Britain's Prime Minister Boris Johnson declared himself disappointed in the progress of post-Brexit trade talks Wednesday, but he will wait for news from an EU summit before deciding whether to pull the plug.

During a cross-Channel call on the eve of the crunch talks, EU chief Ursula von der Leyen warned that there was "still a lot of work ahead of us" and that Brussels wanted a deal -- just "not at any price."

A Downing Street spokesman said that Johnson, talking to von der Leyen and EU summit host Charles Michel, had "expressed his disappointment that more progress had not been made over the past two weeks."

The British leader had warned last month that he would walk away from the table if there was no deal in sight by October 15, but his spokesman said he would now wait for the 27 EU leaders to meet on Thursday and Friday.

"The Prime Minister said that he looked forward to hearing the outcome of the European Council and would reflect before setting out the UK's next steps," the spokesman said.

Britain's Prime Minister Boris Johnson (L) and European Commission President Ursula von der Leyen, seen here earlier this year, are to hold new post-Brexit talks
Britain's Prime Minister Boris Johnson (L) and European Commission President Ursula von der Leyen, seen here earlier this year, are to hold new post-Brexit talks AFP / Tolga AKMEN

The British side has accused Brussels of trying to force concessions by running down the clock, with the window narrowing on chances to agree and ratify a deal before the UK leaves the EU single market on December 31.

But von der Leyen stressed that the two sides were still far apart on the EU member states' three priorities in the talks. "Conditions must be right, on fisheries, level-playing field and governance," she said.

European diplomats say Brussels is still hoping for a deal, but is looking for a sign from Johnson that he is serious about compromise.

"We need to lower the landing gear. We're approaching the runway. Is he thinking about landing or is he still at 10,000 metres?" one asked.

According to draft summit conclusions seen by AFP, but likely to evolve ahead of the summit, the EU will express concern "that progress on key issues of interest to the Union is still not sufficient for an agreement to be reached."

They will invite EU negotiator Michel Barnier to "intensify negotiations" to strike and implement a trade deal before January 1.

Key events in the Brexit process
Key events in the Brexit process AFP / Gillian HANDYSIDE

Diplomats said there had been some movement from Britain on the rules of fair trade in recent days, but not enough to warrant locking the negotiators into a so-called "diplomatic tunnel" to force the talks over the finish line.

Some member states are pushing for the sides to an agree on a "toolbox" of retaliatory measures that Brussels could take if it feels that Britain has broken its word on maintaining a level-playing field in cross-Channel business.

Britain left the European Union on January 31, but Barnier and UK negotiator David Frost have been locked in inconclusive talks on a follow-on arrangement for cross-Channel business.

If no deal is reached, trade rules will revert to the bare bones of World Trade Organisation regulations.

Both sides insist they are ready for this -- and would prefer it to having to accept a deal that oversteps their red lines -- but experts forecast severe economic disruption.

Europe's three main concerns are agreeing on the rules of fair competition, agreeing how these rules will be policed and securing access to UK waters for EU fishing fleets.

Britain wants to reassert sovereignty over its waters and refuse EU legal oversight over the deal -- insisting it wants a simple trade deal of the kind the EU signed with Canada.

Brussels in turn stresses that Britain's economy is far more integrated with and closer to the EU's than Canada, and that its single market must be protected from British backsliding.

Northern fishing nations, in particular France, are holding a firm line on fishing, insisting that their boats operated in UK waters for centuries before the EU was formed.