BRUSSELS: British and European negotiators were sent back to work Sunday after Prime Minister Boris Johnson and EU chief Ursula von der Leyen agreed to abandon their supposed make-or-break deadline.

The pair had said last week they would decide whether an agreement was possible by the end of Sunday, but after a cross-Channel crisis call they agreed to “go the extra mile.”

“We had a useful phone call this morning. We discussed the major unresolved topics,” von der Leyen said in a video message, reading out a joint statement agreed with Johnson.

“Our negotiating teams have been working day and night over recent days.”

The EU’s Michel Barnier and Britain’s David Frost held talks late on Saturday and early on Sunday. They have been alternating between the capitals but a European official said that, for the moment, they would remain in Brussels.

In their joint statement, the leaders said: “We have accordingly mandated our negotiators to continue the talks and to see whether an agreement can even at this late stage be reached.”

But speaking for himself, Johnson insisted that agreement was far from sure with less than three weeks to go until Britain leaves the EU single market at the end of the year.

“I’m afraid we’re still very far apart on some key things, but where there’s life there’s hope,” he told reporters.

“The UK certainly won’t be walking away from the talks. I still think there’s a deal to be done if our partners want to do it,” he added, four days after he and von der Leyen had said they would pull the plug on talks on Sunday if no breakthrough was in sight.

Johnson said Britain “would be as creative as we possibly can” — amid reports that the sides are nearing a deal on how to respond if their regulations diverge over time and threaten fair competition.

But Britain could not compromise on the “fundamental nature” of Brexit, controlling UK laws and fisheries, he said.

Without a trade deal, cross-Channel trade will revert to WTO rules, with tariffs driving up prices and generating paperwork for importers, and the failed negotiation could poison relations between London and Brussels for years to come.

Ireland stands to lose out more than most EU countries if trade with its larger neighbor is disrupted, and Foreign Minister Simon Coveney cautiously welcomed the reprieve for negotiations.

“Time to hold our nerve and allow the negotiators to inch progress forward, even at this late stage. Joint statement on Brexit negotiations is a good signal. A deal clearly very difficult, but possible,” he tweeted.