Never mind the practicalities, look at the politics. The UK Tariff plan – and its timing - is designed to pressure the Irish into abandoning the backstop at next week’s European Council, to give Theresa May the opportunity to bring the rest of the Withdrawal Agreement back to Westminster for another "meaningful vote".

This tariff plan was supposed to be published last week, but was delayed until today to give the UK government new leverage and energy in the run into the summit.

Q&A: What is a tariff?

Today’s meeting of EU Ambassadors, or Permanent Representatives, could be uncomfortable if you are Irish. It will be the first test of whether the EU united front is cracking as we head towards the cliff edge. That will certainly be the hope of the British side, who don’t want to leave the EU in a disorderly, no-deal fashion, but who cannot get the deal past a parliament that objects to the backstop element.

So the EU now faces a renewed choice – protect a vulnerable member state or protect the wider economic and political interest of securing UK departure with a deal (something the vulnerable state also has a massive interest in securing).

Publishing a tariff and Northern Ireland border plan now, rather than weeks or months ago, exerts maximum pressure on the Irish Government at a time when most of its members are scattered to the four corners of the globe – promoting Irish interests through the St Patrick’s Day brand – leaving little time for face-to-face huddles or hand holding of sectoral interest groups.

Given the high level of preparedness shown by the Irish Government throughout this Brexit process, it’s not unreasonable to assume they have war-gamed such a British tactic and already have a plan to deal with it. But it’s still going to be a sweaty, uncomfortable time to be an Irish minster or diplomat.

The tariff and border plan itself has more holes than a fishing net and is being pulled apart by trade experts. But it will probably have the desired political effect of causing the sectoral groups – particularly the always vulnerable farming and agri-business sector - to scream in pain, upping the panic factor in Irish politics (which is structurally super-attentive to constituents’ needs, sometimes to the disadvantage of the bigger picture).

More important will be how the other 26 governments decide to play it. Will they start asking the Irish to "be reasonable, for all our sake"?

Shortly after 9am, Michel Barnier addressed the European Parliament. There was no indication from him of any sliding away from a commitment to Ireland.

He identified the maintenance of peace on the island of Ireland as his first priority in the process. He stressed that all UK politicians who want to exit the EU in an orderly fashion with a deal have to take the deal that has been on the table since last November.

Mr Barnier also repeated Jean-Claude Juncker’s assertion that there would be no more negotiations – because they cannot go any further.

That’s right. The commission has run to the limit of its negotiating mandate. Only a higher forum can change the mandate, and that is the European Council, meeting in Article 50 formation (i.e. without the British) – and that is happening next Thursday week, late afternoon.