There are some things that have to be taken as given in life. Right now Theresa May would be wise to assume that amongst the list of givens are:

The EU not changing its conditions for trade talks to commence;

Ireland not changing its demands;

The DUP not changing its position;

The hard-Brexiteers not going soft.

This then means:

There can be no Irish border for customs purposes;

Northern Ireland cannot have rules distinct from the U.K. (except when it suits the DUP to do so);

There can be no border in the Irish Sea;

There can also be no border at Calais or elsewhere - because what happens on the Irish border has to also happen elsewhere, because that is how common markets work.

In effect May conceded all of this on Monday. Or she did so if she wants talks to continue, and I have no doubt she does.

So, if that’s the case there is only one party left in the negotiation that can change its mind. And that is the UK.

And there is only one thing the UK can change its mind on. And that is the customs union. I stress the Single Market is not an issue as yet: that is what the next round of talks is about. Right now we’re simply discussing border controls. And borders without controls - which have to happen now or progress ends - mean a customs union. And the EU has one. And it is not going to create a new one for the UK. Add that to the list of givens, if you like.

So Theresa May has a simple decision to make. It’s take it or leave it time for her on the customs union. She previously, and without good reason, said no to it. Or rather, she did so to appease the Tory hard-right who think there is a better customs union in the rest of the world although there is not a shred of evidence that this is true.

So Theresa May has an implicit second decision to make. Does she keep the EU, Ireland, the DUP, most UK businesses, most UK people and most of the House of Commons on side, or does she appease Jacob Rees Mogg?

There is, of course, only one viable answer here. And if Tory civil war breaks out, so be it. As I have said before, she must show the courage Michael Collins displayed in Ireland in 1922, and do what is best for the country. Collins paid with his life. I sincerely hope May only loses nothing more than her relationship with some in her own party with whom she has never been much in sympathy. She could not lose credibility: that departed long ago.

But will she do what is required? I do not know. I am not sure she can decide. You can only seek high office if you want to make decisions, and she appears wholly unable to undertake this most basic task of her job.

So we are still left with some givens. May can:

Decide to stay in the customs union, and alienate her party but keep talks going;

Decide to leave the customs union and fail the DUP and see her government fall as an Irish border will happen;

Prevaricate, which amounts to the second option in practice.

It’s either / or time then. And I am still not sure she has a clue as to what to do.