The European Union's Brexit negotiator, Michel Barnier, said Monday sealing a new trade pact with Britain was still possible as negotiators sought to break deadlocks on access to UK fishing ­waters for EU vessels and corporate economic fair play rules.

Britain and the EU agreed on Sunday to "go the extra mile" in coming days to try to reach an elusive trade agreement despite missing their latest deadline to avert a turbulent split in trading ties at the end of the month.

"We are going to give every chance to this agreement... which is still possible," Barnier told journalists on arriving to update envoys from the 27 EU countries in Brussels on the UK talks. 

"Two conditions aren't met yet. Free and fair competition... and an agreement which guarantees reciprocal access to markets and waters. And it's on these points that we haven't found the right balance with the British. So we keep working." 

In London, British business secretary Alok Sharma said the estranged allies were still apart in Brexit trade talks but Prime Minister Boris Johnson did not want to walk away yet.

"We are of course apart on certain matters but... we don't want to walk away from these talks," Sharma told Sky. "People expect us, businesses expect us in the UK to go the extra mile and that's precisely what we're doing."

Johnson and the president of the EU's executive Commission, Ursula von der Leyen, had given negotiators a ­Sunday deadline to find a way to resolve an impasse on arrangements to guarantee Britain free trade access to the EU's single market of 450 million consumers.

On Sunday they mandated negotiators to continue, although Johnson sounded a downbeat note on prospects for a breakthrough.

Reports suggested the two sides were exploring a potential deal on how to respond if their regulations diverge over time and threaten fair competition.

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