Theresa May has strung herself and her government up on a DUP hook from which there is apparently no escaping. Short, that is, of telling the unionists she has no choice but to make a commitment to the possibility of customs controls on the Irish Sea to secure the greater objective of a frictionless border between North and South.

Last week she was told by the EU in Brexit talks in no uncertain terms that her complex formula for sidestepping the “backstop” commitment she made in December – or, rather, reinterpreting it - is a complete non-runner.

She must now go back to the drawing board and produce a new way of operationalising the backstop that reflects the uncomfortable promises made in December. This backstop ensures no divergence in customs and trade rules between the Republic and Northern Ireland in the event there is no agreed solutions on how to avoid a hard border. And she must do so fast as a June summit is looming.

How she ever thought it would be a runner is not clear, as one senior EU official close to the talks admitted. “You are not the only one to be confused here,” he told this correspondent at a post-talks briefing.

Special protocol Mrs May has struggled with the reality that in December, in order to demonstrate “sufficient progress” and see talks move on to their next stage, the backstop commitment was conceded as a guaranteed fallback to the EU for the Withdrawal Agreement in case longer-term talks failed to produce a borderless EU-UK trade deal. It is now enshrined in draft, unagreed form in a special protocol to the Withdrawal Agreement.

And May has been suggesting in recent weeks that the customs provisions suggested in the backstop should be extended on a UK-wide basis to obviate the need for any separate treatment of Northern Ireland goods. This would be on a strictly time-limited basis, she insisted, so that the UK’s ambitions to sign separate trade deals would not be unduly inhibited.

Two problems: the time limit undoes the guarantee element of the backstop; and the UK was only committing to the customs element of the backstop, not its full regulatory alignment. Absent the latter there can be no frictionless Border.

Future relationship The UK had refused to discuss the backstop issue in the Ireland talks strand last week, but, to the surprise of EU negotiators, sought to raise it in the “future relationship” discussions in another room. “We have not addressed these issues in the context in which they need to be addressed,” the EU official complained.

“They did, however, in the beginning of the meeting on the future partnership,” he said, “refer to the fact that Mrs May remains determined to address the Irish Border issue through the overall EU-UK relationship.

“They said that they are currently discussing only the customs dimension of the backstop and that they are looking at making that EU-UK-wide. At the same time they said that they recognise that the Article 50 agreement (Withdrawal Agreement) protocol could not set out the permanent long-term EU-UK customs relationship.”

Still confused?

So was the official, he confessed. Progress can’t be made to the June “sufficient progress” talks yardstick unless, he insisted, “we have a recognition that the backstop has to be Northern Ireland-specific. And we do away with the fantasy that there is an all-UK solution to that.

“And we need to have the recognition that regulatory alignment for Northern Ireland is the key to avoiding a border. “Progress at this stage seems elusive – substantive progress even more so.”

Uncomfortable call The EU now awaits, within two weeks at most, an explanation in writing of how the agreed backstop will be operationalised and the legal language for it for the Withdrawal Agreement. Arlene Foster can expect an uncomfortable call from Downing Street.