Theresa May has nine days to save her world

Theresa May (and I) are just back from Argentina. And she is about to enter the most important week of her political life and the most important week in this country’s political and constitutional history for decades.

It starts tomorrow with the publication of a summary of the legal advice on the PM’s Brexit plan - which will expose an irreconcilable contradiction at the heart of the so-called backstop to keep open the border on the island of Ireland.

On the one hand, if the UK were to trigger the backstop at the end of 2020, which would effectively take us into the EU’s customs union, the UK would never have the unilateral right to leave it. Our sovereign room for manoeuvre would be constrained in a fundamental way - which is precisely the opposite of what the Brexiters said Brexit would deliver.

On the other hand, it is unlawful - under the EU’s treaty - for this withdrawal provision negotiated under Article 50 to constitute the permanent economic relationship between the UK and EU.

So Theresa May argues that pragmatically the UK and EU have a common interest in terminating the backstop as fast as possible.

The problem for the Brexiters is first that they have heard and read from the EU that the backstop is an explicit “bridge” to the long-term trading relationship, so they fear that either it or something like it will be forever - which would make it impossible to do free trade deals with other countries.

As one said to me: “Remember when income tax was introduced in this country it was supposed to be temporary.”

The Tory Brexiters also want the PM to publish the full legal advice she received from the attorney general. So they are supportive of an initiative I revealed on Saturday by all the opposition parties, including Northern Ireland’s DUP - which is supposed to be the government’s partner but is increasingly behaving like a divorcing spouse - to urge the Speaker of the Commons to try to force publication, on the basis they say that MPs willed such publication a few weeks ago.

Officials tell me they will not buckle on this - because it would, they say, set a damaging precedent. Ministers will try to reassure estranged Tory MPs they will have all the material legal information they need.

The PM is facing defeat by a deal-eviscerating margin. Credit: AP

This fractious start to the week will set the tone on three eight-hour debates this week and two more next on what the Government deems to be the material elements in the Brexit plan.

Later today we may see precisely what will be debated on which days. The PM is being advised on this by the Chief Whip Julian Smith. He is telling her what her MPs need to be told that could turn opponents of her plan into supporters.

And then there is the question of when the PM herself will participate in the debate. Her colleagues say she knows she will have to play a leading role in it, and precisely when and how will probably be decided today.

Right now, she knows, she is staring not just at defeat when the vote on Brexit plan finally comes on December 11 but at defeat by a deal-eviscerating margin. As I said on Saturday, one of her colleagues says the margin of loss is looking like “nearly 400” (for the avoidance of doubt I don’t expect the majority against her to be anywhere near as great as that - but it shows how little faith her own team have that she can pull this off).

Theresa May has what in her terms are nine days to save her world - her Brexit, her party’s integrity, her job.