NICOLA Sturgeon said something startling about her long-lost plan for a second independence referendum the other day. Asked when the legislation for Indyref2 would be published, she waved away the question by saying it would emerge in the fullness of time. 

What fullness of time, I wondered. The First Minister doesn’t have such a luxury. She has a ticking clock. 

As we all know, and despite Boris Johnson vehemently opposing it, Ms Sturgeon has said she intends to hold Indyref2 by the end of next year. 

As Adam Tomkins wrote here yesterday, that seems a non-starter. Even if the FM passed her own unilateral Referendum Bill, the UK Supreme Court would very well declare it incompetent.

I’m not going to dwell on the wisdom of marching your supporters up and down hills, or looking like a chump when your big finale is an anti-climax. Instead, let’s consider the government mechanics. 

Assuming Mr Johnson doesn’t change his mind, Ms Sturgeon’s stated plan is pass a Referendum Bill and dare the Tory supervillain to do his worst in court. 

Most political commentary takes this as read. But the longer the Bill takes to appear - it was supposed to be out within weeks back in January and still has no date - the more it looks as if something may be holding it up beyond a calculation about when to make a splash with it.

There are a series of legal hurdles to be cleared within government before a Bill can be introduced at Holyrood. 

Critically, it has to be vetted to check it is within the Scottish Parliament’s legislative competence, because anything that goes beyond Holyrood’s powers, even if MSPs back it to the hilt, is just so much nonsense. It is “not law”, as lawyers say. 

If Ms Sturgeon’s Bill fails this early test, all her plans for 2023 are kaput.

As we also know, her government is not big on sharing, especially when it comes to legal advice. But thanks to interview-based research by two legal scholars, Christopher McCorkindale of Strathclyde University and Janet Hiebert of Queen’s University in Canada, we know a fair bit about what goes into deciding if a Bill is competent. 

The vetting is driven by the in-house lawyers of the Scottish Government Legal Directorate (SGLD), who consider if the legislation is “more likely than not” to survive a challenge at the Supreme Court.

Normally, politicians and their special advisers are not involved in this assessment stage, but if there are serious concerns about legislative competence, they may be brought in early to address potential issues, or, in extremis, halt the Bill’s introduction. 

The “more likely than not” test could, in theory, tempt politicians to push their luck with Bills considered a close call. What is meant to stop them overstepping the mark is the role played by the Lord Advocate, the Government’s most senior law officer. 

The Scottish Ministerial Code says that for a Government Bill to be introduced at Holyrood, it must be accompanied by a statement from a minister, “which will have been cleared with the law officers”, that it is within legislative competence. 

That gives the Lord Advocate, Dorothy Bain QC, the power - and duty - to veto an incompetent Bill that can’t be fixed.

The SGLD sends the draft Bill and a note on its legislative competence to the Legal Secretariat to the Lord Advocate three weeks before it is due to be introduced at Holyrood. 

It also sends the material to the Office of the Solicitor to the Scottish Parliament so that the Presiding Officer can take a (non-binding) view on its competence, and to the Office of the Advocate General, the UK Government’s Scottish legal team, who might not agree, but cannot refer a Bill to the Supreme Court for adjudication until after it is passed by MSPs. 

The test the Lord Advocate applies is similar to that applied by the SGLD. 

The Lord Advocate does not have to be satisfied beyond reasonable doubt, the standard in a criminal trial. According to McCorkindale and Hiebert, “based on a civil (balance of probabilities) standard, an assessment is made of how the Supreme Court would be likely to rule on the Bill in the event of a legal challenge”.

The Lord Advocate’s view is also seen as “the end of the matter”, with ministers taking a refusal “on the chin” even if they are unhappy. 

The alternative would be an almighty political scandal. “We were told that the Lord Advocate would see it as a resigning matter” if ministers knowingly pushed ahead with legislation outwith competence, the authors said. 

With a distinguished legal career, a Lord Advocate would value their own independence too much to put up with it; it would offend their belief that governments are subject to the rule of law; and it could leave a stain on their integrity and stop them returning to the bar or becoming a judge. Three of Scotland’s six lords advocate since 1999 have gone on to the bench, after all. 

We know roughly what a Referendum Bill would look like, as a draft version was published last year. It was literally two pages long with a one-page schedule showing a possible ballot paper.

This is because it would piggyback on the more substantive Referendums (Scotland) Act of 2020, which covers the general rules for voting, expenses, and campaigning. 

Any new Referendum Bill would focus narrowly on the aim, question, franchise and ballot paper for Indyref2.

But, despite its brevity, I understand the SGLD has still not sent a final version and note on its legislative competence to the other legal parties who should get three weeks to consider them pre-introduction. 

That suggests the Bill can't be published before June. If it doesn’t appear by summer recess in July, it can’t be laid at Holyrood until September, an extremely tight timetable for a vote in 2023. 

Why the delay? In truth, I don’t know. But as time ticks away, it is becoming curiouser and curiouser.

Of course, it’s not easy trying to second guess the Supreme Court.

But in the three previous cases where the UK Government law officers referred a Holyrood Bill for a definitive ruling on legislative competence, Section 28(7) of the Scotland Act 1998 was pivotal. 

This basically says Westminster still has the power to make laws for Scotland. Any legislation passed by MSPs that would limit Westminster’s absolute sovereignty in any way is therefore outside legislative competence and not law, the Court ruled. 

A Bill intended to deliver independence would self-evidently reduce Westminster’s ability to make laws for Scotland. There’s also the small matter of the Union being reserved to Westminster.

On the balance of probabilities, would such a Bill survive at the Supreme Court? SNP and Green ministers might not mind if it didn’t. Plucky Holyrood thwarted again by the beastly Union, they’d say. 

But the lawyers, and above all the Lord Advocate, who has to make a career-defining call on the likelihood of winning in court, will have their say first. In the meantime, the rest of us keep waiting.