THE legal obstacles to a second independence referendum are formidable but not insurmountable – so I argued in these pages last week. If there is to be a Bill for a second independence referendum (still the wait goes on…) and if, as everyone assumes, the lawfulness of that Bill is challenged by UK ministers in the Supreme Court, what would the Scottish Government have to argue in order for their Bill to be upheld as valid?

Scottish Ministers will have two main arguments at their disposal. Holyrood legislation is unlawful if it “relates to” a matter reserved to Westminster. Whether legislation relates to reserved matters is to be determined by reference to the “purpose” of that legislation, having regard to its “effect in all the circumstances”. So says the Scotland Act.

The Union is reserved. Therefore, in order to win in the Supreme Court, the Scottish Government would need to persuade the judges that any legislation paving the way for an independence referendum did not “relate to” the Union. This they would have to do by making submissions to the Court about the legislation’s purpose and about its effect.

The purpose of the legislation, Scottish Ministers could argue, is to consult the people of Scotland. There is nothing in the Scotland Act to prevent or forbid Holyrood from doing that and, indeed, in 2020 the Scottish Parliament passed the Referendums (Scotland) Act, which sets out a number of general rules and procedures by which referendums may be conducted in Scotland. As far as I am aware, no-one has challenged the lawfulness of that legislation in court.

If the legal purpose of any Independence Referendum Bill is to terminate the Union, it will be unlawful. But if its legal purpose is much less ambitious than that, and is confined to asking the Scottish people for their opinion about independence, there is nothing in the Scotland Act to suggest that may not be done.

However, this would be to do as if a referendum were nothing more than a glorified opinion poll. In law, perhaps that is all a referendum is. But, in the real world, we all know that is a nonsense. Nobody regarded either the 2014 independence referendum or the 2016 EU referendum as invitations merely to express opinions. Rather, they were formal decision-making devices in the which the electorate decided that Scotland should not be independent and, again, decided that the UK should leave the EU.

Showing, therefore, that the purpose of any IndyRef2 Bill was merely to consult people would be possible in theory but is rather more difficult in practice.

Difficult, but not impossible, especially when we think also about the “effect” of any future indyref. On this point, Supreme Court case law may help the Scottish Ministers’ case for, in 2017, the Court stated that the 2016 Brexit referendum had no legal effect: that referendum “did not change the law”, the Court ruled. This, said the Court, did not mean the referendum was “devoid of effect” but it did mean that “its force is political rather than legal”.

Withdrawal from the European Union was delivered not by the 2016 referendum, but by legislation passed by Parliament. Whilst such legislation would not have been enacted but for the 2016 referendum, strictly speaking, the legal effect of the referendum itself was nil.

This is why referendums are sometimes, albeit not very helpfully, described as advisory. It’s unhelpful because, even though legally correct, this language fails to capture what referendums are in practice. Whatever the legal niceties, referendums decide things.

The “effect” of any IndyRef2 Bill, on which the Supreme Court will have to rule, is, in the terms of the Scotland Act, its effect “in all the circumstances”. What is the narrow legal effect of an independence referendum? Likely, nil (in which case it does not relate to a reserved matter and could therefore be lawful). But what is the effect “in all the circumstances” of an independence referendum? Monumental. A Yes vote will mean the break-up of Britain and the creation of a new Scottish state in international law. Given “all the circumstances” the effect of any IndyRef2 Bill could be huge (and, because those effects relate to reserved matters, unlawful).

All this dancing on legal pinheads may seem dizzying, but it boils down to this. Absent Westminster’s consent, which is sure to be withheld, Holyrood legislation paving the way for a repeat referendum on independence will be lawful only if the Scottish Ministers are prepared to concede (1) that its purpose is merely to consult the people rather than to make any decision about independence and (2) that its effect is zero—i.e. that no legal or constitutional consequences would attach to any Yes vote. It would just be an opinion poll, like any other opinion poll.

It follows, of course, that such a referendum could safely be ignored, just as opinion polls routinely are. Those opposed to independence or, indeed, those opposed to another independence referendum, could simply decline to take part in it altogether. Boycott it. Ignore it completely.

That, it seems to me, is the constitutional choice facing the Scottish Ministers. A meaningful, or decisive, referendum is available to them under the terms of the Scotland Act only with Westminster’s consent. Their choice is either to wait for that, or to press ahead without it, which will mean their actions are unlawful unless so stripped of meaning that the referendum becomes an irrelevance. A meaningful referendum—one which looks and feels and, to all intents and purposes, is—decisive in the manner of 2014 (or 2016) is available to Holyrood only with Westminster’s consent.

The legal obstacles to a second independence referendum are not insurmountable. But getting over them comes at a price—the price being to strip that referendum of any meaning whatever. Perhaps this is why the long wait for the SNP’s IndyRef2 Bill goes on?

Adam Tomkins is the John Millar Professor of Public Law at the University of Glasgow School of Law. He was a Conservative MSP for the Glasgow region from 2016 to 2021. Our columns are a platform for writers to express their opinions. They do not necessarily represent the views of The Herald.