Significant differences remain in talks over a trade deal between Britain and the European Union, both sides said on Saturday, as they promised to step up efforts to find an agreement.

After a call between British Prime Minister Boris Johnson and European Commission President Ursula von der Leyen, both said talks would continue in London next week but that the main sticking points remained.

"The prime minister set out that, while some progress had been made in recent discussions, significant differences remain in a number of areas, including the so-called level playing field and fish," a spokesman for Johnson's office said.

There was a similar message from Von der Leyen. "Some progress has been made, but large differences remain especially on level playing field and fisheries," she said on Twitter.

Johnson said negotiators would "redouble efforts to reach a deal".

"Our teams will continue working hard next week. We will remain in close contact in the next days," Von der Leyen said.

Britain formally left the EU last January but has been following the bloc's rules since then as the two sides try to agree on their future trade relationship.

Both leaders said they had agreed to remain in personal contact as well, signaling a stepped-up political effort to secure a new trading partnership before Britain ends a post-Brexit transition period on December 31.

Before then, several weeks are needed for any treaty to be vetted and ratified by both sides, and observers have said they will be cutting it very fine if an agreement is not reached by mid-November.

(With input from Reuters, AFP)