LONDON (AP) — The U.K.'s chief negotiator in post-Brexit trade talks called for "more realism" from the European Union before the start Tuesday of another round of discussions between the two sides.

With expectations of a breakthrough in the talks diminishing, there are concerns that they could collapse in the coming weeks. Though the U.K. left the bloc on Jan. 31, it is in a transition period that effectively sees it abide by EU rules until the end of this year. The two sides have been negotiating future trade ties over the past few months, but progress has been minimal.

David Frost, the British government's chief negotiator, said the two sides "can no longer afford to go over well-trodden ground" in the deadlocked talks and that the EU needs to show "more realism" about the U.K.'s status as an independent country. The EU side will be led by its long-time Brexit negotiator, Michel Barnier.

"We must make progress this week if we are to reach an agreement in time," Frost said. "We have now been talking for six months."

The trade discussions have made very little progress over the summer, with the two sides seemingly wide apart on several issues, notably on business regulations, the extent to which the U.K. can support certain industries and over the EU fishing fleet's access to British waters.

Relations appeared to become further strained Monday following reports that Britain's Conservative government was attempting to unilaterally ride roughshod over its divorce agreement with the EU that paved the way for the U.K.'s smooth departure earlier this year.

EU officials said any attempt to override the international treaty could jeopardize peace in Northern Ireland as well as undermine the chances of any trade deal.

The British government said the publication of planned legislation on Wednesday is intended to tie up some "loose ends" where there was a need for "legal certainty." It said the Internal Market Bill will ensure goods from Northern Ireland, which is part of the EU, will continue to have unfettered access to the U.K. market, while making clear EU state aid rules, which will continue to apply in Northern Ireland, won't apply in the rest of the U.K.

Though the government insists it's not planning to tear up its commitments, it appears that concerns over its intentions lie behind the resignation Tuesday of Jonathan Jones, one of the top officials in its legal department.

A spokesman for the Attorney General's office confirmed the resignation, but wouldn't comment on the reason behind it. The Financial Times reported that Jones quit because of a dispute over suggestions the government would challenge parts of the withdrawal agreement.

British Prime Minister Boris Johnson has said Britain could walk away from the talks within weeks and insists that a no-deal exit would be a "good outcome for the U.K." He said in a statement that any agreement must be sealed by an EU summit scheduled for Oct. 15.

British businesses are worried about a collapse in the talks that could see tariffs and other impediments slapped on trade with the EU at the start of next year. Most economists think that the costs of a "no-deal" outcome would fall disproportionately on the U.K.

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