Shadow Brexit Secretary Sir Keir Starmer brushed aside Downing Street’s claims that the face-to-face with the EU Commission’s President was “constructive” and said the leaks proved Ms May had misjudged her hand in negotiations.
Sir Keir’s words were echoed by the SNP and Liberal Democrats, whose leader Tim Farron said the furore had blown “a massive hole” in Tory arguments for Brexit – and accused the PM of “astonishing arrogance”.
According to the Frankfurter Allgemeine newspaper's report, EU officials and Mr Juncker were surprised Ms May did not appear to be fully briefed for the meeting last week, claiming she had unrealistic expectations.
Sir Keir said: “This is a deeply worrying account and further evidence that Theresa May’s rigid and complacent approach to Brexit negotiations risks leading Britain over a cliff edge.
He added: “[She] talks about strengthening her hand, but in reality she has misjudged her hand at every turn, weakening Britain’s position.
“By refusing to acknowledge the complexity and magnitude of the task ahead the Prime Minister increases the risk that there will be no deal, which is the worst of all possible outcomes.”
Ms May responded on Monday by dismissing the reports as “Brussels gossip” and repeating the line that the talks had been “constructive”.
According to the German paper, Ms May told EU officials she expected to be elected Prime Minister next month and wanted to “make Brexit a success”, but was told that would be difficult because the UK would be worse off in the future as a “third country” outside of the EU.
The PM was also reported to have said that she wanted to deal with Brexit talks in four-day blocks every month, and keep discussions confidential, but Mr Juncker apparently pulled two piles of paper from his bag - Croatia’s EU entry deal and Canada’s free trade deal - highlighting how complex these talks would be.
There was a clash over the Brexit ‘divorce bill’ with Ms May insisting there was nothing in the treaties saying the UK should pay. The Prime Minister was also said to have told the EU officials she wanted to clarify the rights of UK citizens in Europe at the EU Council in June, but the idea was dismissed by Mr Juncker as too soon for something so complex.
The morning after the Wednesday meeting, Mr Juncker called German Chancellor Angela Merkel and reportedly said Ms May “lived in another galaxy” and was “deluding herself”.
A Government spokesman said: “We do not recognise this account.
“As the Prime Minister and Jean-Claude Juncker made clear, this was a constructive meeting ahead of the negotiations formally getting underway.”
Lib Dem leader Tim Farron said he is “clear this Government has no clue and is taking the country towards a disastrous hard Brexit.”
He added: “Theresa May chose a divisive hard Brexit, with Labour's help, and now has no idea what to do next.
“This election offers us a chance to change the direction of our country, keep Britain in the single market and give the people the final say over what happens next.”
Scotland’s Minister for UK Negotiations with the European Union Michael Russell said the account of the meeting had been “devastating”.
He added: “[It] lays bare the reality of the Tory Government’s weak and chaotic leadership of Brexit – having seen first-hand how the Tories negotiate on EU matters, I am frankly not surprised by anything reported here.
“Behind the façade and the robotic sound-bites the Tories are quite clearly not being straight with people about their plans for Brexit.”