Jackson Carlaw’s resignation as leader of the Scottish Conservatives yesterday took everyone – except those who engineered it – by surprise.

Only six months into his role, he was helped to come to the decision that he was not the man to save the Union in the Scottish Parliament elections scheduled for May next year. Dismay at his failure to chip away at Nicola Sturgeon’s utter domination of the Scottish political landscape during the Coronavirus crisis was widespread in the Scottish party. Internal polling was dire for him and this was used to bring matters to a head by Lord McInnes, the party’s director, who is a data-driven campaigner.

An additional factor in the mix is the newly formed Alliance for Unity, an extremely broad church being brought together by that most unlikely of clergymen, George Galloway, in which considerable differences are being put aside in order to defeat the SNP. Scottish Labour, LibDems and Conservatives all see the utility of such a movement, whilst also fearing what it could do to drain away their own claim as bulwarks of the Union.

Given that only six months ago Carlaw secured three-quarters of the vote of party members in a two-horse leadership election, this is a coup. Most of Carlaw’s frontbench colleagues found out about it by Twitter and radio reports – so we can narrow considerably the number of conspirators.

Whilst the decision to strike before it was too late was initiated from within the Scottish party, it fits in with the increasing sense of urgency animating the government in Whitehall that the Union now needs saving (and it really is a matter of saving it, not bolstering it). The Prime Minister has charged the Cabinet Office minister, Michael Gove, to think strategically about what to do about winning back Scottish hearts and minds, a role that in calmer times might reasonably have been left to the Secretary of State for Scotland, Alister Jack. Downing Street approved the coup, but did not start it.

The conspirators have struck with deadly efficiency. The dagger wound is clean, all but invisible. The choreography with which Carlaw’s self-effacing statement was swiftly followed by that of his more successful predecessor, Ruth Davidson, announced that she would step-in as the Tories’ spokeswoman to tackle Sturgeon in Holyrood, shows that the switcheroo was planned with the military precision and secrecy that comes from not taking too long and involving too many individuals at the planning stage.

The ruthlessness of it all will reassure those who wondered whether the Conservatives – north and south of the River Tweed – still had what it takes to succeed in Scottish politics. This was brutal. But whilst there is considerable sympathy for Carlaw at a human level, nobody is today speaking up about it is a mistake.

this is a coup.

Yet, it leaves much unclear. Although her destiny to sit in the House of Lords has now been postponed until after May, Ruth Davidson is adamant that she is only standing-in to face Sturgeon at First Minister’s Questions until May’s Holyrood elections. She is not reapplying for her old job. She is apparently not even keen to be styled “interim leader” – even although that is how she will be perceived.

Whilst even those who don’t much care for her outspoken shtick agree that she is by far the Scottish Tories’ best hope of rallying support for 2021, it is less than ideal that her party will fight the Holyrood elections with a campaign that will be largely fronted by someone who is not herself standing in it. Nationalists will hammer this point home, relentlessly.

The plan is that in the meantime the 37-year-old Douglas Ross is manoeuvred into being the Scottish Tories’ next leader. He has already announced his intentions in a WhatsApp message to fellow MPs. Let it not be said he let’s the grass grow under his feet.

But, not so fast! There is no constitutional obligation for a Scottish party leader to be a Holyrood MSP (there was a prolonged time when Alex Salmond got away with not being one), but in reality this has now become all but a requirement. The problem is that Ross has not been a Holyrood MSP since 2017. He will therefore have to stand down as the MP for the super-marginal Westminster constituency of Moray which he has held since 2017. This he cannot do immediately. There is no vacancy at Holyrood. So, he will have to wait until May to do so (standing on the regional list), at which time there will have to be a by-election in his Westminster constituency. It will therefore be difficult for him to emerge from Davidson’s shadow before he has properly transitioned from one parliament to another.

And what of the constituency he will have to surrender? Situated in the north-east of Scotland, Moray is a predominantly rural constituency around Elgin and the RAF base at Lossiemouth. It has favourable demographics to remain Tory – it was even only 0.1 percent away from recorded a majority for Leave in the 2016 Brexit referendum, which puts it in very atypical Scottish political territory. But the seat was continuously held by the SNP from 1987 until Ross toppled Angus Robertson there in 2017. Last December, Ross clung on against a resurgent SNP challenge by the slender margin of 513 votes. Would his replacement win a by-election there? If not, then that is the Scottish Conservative contingent at Westminster down to five MPs.

That will, of course, be a price worth paying if it means the Scottish Conservatives gain a full-time leader (it is still unclear just how part-time Davidson will be between now and May). But the Nationalists’ will struggle to paint Ross as a privileged highland laird: he was educated at a local comprehensive school before studying agriculture and working in (rather than owning) a dairy farm; he is a qualified football referee and was one of the officials at the 2015 Scottish Cup final. Indeed, he faced criticism for wanting to continue refereeing matches at the weekends after he became an MP. With an attitude like that he could even possibly pass the “normal” test that appeals to voters otherwise sceptical of the political class.

That is a start, but it is far too soon to foresee what sort of leader he might make. No sooner had he begun to take government responsibility than he relinquished it. Nine weeks ago he resigned as a parliamentary under-secretary of state at the Scottish Office over Dominic Cummings’ peregrinations during lockdown.

Now it seems Downing Street and the Cabinet Office regard him as the best hope. No encouragement will be given to other contenders to stand – unless, of course, Ruth Davidson can yet be persuaded to change her mind, reapply and refight her Edinburgh Central constituency for Holyrood in May. If she did, it would be a high risk for herself – her SNP challenger would almost certainly be Angus Robertson (the SNP National Executive having found a way to prevent his pro-Alex Salmond rival for the nomination, Joanna Cherry, from standing for the seat whilst she is still a Westminster MP). If Davidson lost, there would still be the peerage as a consolation.

There is no certainty that the Scottish Conservatives have found a solution. But yesterday they took a bold step in demonstrating they realise they have a problem. That opinion poll in July showing 54 per cent support for independence has certainly concentrated minds.