EU chief Ursula von der Leyen warned Wednesday that any post-Brexit trade deal must not undermine the EU single market, as frustration with London grows.

The UK leaves Europe's trade and customs area in five weeks, but talks on a follow-on agreement are still stalled over fishing rights and fair trade rules.

Europe's chief negotiator Michel Barnier is in self-isolation in Brussels until Thursday, after a member of his team tested positive for coronavirus.

But EU officials could not say when he would return to London for face-to-face talks with UK counterpart David Frost, and diplomats said they want to see a sign Prime Minister Boris Johnson is ready to compromise.

"We will do all in our power to reach an agreement, we're ready to be creative," von der Leyen, president of the commission, she told the European Parliament, warning that Britain must agree to fair trade rules.

"But we are not ready to put into question the integrity of the single market, the main safeguard for European prosperity and wealth."

And she repeated Brussels' warning that Britain would not enjoy the benefits of EU membership from the outside: "There will be a clear difference between being a full member of the union and being just a valued partner."

She acknowledged MEPs' frustration that time was running out for them to debate and ratify any trade deal before Britain leaves the single market on January 1.

But she warned that Johnson's tactics had shown the need for clear rules.

"We want to know what remedies are available in case one side will deviate in the future because trust is good, but law is better," she said.

London has been resisting signing up to the EU's vision of a post-Brexit "level playing field", with trade penalties if either side diverges from agreed standards.

Johnson has also introduced a draft law to govern the UK internal market that his own government admits would breach promises made in Britain's EU withdrawal treaty.

This has undermined Brussels' trust in Britain, and talks have now blown past several unofficial deadlines, leaving only a narrow window for agreement before the end of the year.

European Commission vice-president Maros Sefkovic said he hoped to hold a meeting with British minister Michael Gove and their joint committee on implementing the withdrawal deal in the coming days.

European Commission President Ursula Von Der Leyen
European Commission President Ursula Von Der Leyen restated the EU position in Brexit talks, but in sterner than usual terms Photo: POOL / Olivier HOSLET

But it was not clear when Barnier would resume the cross-Channel shuttle diplomacy and resume face-to-face talks.

Brussels is keen to see movement from London in implementing border controls between Great Britain and Northern Ireland, which will remain in the EU single market despite being a part of the UK.

"Barnier should really think hard about going back because right now it doesn't seem worth it," one European diplomat said, saying of London: "They haven't made up their mind if they want a deal."

A UK government spokesman said: "Talks continue remotely this week. We expect them to resume in London in person as soon as it is deemed safe to do so, as we had previously agreed with the EU."

If a deal cannot be signed and ratified by December 31, cross-Channel trade will face a tariff barrier and businesses on both sides -- but especially, experts agree, in Britain -- will suffer.

The main areas of disagreement remain fishing rights, the level-playing field and the powers of the overall governance mechanism of the eventual accord.

In Westminster, Johnson told the UK parliament: "Our position on fish hasn't changed, we'll only be able to make progress if the EU accepts the reality that we must be able to control access to our waters."

But in Brussels, the EU parliament is determined not to be bumped into last minute concessions.

"We cannot just simply agree to anything that comes up in the last minute. This parliament needs time for scrutiny," said German MEP Ska Keller, a leading member of the Greens group.

Von der Leyen re-stated the EU position -- but in sterner than usual terms -- reflecting the mounting concern among her parliamentary audience that time has run out.

"No one questions the UK's sovereignty in its own waters. But we ask for predictability and guarantees for fishermen and fisherwomen, who have been sailing in these waters for decades, if not centuries," she said.

"Honourable members, as I said, the next days are going to be decisive. The European Union is well prepared for a no deal scenario. But of course we prefer to have an agreement."

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