IT’S always a pleasure to bob and weave with Ian Johnstone of Peterhead, one of my regular sparring partners. We differ about many things, though there are occasional points of agreement which are all the more gratifying to me. There is no obvious one at the moment, however.

In response to my column last week which doubted the wisdom of a snap indyref2, Ian wrote in to make this point: “Scotland remains an equal partner of a Union that was formed as a partnership of equals. It is puzzling where Mr Fry finds legitimacy for his notion of Westminster holding veto power over Scottish independence. Perhaps he might explain this to those of us who could well qualify for his description as ‘gung-ho, hell-for-leather’ independence seekers?”

As a matter of fact, I did not rest my case on the Treaty of Union.

It is still in force after 300 years, but I do not doubt for a moment that the Scots people are entitled to dissolve the Union by a vote in a referendum.

In fact, I would admit the validity of other means to the same end.

It used to be the official position of the SNP that winning a majority of Scotland’s MPs at Westminster would be enough to do the job, which if followed through could have brought independence in 2015.

But since the re-establishment of the Scottish Parliament, this position has been abandoned. We now have better, if not always simpler, means of giving expression to the popular will.

The treaty showed, as Ian said, an “earnest solemnity and far-reaching intention”. It has all the same often been breached, usually by the UK Government but occasionally because Scots preferred it to be breached for some greater purpose, like extending the electoral franchise. Yet it has succeeded in its most essential purpose of preserving Scottish civil society in a Union bound to be dominated by a much bigger and more powerful neighbour.

If it had failed in that task, I don’t think we would today be talking about the independence of Scotland any more than we talk about the independence of Lancashire.

No, I rested my case specifically on the Edinburgh Agreement between then-First Minister, Alex Salmond, and then-Prime Minister, David Cameron, which dealt purely with the mechanics of holding indyref1 in 2014 – a matter of process not principle.

It entailed the invoking of Section 30 of the Scotland Act 1998, so as to hand over to Holyrood the necessary powers for running a referendum. In her wisdom, the present First Minister has indicated that she wants to follow the same procedure for indyref2. Already, the present Prime Minister has rejected the very idea of indyref2 and will no doubt do the same so long as she remains in office. This, though, is unlikely to be long.

Therefore, section 30 remains a live option. It can stand as the definitive procedure for altering Scotland’s constitutional status and if necessary, might be used over and over again. I don’t think it is worth rehearsing here the various circumstances in which it might conceivably be invoked because in a fluid political situation, they change all the time. But, it would offer the advantage of precedent, of having worked before to the satisfaction of all parties involved – or at least with their acquiescence. And the English adore precedent. It is the basis of their entire constitution and indeed, the only thing they can rely upon in the absence of the single written document that sensible countries draw up for themselves. Altogether, then, we have a constitutional way out of the Union, as Nicola Sturgeon sees. One of these days, we will be able to take it.

I don’t think the alternative route of challenge and defiance offers nearly the same chance of success. And I fear a downside risk that could bury the project of independence for good. Last week, I dealt with some of the mechanics of getting a unilateral statute for holding a referendum through the Scottish Parliament, so I’ll leave those difficulties aside now except for making two points.

They would crystallise Unionist arguments on the unconstitutional nature of the whole business in circumstances where public opinion was still split about half-and-half (at best). And, they could well provoke the Tories, Labour and LibDems –who would have opposed the statute in the debates at Holyrood – into boycotting the subsequent referendum. A referendum where only 50% or so of the electorate votes is, as Catalonia found out in 2017, almost worse than no referendum at all. In fact it may discredit the referendum as an instrument of constitutional change for Scotland. What then?

In contrast, a referendum under Section 30 would, by definition, be one where all participants – Yes and No; government and opposition; nationalists and unionists – would have bound themselves in advance to accept the majority verdict of the Scots people. Democracy in action – indisputable and unimpeachable in law.

There is a further stage to the argument. Suppose Scotland does win independence after Brexit, along one route or the other, and then wants to rejoin the EU. Before indyref1, we were warned Brussels had no interest in legitimising secessionist states. José Manuel Barroso, president of the EU commission, told Scotland it might be tough, but that’s how things were going to be. His warnings came true in a different way, in the brutal rejection of Catalonia’s claims by all the European institutions.

Spain is reckoned to have been behind the rigidity. Like the UK, it threatens to break apart. It will not tolerate any EU indulgence to separatist movements, and as a big member state it can get its way – or so we are told.

As a matter of fact Spain’s position is more sophisticated than that. The Foreign Minister in 2017, Alfonso Dastis, knows something about Scotland because he likes to play golf at Gleneagles and he softened the line. So long as the UK had satisfied its own constitutional procedures in agreeing to our national independence, he was not going to be “more Catholic than the Pope”. The written Spanish constitution forbids secession, while the unwritten UK constitution does not. That was good enough for him. His successor in a new government in Madrid, Josep Borrell, has confirmed this as the official line. In neither case does it lessen their opposition to the secession of Catalonia.

These two men to me seem to present another clinching argument for a Scottish referendum going by Section 30 rather than following the Catalan do-it-yourself model. If we win independence under the first procedure, we will be back in the EU no bother at all and if we do so under the second procedure Spain will veto us.

All of this reinforces the case I made last week for not expecting the referendum before 2023/4. We can use the interval to effect by wooing still dubious groups of the Scottish population so that the win will be all the more convincing in the end. This vehicle must be built for safety, not for speed.