In the mischievous hours on the dancefloor of a rascally Edinburgh nightclub, the leader of the Scottish Conservatives was in spate. A troupe of journalists and politicians had descended after a black-tie event and Ruth Davidson was dismantling common perceptions of conservatism: nothing louche or inappropriate, you understand, just a woman at ease with herself in the company of wolves. Her success in renovating the Conservative brand in Scotland lay a year or two in the future but this night had provided a glimpse of what would propel it.

Until her elevation as party leader, to admit to being a Conservative in Scotland was like owning up to a bondage fetish. The taboo was even taking root in those places where they might once have expected to find safety in numbers: golf clubs, church fetes, Rotary dinners.

Davidson, though, created a safe environment for secret Tories in Scotland. Some of this came about by sheer force of an engaging personality. Much of it, though, was in the story of her personal and political history. She was young, gay and church-going and had enjoyed none of the privileges of education or family connections that first get you noticed in this party. If you insist on voting Conservative in Scotland without being considered a social pariah, this is what you should look like.

For a while, the enchantment held and the apparent Tory revival north of the border reached its apotheosis at the 2017 general election when the Conservatives annexed 13 Scottish seats, an increase of 1,200%. If it hadn’t been for this startling recovery, Theresa May would have suffered more for her hubris in calling that election. Until then, it had seemed that the SNP, whose grip on Scottish politics was strengthened and not diminished by the 2014 independence referendum defeat, were omniscient and infallible. But a combination of the SNP’s own political arrogance and sense of entitlement and Davidson’s cheery tenacity halted the juggernaut.

At this time in Scotland, the three main parties were being led by women from similar non-privileged backgrounds. Exchanges on social media between Nicola Sturgeon, Labour’s Kezia Dugdale and Davidson hinted at a more grownup and respectful way of conducting political business. As Andy Murray marched towards the final of the 2015 Australian Open, the three of them made arrangements via Twitter to skip work and cheer on their fellow Scot. Isn’t this the way we would all like our politicians to behave? Perhaps such enchantment could work at Westminster too with Prime Minister Davidson taking rat poison to the toxic masculinity that contaminates Westminster’s lobbies. This was before the shadow of Brexit, though, and the advent of the Farage/Cummings/Johnson axis – of dark money and Facebook falsehoods; of Little England and Waterloo and Trafalgar. The political casualties of Brexit are propped up like corpses at an Irish wake in the pubs around Westminster and now the contagion has reached Scotland.

Davidson spoke eloquently and with emotion when she announced her resignation on Thursday. She has become a mother and she said that in trying to be “a good leader” she had been “a poor daughter, sister, partner and friend”. Nevertheless, it’s not unreasonable to suggest that she would have continued to find a balance if she could have worked with a Westminster leader whom she trusted and admired. It became clear during the EU referendum, which she fought as a conviction Remainer, that Boris Johnson, in her eyes, was neither of these.

Davidson’s personal attributes secured a good press in Scotland which often bordered on the fawning and this helped deflect a more inconvenient reality: in opposition at Holyrood she and her party were simply devoid of anything resembling a coherent political strategy. She was a far more formidable debating adversary for Nicola Sturgeon than anyone in Scottish Labour but the depth and complexity of her portfolio of ideas ranged from saying No to a second independence referendum to calling the first one nasty and divisive.

Beyond this, there was very little of substance and very little of her that couldn’t be gleaned from contrived photo opportunities in her Territorial Army fatigues and exchanging lines with Paul Merton and Ian Hislop in Have I Got News for You. You formed the impression that she and her chief ally, David Mundell, the ineffectual secretary of state for Scotland, would have contorted themselves into any required Brexit position if it weren’t for the personality and style of Johnson.

Her resignation leaves the Scottish Tories and Johnson’s fledgling administration in a quandary. Right now, they are asking themselves just how many of those 13 Scottish seats really were won by Davidson’s charisma. Will they all disappear again in a puff of the Brexit gas? Already, there is talk of decoupling the Scottish party from its Westminster moorings but those who advocate this must be careful. A second referendum on Scottish independence is now inevitable and the Scottish Tories will once more accuse the SNP of being obsessed with separatism and being divisive. This will be problematic though, if they themselves choose to separate from a UK brand they also consider to be contaminated.

Davidson’s great Tory revival in Scotland has been short-lived, if it really existed at all. Support for a second referendum has grown and, as the hard-right grip on the Westminster Tories tightens, the prospect of a UK without Scotland increases. It seems that so overwhelming is their desire to be rid of Europe that Johnson and his no-deal acolytes will lose little sleep over losing Scotland in the process. Perhaps this thought has just occurred to Ruth Davidson.

• Kevin McKenna is an Observer columinst