The Tory leader Ruth Davidson is once again a voice of sanity

Sir Jeffrey said: “We are making progress on Brexit with our discussions with the government and therefore I think it is unlikely this situation will arise.”

It is hard to see a way out of the crisis that does not involve an overhaul of December’s backstop or its scrapping altogether, as Boris Johnson advocated on these pages at the weekend.

Dublin, fully backed by the European Union, has made clear that there can be no regulatory or customs divergence on this island at any time. That is the logic of its position.

If this is agreed, Northern Ireland will never be able to diverge from (and therefore leave) two central pillars of the EU.

Wording that reaffirms a determination to avoid a hard land border is one thing, legally prohibiting it forever is another.

It would be a massive betrayal if UK desire to placate a neighbouring state meant that in part of its territory it gave precedence to the prevailing regulatory standards in that adjacent state over the standards that prevail within the UK.

If the government is at this late stage seeing sense on this, as the DUP is detecting, then that is a huge breakthrough.

The 1985 Anglo Irish Agreement showed that the wishes of unionists in Northern Ireland can at any moment be cast aside. It is harder for to cast aside unionists in Scotland too.

Once again the Scottish Conservative leader Ruth Davidson is a voice of sanity. She first voted Remain, then argued for a mild Brexit, but a UK-wide one. Now she and her colleague, Scottish Secretary David Mundell, have promised to resign if NI has different Brexit arrangements to the rest of the UK.

“Having fought just four years ago to keep our country together, the integrity of our United Kingdom remains the single most important issue for us in these negotiations,” they said in a letter to Mrs May. They said they could not support a deal that creates a border of “any kind in the Irish Sea”. That includes regulations. Well said.