Brexit Secretary David Davis has criticised the "discourteous" European Union for publishing plans that would leave the UK facing possible sanctions during a transition period.
Turning up the heat as a week of technical negotiations on the transition came to a close, Davis said he regarded the Brussels documents as "political" and "unwise."
His comments came after Theresa May's Brexit inner "war cabinet" met over two days to consider the next stages of the process.
Today (February 9) the senior officials involved in the Brexit talks will meet in Brussels where the EU expects key Brexit adviser Olly Robbins to provide an update on the UK's plans.
But in a fresh sign of tension, Davis accused the EU of not acting "in good faith" over the proposed transition deal to cover a period of around two years after the UK leaves the bloc in March 2019.
The EU has released a position paper showing it wants to put in place a method to rapidly curtail the UK's single market benefits if it breaches the terms of a transition deal.
Davis said: "I do not think it was in good faith to publish a document with frankly discourteous language and actually implying that they could arbitrarily terminate, in effect, the implementation period.
"That's not what the aim of this exercise is, it's not in good faith, and we think it was unwise to publish that."
Under the plans released by the European Commission, Brussels wants to be able to "suspend certain benefits" of the internal market for the UK without going through the lengthy European Court of Justice (ECJ) legal process.
Meanwhile, Japanese investors, including representatives from car giants Nissan, Honda and Toyota, gathered for a meeting at Downing Street and made clear that they expected access to the single market to continue after Brexit.
Japan's ambassador to the UK Koji Tsuruoka said there were "high stakes" and firms would not be able to continue operating unless they could remain profitable.
May told the gathering that Brexit was "no small undertaking" but presents an opportunity to "strike free trade deals around the world and build on our already strong relationship with Japan."
Downing Street said there was agreement at the meeting on "moving quickly in the negotiations to secure a trading relationship with the EU that is as tariff-free and frictionless as possible following the implementation period."