Prime Minister Boris Johnson yesterday said that Britain and the European Union remain far apart, as he prepares to head to Brussels to try to salvage a post-Brexit trade deal. 

"I am always hopeful, but I have to be honest with you, the situation at the moment is tricky," he said, touring a hospital in London for Britain's historic rollout of a coronavirus vaccine.

"Our friends have to understand the UK has left the EU to exercise democratic control. We are a long way apart still," he said, ahead of face-to-face talks with EU commission chief Ursula von der Leyen.

"It is looking very difficult at the moment. We will do our level best. I would say to everybody there's great options ahead for our country."

After the negotiating teams' latest session in Brussels -- and with just over three weeks until Britain leaves the EU's single market -- Johnson held a phone call with von der Leyen late Monday and secured an invitation to head over in person.

"We agreed that the conditions for finalising an agreement are not there due to the remaining significant differences on three critical issues: level playing field, governance and fisheries," the pair said in a joint statement.

"We asked our chief negotiators and their teams to prepare an overview of the remaining differences to be discussed in a physical meeting in Brussels in the coming days."

It was not immediately clear whether Johnson's visit would be a separate event, or whether he might be slotted in before an EU summit tomorrow, with the other 27 EU leaders meeting in person.

The announcement of Johnson's trip came after a pessimistic day of talks, during which EU negotiator Michel Barnier told sceptical members of the European Parliament that Wednesday was the effective deadline for a solution ahead of the summit.

Barnier and UK counterpart David Frost were due to hold another session yesterday in Brussels.

In one olive branch, the UK government said it was ready to revoke clauses in Brexit legislation that have provoked legal action by the EU and undermined trust in London.

However, it kept the clauses intact as a "fall-back option" when the Internal Market Bill returned to debate in the House of Commons on Monday.

MPs voted to keep them in the text, rejecting a bid by the upper House of Lords to excise them.

Britain left the EU on January 31 and entered a transition period to allow negotiations to establish a trade relationship with zero tariffs and zero quotas.