PRIME Minister Theresa May is right to dismiss talk of another independence referendum. She should stick to her guns. I admit to being puzzled that Ruth Davidson, leader of the Scottish Conservatives, does not also support her. The notion that another referendum is solely a matter for Scotland to decide is wrong.

Secession is one of the toughest of state problems; the world is scarred by examples where it has gone wrong. Two years ago Britain, one of the world’s great liberal democracies, showed the debate could be carried out peacefully with credit due to the SNP for its part in the democratic process.

After 30 months of debate, independence was rejected by a margin of 11 per cent in a referendum in which 85 per cent of those eligible voted. This was the world’s longest referendum campaign held on a date chosen by the SNP to rules approved by the Scottish Parliament.

With the resources of the Scottish Government to hand and led by the most charismatic of Scottish politicians, independence gained a tranche of new enthusiastic support but no great new consensus. It is hard to see how the result could have been more legitimate.

Nobody thought this result would stand for ever but both sides accepted it was for a generation. Barely two years on, the First Minister is threatening the Prime Minister with another referendum.

But there is a difficulty. Nicola Sturgeon wants public opinion to have moved substantially in favour of independence before she “demands” the second and final independence referendum. While she hasn’t put a figure on it, several senior colleagues have briefed that it should be “60 per cent for a year”.

This is not just a matter of getting a safe margin when polls have become so unreliable. After the oil shock, Ms Sturgeon understands that a nation lacking consensus does not easily make a new state.

Comparing the 44 per cent backing independence in 2014 with the consensus backing the Scottish Parliament in 1997 (75 per cent), the Good Friday agreement in 1998 (73 per cent) or routinely supporting independence in the referendums held around the world since 1945 (usually upwards of 70 per cent) shows just how far short she is. Beside these majorities, “60 per cent for a year” can at least be rated a start towards consensus.

Yet there seems to be no analysis from the SNP as to why independence failed to build a consensus or what new case will be offered. It can be little surprise that opinion hasn’t moved towards 60 per cent.

Brexit has created a new excuse for another referendum; it has not yet created a consensus for independence. The First Minister may well find that voters do not hold the parity of esteem between the two unions that she hopes they do. Maybe in one bound, she will be free; perhaps not. Time will tell.

Leadership means taking people where they want to go or, the harder part, convincing them to go elsewhere. She needs the courage to explain to her 60,000 new members that a few more points on the leader board do not qualify as a consensus.

The rest of Britain could not vote in the 2014 referendum yet watched as the UK was taken to the brink of a break-up. On behalf of the rest of the UK, Mrs May would be right to insist there is a consensus among Scots for such radical change, not only in the polls but also at the ballot box.

The practical way to do that is to abandon a simple majority vote in favour of a super-majority in any future referendum; for example, 55 per cent of those voting instead of 50 per cent. It is a feature of constitutional referendums elsewhere. Such a request will be politically hard to resist from those who have no vote but do have a legitimate interest in the future of Britain and the secession of Scotland.

If Ms Sturgeon demands a premature referendum, Mrs May should counter with the condition that there is a super-majority. If you believe this far-fetched, consider how the use of a referendum for a Scottish Parliament came like a bolt from the blue in 1997.

At present, a simple no from the Prime Minister is enough.

Nigel Smith chaired the cross-party Yes campaign in the 1997 referendum setting up the Scottish Parliament and is an expert on referendums.