AS ever the nitty gritty of negotiations comes down to semantics.

In the Commons chamber David Davis was asked to explain what the difference was between regulatory convergence and regulatory alignment. His reply: the former led to harmonisation with the EU, the latter did not.

To put it another way, what the UK Government wants is for the UK to make its own decisions on trade regulations but to have the same or similar outcomes to current EU rules regarding trade with the Irish Republic and thus ensuring the border remains soft.

Whitehall sources admitted with a deal of understatement that Monday was “not the Government’s finest day” in the Brexit talks and that more should have been done to stop the hare on regulatory alignment from running for so long.

What it meant was that Theresa May looked humiliated, having agreed a deal with Brussels only for it to be kiboshed and unagreed not because of the likes of Juncker and Barnier but by her Unionist chums at Westminster.

And just when, with a deal of gentle diplomacy, the Prime Minister thought she could win the Democratic Unionists round to a new form of words, up popped Ruth Davidson, pointing out how, having spent so long trying to keep the UK together, she was not going to allow the “thread of the Union” to be unravelled in the Brexit talks. If there were to be regulatory alignment, it must apply to the UK as a whole not just Northern Ireland. Mr Davis in the Commons agreed, insisting maintaining the constitutional and economic integrity of the UK came first above everything else.

So after the DUP’s Arlene Foster dictated the direction of Government travel on Monday, it was Ms Davidson’s turn on Tuesday.

Indeed, Scottish Conservative MPs, while not opposing the Government’s flagship EU Withdrawal Bill, made clear it nonetheless needed to be changed to help maintain devolution and the Union. Expect some changes in the Lords ahead of the legislation going north to get the consent of Holyrood; probably in March.

Politically, the developments of the last 48 hours have shown that a new dimension has opened up in British politics as the Scottish Tories flex their collective muscle at Westminster.

Downing Street sources insisted Ms Davidson’s phonecall to the PM on Tuesday morning, her statement on Twitter about not having separate deals that would undermine the Union, and David Mundell, the Scottish Secretary, stressing the need to maintain the integrity of the UK at Cabinet, were all positively helpful contributions and not in any way critical of Mrs May’s cack-handed negotiation technique.

Or, rather, could it be that Ms Davidson having, like the DUP, seen the UK Government going down a particular route, was horrified that Mrs May was threatening what she herself has called the country’s “precious Union”?

After the dogs have barked and the wheel has been refitted, the Brexit caravan will move slowly on but precisely where it will end up and in what condition is still anyone’s guess.