Readers of this column will be aware that the Scottish Conservatives have shown signs of strategic confusion in the run-up to the (now postponed) ‘meaningful vote’ on Theresa May’s withdrawal deal.

This culminated in David Mundell and Ruth Davidson both threatening to resign if the Prime Minister gave way on the EU’s demands for differential treatment for Northern Ireland… only to perform a screeching u-turn when she did, in fact, give way after all.

Aside from a nasty barb about ‘carpet baggers’, the justifications offered to support this shift (to the extent that it was acknowledged as a shift at all) were deeply unconvincing. Whilst talk of a ‘union state’ might have served as a reason not to worry about the backstop in the first place, it doesn’t justify dramatically changing one’s mind on it in the space of a month.

Given the paucity of plausible reasons for the change of heart, and the sheer unexpectedness of their initial threats to resign, one possible explanation does suggest itself: pitch-rolling.

By putting down markers about their staunch opposition to the deal on unionist grounds, and then backing it, Mundell and Davidson could use their unionist bona fides to shield May and shut down her unionist critics.

That’s only conjecture, of course, but it is worth bearing in mind as we consider the next strange development in this story: the surprise rebellions of John Lamont and Douglas Ross against the Withdrawal Agreement.

Why is this a surprise? Because both MPs are on the ‘Davidsonite’ wing of the party. Lamont used to be her chief whip in the Scottish Parliament, and was one of the architects behind the Scottish Tories’ now-disintegrating pooled-staffing arrangement at Westminster. Ross, meanwhile, has been talked about in some quarters as her preferred successor, at least before he got into Parliament.

All the evidence suggests that this tendency is backing the withdrawal deal. Adam Tomkins MSP, a constitutional law professor and close ally of Davidson, has been sent out to claim that the unionist case against the backstop has been ‘destroyed’ (spoiler: no it hasn’t) and Paul Masterton, another ally and the MP who helped coordinate the Holyrood powers-grab during the passage of the Withdrawal Act, has joined in Mundell’s attacks on “English nationalists” playing at unionism.

Yet all of a sudden Ross Thomson, who had until now been ploughing a very lonely furrow as the sole Scottish Conservative rebel on the Withdrawal Agreement, finds himself joined not by any of his colleagues who have previously supported European Research Group manoeuvres (Colin Clark, Alister Jack, and Stephen Kerr to name but three) but by these two loyalists.

If you subscribe to the ‘cock-up’ view of the Mundell u-turn, this is evidence that this wing of the Scottish Tories is losing its strategic cohesion in a really remarkable way.

But there are also a couple of reasons not to discount the ‘conspiracy’ version: that this is a second round of pitch-rolling, with Lamont and Ross preparing to ‘do a Mundell’ in order to give whatever form of words the Prime Minister comes back with some credibility. Neither declared their hand until after the Government had pulled the ‘meaningful vote’ on Monday morning, nor has either been explicit about what changes they would need to see in order to support the deal.

Whatever the truth of it, however, this decision poses sharp questions for their colleagues. Opposition to the deal on unionist grounds can no longer be presented as a mere flag of convenience for committed Brexiteers.