Michel Barnier has delivered a firm rebuff to Boris Johnson over claims that it would be “undemocratic” for Brussels to expect the UK to sign up to a “level playing field” on rules and regulations in a future trade deal.

The claim was made in a high-profile speech last night by the prime minister’s chief Brexit negotiator David Frost, who said that the ability for Britain to diverge from EU rules was the main point of withdrawal.

But Mr Barnier said that agreement on common rules in areas like workplace rights and environmental protections was necessary to avoid unfair competitive advantages between businesses on opposite sides of the Channel. Brussels fears that the absence of shared regulations would result in the UK “dumping” cut-price goods produced to lower standards in its markets.

He pointedly noted that Mr Johnson himself signed up to “robust” level playing field arrangements in the political declaration agreed with Brussels only a few months ago.

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And he cast doubt on the prospect of the UK securing the Canada-style trade deal which the PM is seeking without a commitment of this kind, insisting that Britain’s geographical proximity to the remaining 27-nation bloc meant the two countries’ positions were not comparable.

In a signal that Brussels is not ready to budge on the position agreed with the UK in October, Mr Barnier said: “We remain ready to work very quickly with the UK on the basis of the political declaration agreed with Boris Johnson just a few months ago. We remain ready to propose a partnership if the UK want it.”

The impasse points towards a strictly limited trade deal - or no deal at all - when the transition period to Brexit ends in December, raising the prospect of tariffs and non-tariff barriers on UK exports to the continent.

Speaking in Brussels on Monday, Mr Frost said that the UK was “not frightened” by the threat of greater trade friction.“

The ability for the UK to set its own rules “isn’t a simple negotiating position which might move under pressure,” said Mr Frost. “It is the point of the whole project.”

Any attempt to force Britain to comply with Brussels regulations would be “unsustainable”, he argued, adding: “At some point democratic consent would snap – dramatically and finally.”

But Mr Barnier said that the level playing field demand was “truly not” undemocratic.

“It is a sovereign decision of the UK and the EU to put in certain subjects their rules, their norms in co-operation with each other,” he told reporters in Brussels.

“It is a sovereign decision of the EU, it is a sovereign decision of the UK to co-operate.”

The chief EU negotiator pointed to last October’s political declaration document, in which Mr Johnson agreed to pursue a future relationship ensuring “open and fair competition, encompassing robust commitments to ensure a level playing field”.

“It is formally written in the political declaration to prevent that distortion of competition, unfair competitive advantages,” said Barnier.

“That is what Boris Johnson wrote in the political declaration. I am looking for a means calmly and seriously to translate into legal form the political commitments made with the UK - with the UK, not without it.”