Negotiators for the EU and Britain are hoping for a breakthrough in trade talks this week, despite feuding over a controversial UK bill that threatens to scupper a post-Brexit deal.

Scores of officials planned to assemble in Brussels from Monday in efforts to forge a compromise on negotiating positions that have not budged on key areas since the talks on future relations began six months ago.

Both London and Brussels say a deal on a free trade agreement must be struck by mid-October to allow time for it to be ratified before coming into force from January 1 next year.

Failure to do so would see trade conducted on World Trade Organization rules, with higher tariffs and quotas and almost certain economic chaos for Britain and Europe.

Chief negotiators Michel Barnier and the UK's David Frost met last week to prepare the round of talks, in meetings that London characterized as "constructive."

European diplomats remained cautious that a breakthrough was possible, seeing this round of meetings as laying the necessary groundwork for a final push later in October.

"Next week, a path to a deal should be identified," an EU source said. "If we have zero movement, the process will be in big trouble."

EU capitals were incensed by Johnson's decision to push an Internal Markets Bill in his own parliament that his own government admits would break international law by overwriting the withdrawal treaty.

Brussels intends to launch legal action against the measure, but decided to continue talks on a trade deal as the bill passes through the Commons and House of Lords.