The EU's chief Brexit negotiator Michel Barnier said he will return to London on Friday to pursue face-to-face trade talks, but warned that big differences remain.

Explaining that he was no longer self-isolating after a COVID-19 case on his team, Barnier confirmed he was returning to meet his British counterpart David Frost.

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.

In a tweet, Barnier warned that the "same significant divergences persist".

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.

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 Britain -- will suffer.

The talks have already pushed on much longer than expected and time is running out for ratification of any agreed deal by the European Parliament by the end of the year.