The writer is a former director-general of devolution at the UK Ministry of Justice

Divining the will of the people from an election result resembles the ancient Roman inspecting the entrails of slaughtered animals. It’s easy to see what suits you politically. After the Scottish election, Nicola Sturgeon sees that, since a majority of MSPs again support another independence referendum, it is the will of the people. She has a mandate, and Boris Johnson must give her the legal powers.

Those entrails actually divide neatly into halves. Half of Scotland voted SNP, half didn’t. Poll them, and only half want another referendum within five years. Sturgeon’s politics are obvious. Promise what she has no legal power to deliver, demand and be denied that power. Best of all, make Johnson stop an illegal referendum in court. Many may resent that, so up goes her support.

The prime minister is not obliged to keep Sturgeon’s promises for her, but the ball is in his court. A flat no plays into her hands. Some suggest calling her bluff with an early referendum, but he cannot simply hand control over the UK’s future to those campaigning to end it. He can say neither yes nor no. The solution to his dilemma is one he may find unpalatable.

It begins not by arguing fruitlessly about precise results, legalities and mandates, but with the underlying constitutional and political reality. The UK is a multinational union of consent, which in the end the Scottish people could choose to leave, and there is undeniable dissatisfaction in Scotland.

As UK prime minister, responsible for the whole union, he can neither ignore that dissatisfaction, nor give the SNP carte blanche to exploit it. His duty to the people of Scotland and the rest of the union is to promote a measured, orderly and stable resolution of the question. Scotland cannot sustain more constitutional uncertainty, nor should the rest of the UK be obliged to endure it.

Here comes the unpalatable bit. To save the union, Johnson cannot be simply an English — by courtesy, British — nationalist competing with Scottish nationalists for the allegiance of Scots. He can only lose that competition. Instead he has to take responsibility for helping the Scottish people make up their collective mind on a stable, long-term relationship with the rest of the UK.

This may be easier than it sounds: there isn’t going to be another referendum any time soon — as even Sturgeon says — so there’s time to explore all possibilities thoroughly. Look in depth, objectively and independently, at what independence would actually mean — for the pound, the border with England, the very difficult fiscal situation and so on. Despite decades of debate, there remains a hunger in Scotland for facts about independence.

But look too at the other options. Not just more devolution — the Scottish parliament is already powerful — but how to fix the real problems in relationships, representation and voice at the centre of the UK. Johnson has a potential trump card: those are not just devolved nations’ problems. As decentralised power accelerates within England, he is meeting the same demands from Metro mayors and others — some his political allies. He can make improvements now, but a principled review of the UK territorial constitution is inevitable.

Johnson can argue a referendum might possibly come at the end of that, not kick it off. It could still mean independence, but a substantial majority of Scots might endorse a reformed relationship. Even if half might vote yes today, about two-thirds still feel at least partly British, and three-quarters want Britain’s governments to co-operate more.

Johnson must change from buccaneering Brexit nationalist to measured constitutional statesman. Minister for the union, not just unionists. A big ask, maybe, but otherwise the next entrails examined will be of the career of the man who did not take back but lost control of Britain.