London CNN  — 

The EU’s chief negotiator, Michel Barnier, has warned that the UK must abide by the terms of the Brexit deal it agreed last year, after reports that the British government was planning new legislation that would undermine elements of it.

The Financial Times, quoting three people familiar with the plans, reported that sections of a market bill slated for publication Wednesday, are expected to “eliminate the legal force of parts of the withdrawal agreement” in areas including state aid and Northern Ireland customs.

This “could undermine the agreement on Northern Ireland that Boris Johnson signed last October to avoid a return to a hard border in the region,” one person with knowledge of the plans told the FT.

The report has inflamed tensions between London and Brussels as post-Brexit trade negotiations enter their eighth round this week. “The withdrawal agreement has been signed and ratified by the UK and the EU, it is in force,” one EU diplomat told CNN, speaking on condition of anonymity. “If the UK chose not to respect it, then theoretically the EU would have to take legal measures,” the diplomat added.

In a statement on Twitter, Simon Coveney, the Irish foreign minister, said a move such as that described in the FT “would be a very unwise way to proceed” on Brexit.

The UK government did not dispute the FT story, although George Eustice, the UK’s environment secretary, suggested in an interview on Sky News that the story may have “exaggerated things.” He added that the “Northern Ireland protocol is agreed” and “part of the withdrawal agreement.”

A government spokesperson described the proposed legislation as a fallback position. The spokesperson said: “We are working hard to resolve outstanding issues with the Northern Ireland Protocol through the Joint Committee and will continue to approach these discussions in good faith. As a responsible government, we are considering fallback options in the event this is not achieved to ensure the communities of Northern Ireland are protected.”

Two Downing Street sources familiar with the government’s Brexit plans told CNN that they didn’t recognize large parts of the FT report. However, the news came on the same day Johnson warned that if a deal between London and Brussels was not concluded by October 15, when EU leaders are due to meet to discuss Brexit, then the UK would walk away from talks. “There is no sense in thinking about timelines that go beyond that point,” Johnson said in a statement. “If we can’t agree by then, then I do not see that there will be a free trade agreement between us, and we should both accept that and move on.”

There have been signs of tensions in the negotiating process in recent weeks. Brussels fears that the UK is trying to strike a deal on terms that mean it will not oblige the commitments it made to the EU in the Withdrawal Agreement. The UK thinks that Brussels is making demands on state aid and fishing that go way beyond those agreed last year and that the EU is refusing to accept that the UK is now an independent country.

Against that backdrop, it’s no surprise that the EU would balk at any suggestion the UK is planning to undermine the 2019 withdrawal agreement. “It’s interesting the leak appeared in the Financial Times, which has an international audience,” the EU diplomat said.

While the hardline rhetoric from Downing Street might concern officials in Brussels, some in London believe that Johnson is laying the ground for a major concession this autumn in order to secure a Brexit deal. A number of hardline Brexiteers told CNN last week that the best way through the current deadlock would be to repudiate parts of the withdrawal agreement.

Whatever the UK government’s true intentions, the latest developments have set nerves on edge in Brussels as the Brexit saga hurtles toward its final chapter.