Theresa May's Scotland visit timed to bolster the Union

While the Prime Minister has, understandably, not made public who she wants to see as her successor, she does not have to; the answer to the question is blindingly obvious.

So, on Thursday Mrs May, who made her first visit as PM to Scotland, will make her last one north of the border to underscore her love for her “precious Union”.

The Herald was once told that when on the first day she took over in Downing St her desk in-tray was piled high with folders marked with various subject matters. The one marked “United Kingdom” had been placed at the bottom of the pile. The new premier frowned, pulled it out and placed it right at the top.

• READ MORE: Theresa May issues plea over future of the Union

In the last few days, Mrs May has had to endure the sight of the two contenders rubbishing her approach to Brexit and dancing on the grave of her failed attempt to get Brexit through; even though both of them backed her Withdrawal Agreement in the final Commons vote.

Her speech on Thursday will be scanned for any nuance that can be interpreted as a put-down to one candidate or an endorsement of the other; in other words, Boris for the former and Jeremy for the latter.

No doubt, alarmed by the “do or die” rhetoric of Mr Johnson, Mrs May’s central message about strengthening the Union will be directed at her former Foreign Secretary. Watch out to see if there are any references to charging at the guns and the Valley of Death.

In the last few days and, no doubt, in the next 48 hours before the Scottish hustings, the two would-be premiers will be busy burnishing their Unionist credentials.

Just as there has been a bidding war on fiscal promises and on who can sound the hardest on a no-deal Brexit, so we can expect the two contenders to be trying to out-speak one another on who is the greater Unionist.

Mr Hunt has already pronounced that he would support the Union with "every drop of blood in my veins". At Tuesday’s Belfast hustings, when talk was of the backstop and borders, Mr Johnson declared the “Union comes first" and was “absolutely inviolable”.

Both men have committed to introducing a Union Unit in No 10 to better co-ordinate the Unionist message across Government.

With time so short before she goes, the PM’s attempt at legacy-building is difficult if not impossible. And yet this newspaper has been told that she will soon announce a review, possibly in her speech on Thursday in Scotland, to look at how the Government structures can be configured to strengthen the Union; the very subject of her final address.

The Conservative administration is due shortly to publish its response to the Commons Scottish Affairs Committee report on constitutional matters, which called for a review of the role of the Scottish Secretary and Scotland Office now that we are 20 years on from the start of devolution.

• READ MORE: UK Government under attack over Jeremy Corbyn health claims

While the Nationalists want the post and office abolished, some Unionists want them to be subsumed into a Department for the Union headed by the Deputy Prime Minister or First Secretary of State.

But David Mundell has been, behind the scenes, battling to have the role enhanced. Indeed, there are suggestions the Scotland Office is going to be beefed up with a couple of new ministers as part of the underpinning of the Union.

The Scottish Secretary is due to appear before the committee next week when he will doubtless expand on his vision for his office; which, of course, might not include him depending on who wins the Conservative crown.

Other signs of strengthening the Union are the UK Government’s new hub in Edinburgh, including a dedicated room to enable the UK Cabinet to hold some of its meetings there, and a push for more direct Whitehall funding of Scottish projects in devolved areas; denounced as a “power-grab” by Edinburgh.

One Unionist project, however, is unlikely to see the light of day: Mr Johnson’s idea of building a bridge between Scotland and Northern Ireland.

When asked about it, he insisted he was still supportive but noted diplomatically it was something for the Northern Irish Executive to take forward. Which means another “Boris bridge” will never see the light of day.