An electronic advert alerts businesses that they need to be ready for the end of the "Brexit transition period" is pictured in a bus stop in London on Wednesday. Photo: AFP

UK Prime Minister Boris Johnson was Brussels-bound on Wednesday, with Britain's fading hopes for a post-Brexit trade deal hanging on crisis talks with EU chief Ursula von der Leyen.

Johnson's dash back to the city where once he made his name as an EU-bashing newspaper reporter marks the last chance of a breakthrough before Britain leaves the EU single market.

Talks are blocked over the issue of fair competition, with Britain refusing to accept a mechanism to allow the EU to retaliate swiftly if the UK business regulations change in ways that put European firms at a disadvantage.

EU negotiator Michel Barnier and his UK counterpart David Frost have narrowed the gaps over eight months of talks, but London insists it will reclaim full sovereignty at the end of 2020.

If Britain leaves the EU single market in three weeks without a follow-on trade deal the delays that travelers and freight will face at its borders with the EU will be compounded by import tariffs that will drive up prices.

Johnson spoke to Von der Leyen on Monday by telephone to secure the last chance dinner invitation after Barnier and Frost's negotiations broke off without agreement.

He was expected to travel by plane and arrive late Wednesday for talks at the Berlaymont building, the EU headquarters he once wrongly reported was slated for demolition when he covered Brussels as a newspaper journalist in the early 1990s. But officials on both sides expressed pessimism ahead of the last-ditch encounter.

"I am always hopeful, but I have to be honest with you, the situation at the moment is tricky," Johnson said as he toured a London hospital on Tuesday.

Barnier, meanwhile, gave a downbeat briefing to European ministers ahead of Thursday's EU leaders summit, then tweeted: "We will never sacrifice our future for the present. Access to our market comes with conditions."

AFP