I DON’T blame you for avoiding your crystal ball these days, when the leering, bantering, burbling face gazing back at you, under its fuss of hair, is Boris Johnson’s. But with such a fantastical future solidifying around us, as Scottish Tories make shameless accommodations with their new reality, I want you to consider one way the SNP and Greens could radically alter the political weather.

Scottish politics is approaching a crunch point. There is a pro-independence majority in Holyrood. A broad statutory framework for a referendum will shortly be in place. The Tory leadership contenders have taken up Theresa May’s cry that “now is not the time”, arguing they “won’t allow” a second independence referendum.

None of the candidates has shown any insight into how the present divisions in British politics might be reknitted. Thanks to the indiscipline and inconstancy of the Labour Party, serious attempts to forestall crashing out of the EU on October 31 without a deal continue to fail, and fail, and fail.

This week, we’ve heard at least the third iteration of Ruth Davidson’s ideas on what might constitute a clear mandate for a second independence referendum. She told BBC Scotland if Nicola Sturgeon “puts it in a manifesto that she’s going to hold another referendum and she wins a majority outright, then she can negotiate with the UK Government in the same way as happened last time”.

With all the talk of an early Westminster election to try to break the Brexit deadlock, it’s perhaps surprising nobody seems to be speculating about parallel developments north of the Border. While the timing of the next UK election is seen as tactically contingent and mutable, the next Holyrood election is generally presented as fixed in stone, and all Nicola Sturgeon can do is navigate her plans around it. Not so. Or not necessarily so.

Historically, UK prime ministers enjoyed the power to call ambush General Elections whenever the winds of politics seemed to be blowing in their favour.

In calling the calamitous 2017 General Election, Theresa May joined a series of statesmen and women in British politics who’ve misjudged the political weather and launched their skiffs into stormy waters. Instead of the plain sailing they anticipated, many British political leaders have found themselves suddenly in the grip of invisible currents and undertows in rejigging the parliamentary timetable. Others have been rewarded for their audacity.

Harold Wilson’s snap poll in 1966 worked in his favour, transforming his tissue-paper majority over the Tories into a workable lead in the Commons. Ted Heath’s surprise victory over the Labour leader in 1970 presented a more sobering lesson. Gordon Brown must still regret the “General Election that never was”.

Westminster’s much-abused Fixed-term Parliaments Act was meant to rip this arbitrariness out of the British electoral cycle, constitutionalising the timetable for elections, rather than leaving it up to prime ministers to game the system in their own interests. Under its provisions, UK General Elections would fall on a predictable cycle, with polls on the first Thursday in May every five years.

But the legislation incorporated political safety valves. The five-year cycle can be set aside if two-thirds of MPs vote for it, or alternatively, if a simple majority of MPs pass a motion saying they have “no confidence in Her Majesty’s government”. The Scotland Act contains similar rules. Its framers envisioned Holyrood elections would follow a steady four-year cycle. But like the UK law, there are workarounds.

So how could a snap Holyrood election be called? There are two potential triggers. Firstly, if two-thirds of MSPs vote to dissolve Parliament, an election must be held. In simple terms, this needs a supermajority of 86 of Scotland’s 129 MSPs. While Holyrood has a simple majority in favour of a second independence referendum, the combined forces of the Greens and the SNP fall well short of two-thirds of the total parliamentary roster.

They couldn’t force the issue alone. The motion would need the support of either the Labour Party or the Tories to pass. In Westminster in 2017, Theresa May got over this hurdle with Jeremy Corbyn’s backing, who – then as now – claimed to be champing at the bit to return to the polls. Challenged to accept such an early election, what would Ruth Davidson and Richard Leonard say? “Bring it on”? “Now is not the time”? “We said no and we meant it”? The lack of a pro-referendum supermajority may make this ploy look like a non-starter.

But look closer. There’s a second way Nicola Sturgeon could bring this Holyrood term to an early end. And there’s no obvious way the opposition could resist it. Under section 46 of the Scotland Act, Holyrood must nominate one of its members to serve as first minister after a General Election, or if the post falls vacant. If MSPs can’t agree on who should serve, the Scotland Act returns the question to the people for a fresh mandate.

In 2007, the SNP won 47 seats to Labour’s 46 – both minority positions. Only Jack McConnell and Alex Salmond put themselves in the frame for the top job. The LibDems and Tories abstained in the vote, giving the SNP leader a narrow majority in the run-off, installing the SNP leader in Bute House. In 2016, only Willie Rennie stood out against Nicola Sturgeon for the role, who sailed through with 63 votes to the 5 cast for the LibDem.

So what would – could – happen if the SNP decided the UK Government’s constitutional attitude was intolerable, and Nicola Sturgeon were to resign to seek the kind of irresistible mandate for a second referendum Ruth Davidson was havering about this week?

Here things get a little weird, because of Holyrood’s standing orders, and how votes to select the FM work. Bear with me. If there is only one candidate for First Minister, MSPs are given the opportunity to cast votes for, or against them – or to abstain. The solitary contender needs a simple majority of votes to win.

If there are more than two candidates, run-offs will continue until we’re down to the final two. And, critically, in this final, two-way run off, MSPs aren’t given the opportunity to cast negative votes. The presiding officer only tallies votes in favour of the remaining candidates – or abstentions. Discounting any abstentions, in this scenario whichever one of the duo receives the most positive votes becomes first minister.

Run my hypothetical scenario through these rules. If Ruth Davidson presented herself as the solitary replacement for Nicola Sturgeon, she’d be voted down. But if the SNP declined to put forward a candidate for FM, we could be reduced to the ridiculous spectacle of a Davidson-Leonard contest, and the Tory leader being anointed first minister with just 31 positive votes in a 129-member chamber.

What would inevitably follow is complete ungovernability. Ministerial appointments, refused. Motions of confidence against the new FM, easily carried. While the Tories and Labour may instinctively – initially – be inclined to resist any attempt by the combined forces of the SNP and Greens to bring down the roof on this session of parliament, their scope to do so realistically is extremely limited if Nicola Sturgeon set this dramatic process in train.

Would she? Could she? I leave you to contemplate the political wisdom of this. The risks are obvious. The history books are full of politicians who have been both punished and rewarded for such gambits. We know independence powerfully mobilises those who support, and those who are against it. We know that for the foreseeable future, the Unionist vote in Scotland is divided in parliamentary terms, to the SNP’s advantage. We don’t know how the public would react to putting the constitution front and centre in a Holyrood election.

But as UK politics blows up, as independence supporters consider all the realistic democratic alternatives to make a break with this broken United Kingdom, it’s worth remembering that it isn’t just Boris Johnson who can go nuclear.