Scottish Tory leader Ruth Davidson has long had a band of cheerleaders in both Scotland and the wider party. But she achieved true crossover appeal during the EU referendum campaign, when the upbeat Remainer confronted overambitious Brexiteer Boris Johnson during a TV debate, and pretty much called him a liar.

In the aftermath of Brexit, and the disappearance of the Cameroons, she became a guiding star for liberal Tories unwilling to stomach an increasingly nativist government.

In Scotland, though, where opposing Brexit is a matter of course for mainstream politicians, Davidson stands out because of her unionism. As I reported in April, her strategy of uncompromising opposition to independence helped her gain supporters across Scotland, even in Labour citadels like Paisley. This culminated in the snap election of 2017, when Davidson sent 12 new Scottish Tory MPs down to Westminster. It was enough to help the minority Tory party form a government, with a confidence and supply arrangement with the Democratic Unionist Party.

Now, the Irish border question – which pits Brexiteers and hardline unionists against the EU and more pragmatic elements of the UK government – is placing the two forces that propelled Davidson's career into opposition. Her way of resolving that challenge is a reminder that, while the Westminster government may have squashed Scottish independence, Davidson has considerable clout from her position in Holyrood, and a Brexit-related constitutional headache is never far away.

So far, despite Davidson’s clear differences with these other unionists, she has mostly restricted her criticism to the DUP’s record on LGBT rights. The Irish border question, though, is becoming harder to ignore. When it appeared that the UK government was on the brink of conceding to the EU and allowing Northern Ireland to stay in the single market and customs union, the news was seized on by Scottish first minister Nicola Sturgeon, who tweeted: “If it’s not some kind of Norway status for whole UK, it must mean some kind of special deal for NI. Has to be one or the other. And if latter, why not also for Scotland, London & Wales (if it wants it)?” Hours later, an intervention from the DUP leader Arlene Foster meant no deal was announced.

The Irish question pits Davidson’s unionism against her desire for a soft Brexit. In a statement on Tuesday morning, she noted the question on the ballot paper – whether the UK should stay or leave the European Union – a seemingly innocuous observation which is nevertheless a reminder that voters never directly chose to leave the single market or customs union. Davidson said this meant voters were not asked “if the country should be divided by different deals for different home nations”.

She continued: “While I recognise the complexity of the current negotiations, no government of the Conservative and Unionist Party should countenance any deal that compromises the political, economic or constitutional integrity of the United Kingdom.”

Nevertheless, she added that there “should be no return to the borders of the past”, concluding: “If regulatory alignment in a number of specific areas is the requirement for a frictionless border, then the Prime Minister should conclude this must be on a UK-wide basis.”

As a Tory Davidson’s attempt to use the crisis to push for a softer Brexit UK-wide is hardly surprising, given her consistent emphasis on the importance of trade. But read between the lines, and one of Scotland’s most canny unionist politicians is making much the same case as her ideological opponent, Sturgeon, but as Kenny Farquharson points out, arguing it much better. Every single region of Scotland voted to remain in the EU in 2016. Davidson’s comment is the latest reminder of that fact.