IT is a sign not of weakness, but of strength that there is at the moment so much impassioned debate in the nationalist movement about its way forward. Though the Scottish Government has, as usual, closed ranks, that has if anything inspired dissidents to raise their voices, from MPs such as Angus Brendan MacNeil to activists at the grassroots.

A consistent controversialist on that side has been the Rev Stuart Campbell, with his Wings over Scotland site the most-read blogger in the country. A nugget that emerged from his exchanges during this last weekend was that he might organise a Wings party to fight the Scottish election in 2021. He thinks Nicola Sturgeon is being far too cautious about the push for independence.

Since a lot of list votes go for nothing because the SNP picks up so many of the constituencies, a separate rallying point for the more radical electors could help to boost the majority for an early indyref2. There seems to be a fair degree of public support for something like this, to judge from Lord Ashcroft’s opinion poll last week and many other straws in the wind, not least the tireless writers of letters to the editor of The National.

They are all putting pressure on the chary First Minister to fire the starting gun for indyref2, whether the UK Government likes it or not.

A prudent politician, she was never going to stake everything on a single sample such as Ashcroft’s. In the past, she has said she would want to see a string of such results and preferably coming in at a level around 60-40% rather than last week’s 52-48%. Only then might she throw caution to the winds, so there is nothing surprising or inconsistent in her present hesitation.

And anyway, at Holyrood she has already responded to the radicals, though the fact appears to have passed them by. It was only in May that her government tabled the Referendums (Scotland) Bill which she wants to see enacted by the end of the year. The presiding officer certified that it fell within the Parliament’s powers. With support from both the SNP and the Greens, it seems certain to be passed.

When that happens, we will have a cast-iron legal procedure for going ahead with indyref2 in 2020, or at any other date in the future.

The Bill specifies that its referendum will be non-binding, but otherwise mimics indyref1 in 2014. That is the precedent in effect guaranteeing the legality of the procedure under the unwritten UK constitution. The instrument of this legality is a Section 30 order by which the Scottish and UK Governments agree the rules for a referendum. Is there any chance Boris Johnson would follow his forerunner, David Cameron, along that path? There is none at all but, by Halloween, Boris and his merry men could be out on their ears.

So let us turn from political speculation back to the likely legal position. All-party agreement to the referendum rules is vital, and cannot be won in Scotland alone. But this condition would have been fulfilled if the House of Commons passes the same Referendum Bill, or something very like it, as will be passed at Holyrood. Even the Tories and LibDems, the most vehemently opposed to the idea, would surely accept the validity of a statute approved at Westminster – or if not, they no longer accept even the existing UK constitution, let alone any attempts at modernising it.

One risk to the new statutory legal procedure is that Unionist parties will simply boycott a referendum held under its terms.

A Tory party being run by cavemen will certainly be tempted by that option, the LibDems scarcely less so, and even the Labour party might, at last, be able to make its mind up on something.

Referendums are relatively new to the UK constitution, but they are proving politically productive.

A Unionist boycott would be a further sign of that.

Boycott by the side that fears losing is already familiar in the politics of Catalonia. In its referendum of November 2014, 80% of voters were in favour of independence, but unfortunately, these amounted to just about 40% of the whole electorate. This would normally have been enough to win but, by staying at home, Spanish Unionists negated the apparent victory of the nationalists. They also gave the government in Madrid the excuse it needed, after Catalonia went ahead and declared its independence in November 2017, for a violent takeover and imposition of direct rule from Madrid.

If I were a Catalan, I would have been tempted to support the nationalist leader, Carles Puigdemont, who is like me also a journalist and a free-marketeer. But it must be said, now he is in Belgian exile, that he has left his political movement in a worse state than if he had not tried to force the pace.

Several of his closest colleagues are like him on the run and cannot return to their own country. Their cause languishes so long as the Spanish government maintains its tough stance, which it shows no sign of watering down. Catalonia is in effect under occupation.

And all this arose out of the Unionist boycott. Puigdemont was foolish not to think the consequences through. Equally, Scottish nationalists should ponder long and hard before they embark on anything like the same course.

Nicola’s reluctance may be vexing, but she does show a way forward which, even if taking longer to traverse, will at least avoid all the pitfalls that could bring ruin on the whole endeavour. That is something that needs to be thought about by those inclined to follow the Revd Stuart Campbell.

Catalonia also shows us a second danger to the cause of Scottish independence. One of the reasons the Catalan leaders are scattered to the four winds is that they found no sympathy whatever among other European governments. Spain is a full member of the EU and entitled to call for support from the remaining 26 members.

In recent times they have sought to cultivate solidarity in the politics of their external relations, just as they practise it in the economics of their external relations. Brexit is a good example of them doing both at once so that the UK attempts to find chinks in their common front have been wholly fruitless.

The EU took a tough line on the referendum in Catalonia. Donald Tusk, president of the European Council, called it illegal and defended the repression by the Spanish government. He and his colleagues in Brussels would deal only with the people in Madrid and ignored those in charge in Barcelona.

In other words, the EU is not generally in favour of rearranging the historical boundaries of the member states. It seems that, if such things are to happen, they must at least follow strict rules of constitutional legitimacy. Even then, a new nation may need to leave the EU and seek readmission, though this principle has yet to be confirmed by a real case. Spain itself is somewhat more permissive. Its present government says that if Scotland legally secedes from the UK, it will have no objection to the newly sovereign state rejoining the EU as a full member.

There is altogether a great weight of evidence that Scottish independence will come only by following the legal, constitutional route through agreement with the UK and not in defiance of it. Unionist boycott and international recognition are serious issues, and this is the only way of dealing with them. The route may be longer and drearier, but it will lead more surely to the destination. Nicola Sturgeon is right, and the Rev Stuart Campbell is wrong.