In deciding to try and tough out demands for Dominic Cummings’ resignation, the Prime Minister has turned his Chief of Staff’s fate into a trial of strength between himself and his administration’s various foes.

But criticism is not confined to the Government’s opponents. Polls show majorities of both Conservative and Leave voters back his dismissal. A growing number of Tory MPs have called for Cummings to go.

Douglas Ross, the MP for Moray, has gone further, resigning from the Government rather than defend Boris Johnson’s decision to his constituents, as he would have been obliged to do as a junior minister. This ought to worry the Government more than it does.

Whilst Downing Street sources are dismissing Ross as a ‘Mr Nobody’, many Scottish Tories are seriously concerned that whether Cummings stays or goes is a test not just of the Prime Minister’s strength, but of his commitment to the Union – and the consequences of failure could be catastrophic.

Anyone who remembers ‘Operation Arse’, their ill-fated effort to bar his path to Number Ten, will know that relations between the Prime Minister and the Scottish wing of the Party have never been stellar.

But that hasn’t stopped them working with him over the past year. Those I spoke too were keen to stress that the current row is not simply about re-fighting old battles. Perhaps this is why Ruth Davidson, whose antagonistic relationship with Johnson was well known before she resigned as Scottish leader, has broadly kept her counsel – to prevent serious strategic concerns being written up as a soap opera.

In fact, the reasons pushing the Scottish Conservatives over the trenches on Cummings are much more acute.

First, there is a quite reasonable fear of looking like hypocrites. The Party was extremely vocal in pressing Nicola Sturgeon to dismiss Catherine Calderwood, her Chief Medical Officer, after the latter was caught breaking lockdown to visit her second home. The First Minister was eventually forced to do so, after an ill-judged attempt to keep her on, and MSPs felt they could not apply another standard to Cummings.

But the much bigger problem is that the perceived problems with the UK Government’s response, especially with regards to messaging, is making it extremely difficult for the Tories to hold the SNP to account for their mishandling of Covid-19 in Scotland.

The Scottish Government’s record ought to be a target-rich environment for the leading opposition party. Scotland’s care home deaths are an emerging national scandal; the SNP has not once hit its testing targets; it has lagged behind England recruiting trackers and setting up supermarket deliveries for vulnerable citizens; and much more. On the big-picture stuff, meanwhile, it has broadly followed the same approach as London.

Yet as Johnson’s ratings dive, Sturgeon has so far managed to maintain the rally-round-the-flag poll bounce. Both she and her administration are extraordinarily popular, a fact the Scottish Tories attribute to the First Minister’s comprehensive victory in the messaging game. Contrast Sturgeon’s press conferences with comparable performances by Johnson or Matt Hancock, and remember that many voters only really engage with stories on that level, and the problem is obvious.

The Cummings story, Conservative strategists fear, may be a moment that ‘crystallises’ a growing sense, across a broad swath of the Scottish electorate, that Edinburgh is outperforming London. A sense that will be no less damaging to the Party or the Union for its being, in policy terms at least, false.

It’s true that the Tories don’t have the luxury of four years’ breathing space, facing as they do Holyrood elections scheduled for 2021. But some see the challenge as much more existential than that. An SNP/Green majority next year creates a strong (if not insurmountable) mandate for another referendum on independence, one in which popular perceptions of Westminster’s poor handling of the Covid-19 crisis could play a pivotal part.

The pandemic ought to be an opportunity to demonstrate the utility of the Union, not least via the awesome firepower of the Treasury. It would be extraordinary if, having navigated Brexit without handing the Nationalists the opening they anticipated, the Government were to hand them another.

But do they really care? North of the border, there is a growing sense that the current administration do not take the Union especially seriously – and that Cummings is part of the problem. Brexiteer MPs who recently learned they have voted to introduce a trade border between Great Britain and Northern Ireland, on the basis of blithe promises from Downing Street that it could be scrapped later, may share their suspicions.