I STILL like Donald Rumsfeld’s nifty formulation of “known knowns,” “known unknowns,” and “unknown unknowns.” They can be helpful framework for strategic thinking.

Last week, the Scottish ­Government published the first in a series of policy papers on independence. ­Entitled Independence In The Modern World, the paper’s key argument is that countries of Scotland’s size have consistently outperformed the UK across a range of ­economic and social indicators. The publication marks an important but belated shift – from a debate about having a referendum, to thinking about what kind of arguments the Government would make in a second campaign.

But the process arguments haven’t gone away. The publication has resulted in a ­flurry of headlines and pull quotes which take us right back to where we started – to questions about legality, process, ­challenges and timelines.

I want to give you some critical tools to make sense of what you’re seeing – and a better understanding of the legal break points involved. To put it another way: let’s walk through some of the known knowns and the known unknowns facing any ­second referendum bid.

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We know there is a comfortable ­majority in the Scottish Parliament for a second referendum. The challenge, therefore, is not passing the bill – but getting it into ­parliament in the first place and out the door in one piece. You might think this is a purely political calculation. You’d be wrong.

Let’s start at the beginning. For a ­referendum to take place, parliament will have to authorise one through legislation. We know that the Lord Advocate is the Scottish Government’s chief legal adviser. We know that before lodging any bill in ­Holyrood, ministers will consult Dorothy Bain QC on the legislative competence of the measures they’re proposing. We also know her legal advice is privileged – which is to say, is not usually put in the public ­domain.

Section 31 of the Scotland Act says that any MSP introducing a bill to Holyrood must “state that in their view the ­provisions of the bill would be within the ­legislative competence of the Parliament”. The ­Presiding Officer has a role here too. On the introduction of a new bill, Alison ­Johnstone will have to make a public ­statement about whether she believes its provisions are within competence.

The Presiding Officer’s statement is based on independent legal advice – and experience has shown us that ­Presiding ­Officers can be wrong. In the past, ­Johnstone’s predecessors greenlit ­provisions which were subsequently found to be outside competence by the courts, and wrongly concluded ­legislation like the Brexit Continuity Bill were ­problematic.

The same goes for Lord Advocates past and present. I mention this just to stress a point which may not always be obvious – making calls on legislative competence can be tricky and contested. Laws aren’t always straightforwardly black or white.

What happens next may come down to that phrase – “would be within ­competence”. I know this is why folk hate lawyers – but bear with me. Does this mean the MSP lodging a ­referendum bill must be satisfied their bill is ­definitely within devolved competence? What about arguably so? Would legislation which was maybe within competence ­suffice to make the declaration? Any of the ­Scottish ­Ministers introducing referendum ­legislation will be doing so based on advice from the Lord Advocate – and the new Lord Advocate’s appetite for ­legal risk is one of the big known unknowns in play here.

Until a court decides otherwise, my view is that it is arguably within ­Holyrood’s competence to legislate for a referendum about Scotland’s constitutional future without Westminster’s consent – but it is nowhere near a sure thing. The Scotland Act says that we need to consider the “purpose and effect” of a piece of legislation in deciding whether or not it “relates to a reserved matter”.

While the Union is a reserved ­matter, referendums as such are devolved. And there are different and credible ways of describing what a referendum on ­independence is for. The case against ­competence says any indyref2 is ­inevitably about the breakup of Britain. The case in favour says that referendums in the UK have no legal ­effect – that they’re essentially ­advisory – and that their purpose and ­effect sound in the political rather than the legal domain. But will these ­arguments be enough to persuade the Law Officers to give a referendum bill the go ahead? We don’t know.

But say, for the sake of argument, that Dorothy Bain proves risk averse and tells Scottish Ministers she can’t sign off a ­referendum bill as within competence. What then? There are other options which can then be contemplated to get a bill into the chamber. The Lord ­Advocate is the Scottish Government’s lawyer. She doesn’t advise the parliament or ­individual MSPs – and every parliamentarian has the right to propose legislation for the consideration of their colleagues. This sidestep raises opportunities for ­other surprising interventions.

If the Lord Advocate advised the Scottish Government she thought a referendum bill was potentially outside competence – but the bill was introduced and passed anyway – what would she do? Before bills receive royal assent and become law, the UK law officers – and the Lord Advocate herself – can refer legislation to the Supreme Court for scrutiny. Would she decide to do so? Another known unknown. And what about the UK Government? Would they try to stymie the process in the Supreme Court?

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There has been speculation for some time that the UK Government might not want to take the political hit by litigating. I have my doubts about that. If the UK Government is happy to legislate about devolved matters time and again ­without consent and ignoring dissent, if they aren’t worried about going to law to limit the impact of children’s rights in law, it seems unlikely to me that they’d mind being seen to stomp all over Scotland’s democratic institutions when it comes to our constitutional future.

But for the sake of argument – say it suits the UK Government to find a wealthy litigant who could do the work for them, entangling any referendum in the courts but relieving London of the ­primary ­responsibility for ­attempting to block a referendum mandated by a ­majority vote in Holyrood after an ­election mandate. Step forward Robert Kilgour, who is just the kind of character calculating ­Unionists had in mind.

Kilgour is executive chairman of ­Renaissance Care and a founder of the pro-Union group Scottish Business UK. He spoke to the Daily Mail last week, suggesting that he and “like minded ­businessmen” would take to the courts to challenge any referendum bill.

“The UK Government have their own reasons for not rising to the bait but there is no reason why a group of us in ­business shouldn’t challenge her on this,” he said. The paper also raised the ­prospect of a ­pre-emptive strike, suggesting that while “the UK Government would only ­challenge legislation after it passes at ­Holyrood whereas private individuals could launch an action as soon as any proposed legislation is published”.

Is this true? Well, yes and no. As the Court of Session held in the People’s ­Action on Section 30 judicial review, ­until a final draft of any legislation is passed by the Parliament at stage three of the ­scrutiny process, any challenge is likely to look “premature and hypothetical”. It is the court’s job under the Scotland Act to judge whether the legislation which has been passed strays beyond Holyrood’s powers. You can’t do that properly until you have a final text to work with. To that extent at least, the Kilgour intervention seems a bit previous. But there is other mischief which might be made. To see the opportunities for Unionist campaigners running interference, you need to know a bit about the history of devolution.

In November 1999, a group of fox ­hunters sued Mike Watson. Watson was then a Labour peer and the sitting MSP for Glasgow Cathcart. But in 1999, ­Watson wanted to introduce a private member’s bill to abolish the hunting of mammals. He’d taken on a full-time ­researcher – funded by the Scottish ­Campaign Against Hunting – and registered this interest with the parliament.

Jeremy Whaley sued, seeking an ­interim interdict preventing the MSP from ­introducing his bill. While Lord Rodger held that “the court could not grant an ­interdict against the Parliament ­considering a bill”, or “against the ­Presiding ­Officer granting the necessary certificate of ­legislative competence” – he left open the possibility that individual MSPs could be interdicted in the courts from presenting a bill to Parliament. Twenty years have gone by without a ­similar incident, but Whaley v Watson is still good law.

This is another ­dimension of ­Holyrood’s fragile parliamentary ­privileges – and a legal vulnerability which a ­freelancing, well-funded lobby group might be ­tempted to exploit.

Expect the unexpected, and let the ­chicanery begin.