FOR a draft treaty 188 pages long, the key sentence on how the European Commission proposes to solve the Northern Ireland border problem is remarkably straightforward: “A common regulatory area comprising the Union and the United Kingdom in respect of Northern Ireland is hereby established.” The draft also suggests, provocatively, that Northern Ireland would become part of the EU custom’s territory i.e. part of the customs union, implying a border in the Irish Sea.

Cue declarations of the inviolable constitutional integrity of the UK from Theresa May and dire warnings from the DUP. But what did Mrs May think “full alignment” of regulations meant in the joint EU-UK agreement she signed in December?

The Commission’s draft treaty tries to put that agreement into legal form. In the absence of detailed proposals from the UK, this is Brussels’ interpretation (backed by Irish government).

Crucially, the EU also said at its December summit that without progress on this legal version, transition and trade talks may not move forward. The EU’s chief negotiator Michel Barnier declared he was not trying to provoke but that with only 13 months to go until Brexit day the time for speeches was past. Successful negotiations, Mr Barnier said, need to focus on the text of the future inter- national withdrawal agreement between the UK and EU.

This marks the moment of the end of any phoney war in the Brexit talks. Mr Barnier earlier in the week also expressed his frustration at the lack of progress on resolving disagreements on transition – suggesting, sharply, that David Davis should be in Brussels sorting this out with him.

Mrs May will tomorrow say what sort of future relationship the UK wants with the EU, but is likely to set out a “managed regulatory divergence” approach that has already been dismissed byEU president Donald Tusk as illusory and by Mr Barnier as cherry-picking.

With Jeremy Corbyn finally creating a distinction between Labour and Tory policies in his backing of a customs union, and with Welsh and Scottish governments bringing in continuity bills, there is huge stress on Mrs May’s government.

The politics of Brexit have looked like imploding for a long time: they are certainly starting to topple.

Kirsty Hughes is director of the Scottish Centre On European Relations.