IT’S a subject that simply refuses to go away; the prospect of Ruth Davidson becoming leader of the UK Conservative Party and, potentially, Prime Minister.

Even before she won the Scottish Tory leadership in 2011, the former BBC journalist defied convention. Yet, of course, this was to be to her advantage, particularly in Scotland where the word Conservative had, for many, become a long-standing term of abuse.

When voters thought the Tories in Scotland might choose another besuited, middle-aged, male bank manager type, they got a shock when they opted for a short, gay, ebullient young woman with a down-to-earth squaddie’s sense of humour.

And, boy, has it paid off. The SNP’s unsuccessful drive towards independence has boosted the battered brand of Scottish Conservatism, which grabbed the Union issue with both hands and has benefited from Scotland’s polarised politics.

Look what happened in June. Having been wiped out in Scotland 20 years ago and having muddled along with just one MP for years and years, the Tories now have 12 disciples to aid David Mundell, for so long the singular Scottish Secretary. Panda jokes have been banished to political history.

And all the time the stock of the telegenic Ms Davidson has risen. Just as during the recent UK elections Ms Sturgeon impressed left-leaning voters south of the border, so too the Tory leader in Scotland won fans among the Conservatives of England.

For the last few autumn gatherings of the UK Tories, the Edinburgh MSP has been the darling of the conference; invariably having the honour of being the warm-up act for the UK party leader’s set-event on the closing day.

After the independence referendum, one Cabinet minister admitted that Ms Davidson was now being seriously viewed by many as a future UK leader. The argument goes that if the non-stereotypical Tory could do what she has done north of the border, think what she could do south of it.

Interestingly, the Scottish party leader once used to rule out categorically any thought of leading the UK party but has more recently hinted that one day it might, just, be a possibility.

Yet, having led the party to winning 13 seats in Scotland, the party’s best performance since 1983, Ms Davidson has her eyes firmly on Bute House and replacing Ms Sturgeon as First Minister.

Scottish colleagues at Westminster look askance at the suggestion of their leader being parachuted into an English constituency to replace a doomed Theresa May in 2019. Such a move would, they argue, send a terrible signal about the value Tories placed on Scotland.

So for now it looks a non-starter. But Ms Davidson is only 38. Time is on her side. As many more seasoned politicians have come to learn: you never say never in politics.