Michel Barnier said it was a matter of “urgency” to agree the wording of a plan that would maintain the status quo on the Irish border, and gave no ground on the EU’s controversial demand that the backstop apply only to Northern Ireland.
His comments set the stage for the contentious Irish issue to remain at the centre of talks over the next six weeks, ahead of a summit of EU leaders in October that London continues to see as the deadline for a deal to be reached.
Mr Barnier was speaking following a six-hour round of face-to-face talks with the UK Brexit Secretary, Dominic Raab.
“We must have a detailed backstop solution which is legally binding in the Withdrawal Agreement,” Mr Barnier said. “Theresa May has committed herself to this, as have all the leaders of the EU institutions… it’s a matter of some urgency.”
The UK Government and politicians from across the spectrum have rejected the EU’s vision of a backstop that keeps Northern Ireland under European customs rules. That threatens to erect an internal trade barrier in the Irish Sea between Northern Ireland and the rest of the UK.
In a sign that the EU is not prepared to shift its stance, Mr Barnier said he had asked his UK counterpart for “a certain amount of data which is necessary for technical work… [on] how the necessary controls and checks take place”.
“The backstop is critical,” he insisted. “It’s essential to conclude negotiations because as I’ve said, without a backstop, there can be no agreement.”
"The solutions must be workable, they've got to be workable for the communities living in Northern Ireland and living in the Republic of Ireland."
Mr Barnier warned that a deal must be signed by "November at the latest". EU leaders will meet on 18 October, and while agreement on a withdrawal deal is no longer seen as likely by that data, Mr Raab said that he wanted to continue "accelerating and intensifying" negotiations.
"We're committed to resolving the deal by [October] and ultimately on my side I am stubbornly optimistic that a deal is within our reach."