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The former Conservative prime minister, Sir John Major, warned that a vote to leave the E.U. endangered the United Kingdom. He recently repeated this warning as it has become clear that the tone of Mrs. May’s government has become harsher and more strident. The harder the Brexit, the cleaner and more complete the break with the E.U., the more likely the disintegration of the U.K.

Last week’s Assembly elections in Northern Ireland make the point. There was a shift, a small shift, away from unionism. Sinn Fein, which seeks a united Ireland, gained ground. The laboriously confected peace process is being slowly undermined. The question of the border with the Republic is alive again. If Brexit results in a hard border, with customs posts and passport inspection between North and South, a return of the Troubles is all too possible. If, on the other hand, the border remains as open as it is now, then it will be difficult to prevent the Republic from becoming a gateway for immigrants from E.U. states to the U.K. Either way, the future is murky, and with the Catholic Church’s loss of power and influence in the Republic, one obstacle to a united Ireland has been removed.

Paradoxically, keeping the border between North and South soft and open might benefit the nationalist cause in Scotland. One of the strongest arguments against independence is the existence of a single market with England. But if a soft border with the Republic keeps Northern Ireland in the U.K., then it will be argued that a precedent for an open border between an E.U. state and the U.K., or, let us say, England, has been established. So why not with an independent Scotland, even an independent Scotland that has been accepted as an E.U. member state?

The U.K. as at present constituted is not doomed. There is still life in the old girl. But Scotland’s commitment to the union is weaker than it was, and I think that commitment is draining away. I don”€™t like this. I”€™ve always been both British and Scottish. But the strident English nationalism of the Brexiteers is eating away at Britishness. Unless there’s a change of tone I fear it will wither away. Sadly, I don”€™t think the English much care. Someone once said that the British Empire had been created in a fit of absence of mind; it seems that the U.K. is disintegrating in like manner.