The plan was for Ruth Davidson to lead the Scottish Conservatives to further electoral gains in the spring of 2021; step down as their leader and leave Scotland’s Parliament; find a Westminster by-election to contest, apparently in Scotland itself; win it; become a Cabinet Minister more or less immediately on arrival in the Commons, win a Tory leadership election in the autumn, in the wake of Theresa May standing down, and then win the general election the following spring.  Win, win, win.

We were always sceptical about this grand scheme.  Why assume that Theresa May will be in place for another three years or so?  Would Davidson win any such by-election?  Is a few week’s experience as an MP, let alone as a Minister, a solid foundation for leading authoritatively and governing well?  Would she still look like a winner if the Scottish Conservatives did not form a government, presumably in coalition with another party or parties?  Above all, could she appeal to what our new columnist, Nick Hargrave, yesterday called the “nation state backers” who “overwhelmingly voted for Brexit”?

Apparently, we will never know.  For this plan wasn’t her own plan – or, rather, if it was, it isn’t now.  “I will not be a candidate,” she says in a Sunday Times interview today.  Politicians can change their minds, and frequently do.  And the headline of an interview doesn’t always justify its contents.  But those six words look like a solid guide to Davidson’s intentions.  Her reasoning emerges from a grisly story of depression, alcohol abuse, nocturnal living, suicidal thoughts and self-harm that took up parts of her younger years.  At one point, she raises “a jacket sleeve to show me her self-harm scars” and the interviewer sees a “pale ivory lattice of scars etched onto her lower arm”.

It is a harrowing story to read and will have been shattering to live through.  We have no window to look into people’s souls, but it is surely significant that Davidson’s decision to give the interview, and provide a fuller account of the story in an autobiography, comes at a time when she is expecting to have a child.  The experience can upend a parent-to-be’s ambitions, image of themselves and worldview.  Cynics will have read the publicity accompanying the run-up to the birth – such as the news that she and her partner had nicknamed their bump “Baby Fionnuala” – as evidence of a slow-burning, carefully-crafted leadership campaign.  It seems that they were wrong.

Where does this leave the hunt of left-of-party-centre Conservatives for a potential leadership candidate?  A lot of Cameroon-flavoured Tories, some of them very senior indeed, see Davidson as their great light-blue hope.  They hope that this offbeat, pawky, taboo-challenging lesbian will transform perceptions of the Party.  As it happens, there is more to Davidson than the kickboxing label.  In some ways, she is a traditional figure as well as a radical one, having served in the TA and projected an uncompromisingly pro-Union appeal for her party: the basis of its electoral gains.  But today, the Davidson option looks closed.

There is far more to Tory differences than former Remainers v Leavers.  For example, Sajid Javid was a remainer but he is in many respects a Thatcherite.  To those who follow the cryptography of these things, Jeremy Hunt was the guest of honour at the Tory Reform Group’s summer party.  But ConservativeHome has seen polling which suggests that his long service at health has hit his popularity hard.  Rory Stewart is certainly a One Nation-flavoured figure.  So is another of our columnists, Nicky Morgan.

So, too, are some of the younger left-of-party-centre Tories – such as Tom Tugendhat, who as good as said last week that younger Tories should provide the next leader (“it is time for a generational shift”), and George Freeman, who fits into that space, and has offered if asked to stand himself.  But with the exception of the Foreign Secretary, all these people have one point in common.  Some are Ministers, others are ex-Ministers, but none currently sit at the Cabinet table. How much does that matter, if at all?