Theresa May’s Brexit plan was left mired in uncertainty after reports that the EU’s chief negotiator, Michel Barnier, told British MPs that “les propositions sont mortes” in a Brussels meeting.

The Labour MP Stephen Kinnock revealed that in talks this week Barnier had declared the Chequers proposals “dead” and suggested that there was a fundamental misunderstanding in the UK about how the single market worked.

“I can tell you absolutely, unequivocally, without a shadow of a doubt that Chequers is dead in the water. Michel Barnier made it crystal clear that Chequers is completely unacceptable to the EU,” Kinnock said.

The senior remainer urged the Brexit secretary, Dominic Raab, and the prime minister’s Brexit adviser Olly Robbins, appearing before the European scrutiny committee on Wednesday, to accept that Brussels was not simply “sabre rattling” as a negotiating tactic.

May faces a concerted campaign to “chuck Chequers” from disgruntled Tory MPs, led by the former ministers Boris Johnson and David Davis. There are also deep-rooted concerns in Brussels over her facilitated customs arrangement and common rulebook proposals.

Bill Cash, the veteran Tory Eurosceptic, told the committee that Chequersshould be “put out of its misery” as the plan satisfied “virtually no one” while the former Brexit minister David Jones asked why the government was “flogging this dead horse”.

However, Stefaan de Rynck, a senior adviser to Barnier, threw the government a lifeline when he cast doubt on Wednesday night over the claims that Brussels thought Chequers was a total non-starter, though he did not deny there were problems.

He tweeted: “Michel Barnier actually said in no uncertain terms that Chequers has positive elements, w/ reference to security & foreign policy and to an FTA as a common denominator for the economic partnership after Brexit.”

Facing the committee, Raab suggested British MPs had been “used as a pressure exercise” by Brussels as part of their negotiating tactics.

“This is a negotiation with the EU so you are going to hear noises from various sides that are critical. That is an inherent part of a sensitive, contentious negotiation like this, but you should be in no doubt that we are making good progress,” he said.

He dismissed calls by Brexiters to instead pursue an enhanced Canada-style free trade agreement, which Barnier has previously raised as an alternative, as it risked splitting Northern Ireland from the rest of the UK.

Robbins added that the UK government respectfully disagreed with Barnier’s alleged comments and it maintained its view that the Chequers proposal was a “credible, sensible” balance between respecting EU autonomy and UK sovereignty.

He raised the hackles of Brexiters by hinting that he had shared elements of the plan with the EU before it was presented to the cabinet. He suggested it was his responsibility to keep ministers informed of the other side’s views.

At prime minister’s questions Jeremy Corbyn mocked the prime minister’s dancing on her Africa trip last week, warning her she could not “keep dancing round all the issues” on Brexit. “The Chequers proposal is dead, already ripped apart by her own MPs. When will the prime minster publish a real plan that survives contact with her cabinet and reality and protects jobs?” he said.

May, meanwhile, directly challenged the Labour leader to rule out a second Brexit referendum, but he sidestepped the calls.

Rees-Mogg: Barnier agrees that Chequers proposal is 'rubbish' Read more

The dispute over the Chequers plan followed claims, first reported by the Guardian, that Germany was ready to accept a less detailed political declaration on the future as the best way to avoid a no-deal Brexit, thus postponing some of the most contentious trade issues until after Brexit.

This could take the form of a 10-page document, when negotiators on both sides were once planning a document of up to 100 pages.

However, the French president, Emmanuel Macron, has stressed his opposition to a “blind Brexit” in which the UK leaves the EU without clarity on the terms of a future deal, fearing that it could lead to an extension of the 21-month transition period.

Downing Street has also poured cold water on the idea. A senior No 10 source said: “We would have a big problem with a fudge on this. Some in the EU seem to think we could just have an expression of general intent, but that won’t wash with MPs. We need to get it through the Commons so we need as much detail as possible.”

Jacob Rees-Mogg, chair of the pro-Brexit European Research Group, said: "I think it would be very difficult for the government to get parliament to vote for a £40bn payment without clarity about what is being received in return.” He added that a 10-page document would represent £4bn a page.

Another senior leaver said that if the prime minister sought to fall back on a blind Brexit it would suggest she was backing away from Chequers – and opponents would rather press home their advantage and force her to drop it altogether, than allow the issue to be fudged.