and Scotland is Brexit. Johnson was elected on the back of a promise to “Get Brexit Done.” That will be accomplished at the end of this month. Three-and-a-half years after the Brexit referendum, Brexit is finally happening. But at what price?

At its simplest, without Brexit there would be little debate over Scotland’s place at the heart of the U.K. In 2014, Scots voted — 55 percent to 45 percent — in favor of maintaining a parliamentary union first established in 1707.

And there the matter might have rested for a generation — if Brexit hadn’t come along. England (and Wales) voted to leave the European Union in the 2016 Brexit referendum, but 62 percent of Scottish voters opted to remain. At a stroke, the conditions for the “meaningful change in circumstance” Nicola Sturgeon, the leader of the SNP and Scotland’s first minister, deemed necessary for reopening the independence box were met. Scotland, she insists, must have the right to choose its own destiny.

Most opinion polls suggest the question is much too close to call. The most recent, published just before the December general election, reported support for independence at 49 percent.

Hence Johnson’s abrupt dismissal this week of the Scottish government’s request for the legal right to hold another referendum. In 2014, Tory ministers note, senior SNP figures suggested that a referendum was a “once in a generation” opportunity to choose an independent future. Now Tory politicians are busy reinterpreting a “generation” as anything from 30 to 50 years or even, in one case, to the rest of Sturgeon’slifetime.” (She is 49.)

That line will hold for now, not least since there is no majority enthusiasm for another referendum before the shape, meaning and implications of Brexit have become clear. The relationship forged between London and Brussels necessarily informs that between Edinburgh and London. As a practical matter, the possibility of a “hard” border between an independent Scotland and the rump-U.K. complicates the prospects for independence.

As a matter of economic self-interest, independence might prove an expensive business for Scotland. But as Brexit has demonstrated, economic self-interest isn’t always the most important thing in voters’ minds. If Union remains something of measurable financial value to the nation in the north — Scotland spends roughly $16 billion more each year than it raises in taxes — psychologically it often feels semi-detached from the United Kingdom of which it is part.

The sense of a Scotland powerless to control its own destiny is the SNP’s most powerful argument. Just as Brexit was advertised as a means by which Britain could “Take back control,” so independence is imagined as a comparable exercise in national self-determination and self-realization.

The tide is with the nationalists, too. Opinion polls routinely suggest most Scots believe independence will happen one day and that Brexit is making at least some rethink their constitutional preferences. Support for independence is also notably higher among younger Scots than their elder compatriots.

The nationalists, secure in their northern fastness, have become Scotland’s “natural” party of government. Elections to the Scottish parliament next year may produce a pro-independence majority armed with the moral artillery required to force the issue once again. Unionism may say “No” for now, but that is not a long-term strategy for survival.

Contained within that adamant refusal to even consider the question, however, is a deeper, lurking, truth: The apprehension that if there were another referendum the nationalists might win it. If so, that would make Boris Johnson the last prime minister of the United Kingdom. A guarantee of a place in posterity’s almanac, perhaps, but not a happy one.

Johnson’s victory last month, then, may yet contain the seeds of his country’s downfall. Brexit must be achieved at any price — even the dismantling of the country it was notionally supposed to liberate.

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