Geoffrey Cox has stepped once again into the public eye this week with his warnings about how any ‘temporary’ Brexit fix to dodge the Irish backstop could too easily become permanent.

Thus the Attorney General, who at one point looked like the man to sell Eurosceptic colleagues on the virtues of Chequers, is now the focal point of a fresh round of Cabinet unease about Theresa May’s proposals.

But the real problem with the backstop is that hostility to it runs farther than the European Research Group/Democratic Unionist axis. Both Ruth Davidson and David Mundell, the leading figures in the Scottish party and neither of them a Brexiteer, are also deeply opposed.

It isn’t difficult to see why. Whilst neither of them wanted to leave the European Union, each is a Unionist first and foremost and wants to avoid a form of Brexit which would offer a boost to the SNP. Much to the surprise of many commentators the mere fact of the Leave vote has not helped the Nationalists – far from it – but that doesn’t mean that the wrong exit deal couldn’t give Nicola Sturgeon a vital lifeline.

A Brexit deal which fractured the UK internal market and offered one of the Home Nations the opportunity to stay inside important components of the EU – especially if it also somehow maintained near-frictionless trade with the mainland – would make it much more difficult to resist demands from the Scottish Government for similar treatment. Even if Westminster held firm, the prospect of Scots having their cake and eating it with a similar “best of both worlds” arrangement could prove a difficult myth for unionist parties to combat.

It would also undermine the idea of the United Kingdom as an integral state, which Mundell in particular has been keen to stress, and bolster those keen to present this country as a sort of mini-EU or other mere multinational arrangement.

Davidson will be leading her troops into the next Holyrood elections in 2021, in the midst of whatever the UK’s transition out of the EU ends up looking like. She will want to be able to point to some clear Brexit gains for Scotland – such as departing the Common Fisheries Policy – but it would surely not serve the Tories’ prospects were the entire campaign to be dominated by the question of whether or not Scotland could or should have been allowed to stay half-in the EU.