If/when the UK leaves the EU in March 2019 as planned, Ireland will be the only country with a land border with the UK, and will be responsible for collecting EU customs duties on incoming goods.

EU spokespersons have said progress on resolving the border issue is a necessary precondition to discussing an EU-UK trade deal.

But representatives of Theresa May's UK government are taking the contrary line that moving Brexit talks along to discussions of a trade deal is a necessary precondition to further talks about the Irish border.

So - we have a Mexican - or Irish - standoff.

Who will blink first?

Watch this space.