Last week, Labour’s shadow Scottish secretary, Ian Murray, suggested that three should be a fixed set of rules to determine constitutional referenda. His comments add to to a growing body of opinion that the UK needs a mechanism governing how its four constituent countries could secede from it. This is bound to raise hackles among some unionists  – The Times headline covering Murray’s proposal was “Labour’s referendum plan could open way to independence vote” – but in truth it addresses a genie that escaped its bottle long ago.

Scottish Nationalists are forever telling us that they have a democratic ‘mandate’ for another referendum on independence. They base this in part on the fact that they won a majority of seats at the last Holyrood election, but their claim also lies in precedent that the UK government itself set. In agreeing to the 2014 referendum, the UK conceded that its constituent nations have the right to secede if the democratic will is there. The only question, then, is how that will is interpreted, and by whom – by nationalists, by a UK government, or by a neutral set of rules that gauge the views of the people clearly and decisively.

The constitutional contest is currently skewed heavily in favour of nationalists, particularly in Scotland. There is an election of one kind or another most years and each one is capable of being treated as another referendum by proxy by those who seek to do so. They only have to be lucky once.

So far, the SNP clearly does not have a mandate from these elections. The irony of Brexit is that, despite its unpopularity north of the border, it caused a drop in nationalist support because it re-focussed voters’ minds on the greater threat of independence.

In the two elections before the Brexit referendum, nationalists averaged 49% of the vote and in the four since that referendum just 41%. The latter figure includes the 46% they scored at the general election in December, at a time when, with Brexit and Boris Johnson to the fore, they would have hoped to do even better.

Winning a majority of seats doesn’t count when it comes to independence – you need a majority of votes. But these serial losses don’t particularly worry the SNP. Their relentless pressure has forced some unionists to concede that if they win the next election – for the Scottish Parliament next May – that gives them the right to hold another referendum, presumably on their terms again.

The constitutional contest is currently skewed heavily in favour of nationalists

So all it takes is a blip in the polls, a minor crisis at UK level (let alone a pandemic) or a good month for Sturgeon, and the UK is in the balance once again. It’s Russian roulette with only one side pulling the trigger.

This endless constitutional drama is damaging in lots of ways. Scotland suffers from a kind of permanent Brexit crisis magnified by ten. It causes uncertainty for business and individuals and skews politics away from crucial issues like education, health and the economy which have lacked meaningful attention in Scotland for years.

What is more, such pressure does not allow voters’ intentions to be assessed properly. So Ian Murray has a point. But how would a set of rules work that recognised the democratic right to secede while ensuring a clear and decisive result?

Here are five suggestions:

1. If secessionist parties won a majority of votes and seats at a devolved election (or, for English secession, at a general election) in which they had clearly stated their desire to leave the UK, they would have the right to trigger a vote.
2. To ensure a decisive outcome and guard against constant constitutional crisis, such votes should only be held “once in a generation” – as the SNP itself accepted last time. No subsequent vote could take place for at least the three subsequent parliaments (so 2030 at the earliest), which means there would be at least sixteen years in which normal politics could resume.
3. The rules of any referendum would be set in advance so that nationalists could not attempt to fix the result by setting the wording of the question, the timing of the vote or the franchise. A balanced question along the lines of that used in the EU referendum should be used.
4. The result of the vote would have to be decisive, reflecting the clear will of the people. 50% of the electorate should have to back secession, rather than 50% of those who vote. Such an important matter should not be decided on a minority of opinion. In the 2014 referendum, turnout was 85%. A 51% vote for independence would only have accounted for 43% of the electorate, which is not a clear mandate for such a momentous decision. Instead, under this rule, the nationalists would need 59% of the vote to win on the same turnout – a decisive margin which would be a clear basis for independence.
5. But in the event that secession won more than 50% of the vote but less than 50% of the electorate, the result would be unclear. In this case, secession would be provisional, subject to a confirmatory vote after a two year period of reflection in which the nationalists could prepare for secession and negotiate terms with the UK government and others. In this period some of the political and economic consequences of independence would become apparent, allowing a more informed vote thereafter. The confirmatory vote would be based on a simple majority basis – 50% of the vote plus 1 would be enough to win. This “double lock” mechanism was in fact suggested by the SNP for resolving the debate that took place after the narrow Brexit result. Some argue that a confirmatory vote mechanism would give the UK government an incentive to make the negotiations as difficult as possible. But on the other hand it would force the debate during the original vote to be realistic, with the public informed properly about the risks.

This arrangement offers something for everyone. Nationalists would have enshrined the right to secede. Society at large is saved constant uncertainly. The electorate is presented with clear choices at elections: They know whether the consequences for voting nationalist would result in a referendum or not.

Finally, if a new vote did take place, it would result in a truly decisive decision that could be accepted by all.