Juncker questions "stability and accountability" of Davis and his political mandate to conduct Brexit talks

An official Commission spokeswoman declined to comment on the minutes, saying the situation had "moved on" since July 12, when Mr Barnier briefed Mr Juncker and other commissioners.

Mr Juncker's comments emerged as Mr Barnier released a raft of new papers setting out the EU's negotiating position on sensitive issues including the future of the Irish border, customs arrangements, intellectual property rights, public procurement and data protection.

They also came as MPs began a bruising House of Commons showdown over the Government's key Brexit legislation, with Labour threatening to vote down the EU Withdrawal Bill, which repeals Britain's EU membership and with other parties tabling amendments to block it.

The minutes of the July 12 meeting at the Commission's Berlaymont HQ recorded that Mr Juncker "expressed his concern about the question of the stability and accountability of the UK negotiator and his apparent lack of involvement, which risked jeopardising the success of the negotiations".

In an apparent reference to the Conservative Government's loss of its overall majority in the June General Election, the minutes added that Mr Juncker urged Mr Barnier "not to accept discussions at the purely technical level with negotiators who had no political mandate, while fundamental political questions still remained".

The official minutes came as new papers from Brussels made clear the Commission puts the responsibility for sorting out arrangements for the Irish border after Brexit solely on Theresa May’s Government

The latest batch in a series of documents setting out the EU's negotiating position are due today but do "not put forward solutions" for resolving travel between the north and south of the island of Ireland after 2019.

Instead the papers say the onus to sort out the problem "remains on the UK".

"The present paper does not put forward solutions for the Irish border," the papers state.

"The onus to propose solutions which overcame the challenges created on the island of Ireland by the UK's withdrawal and its decision to leave the customs union and the internal market remains on the UK."

Mr Davis has insisted discussions with Brussels on border plans have been "good" but Mr Barnier made clear "a lot more substantial work" needed to be done.

The EU paper calls for "unique solutions" and floats the possibility of "specific provisions" being included in the exit agreement to address the fact the peace process was underpinned by common EU law.

Among the draft documents are also demands for European delicacies like Parmesan cheese and Champagne to be given a protected status in British law after Brexit, according to the FT.

Intellectual property rights must not be "undermined by the withdrawal of the UK from the EU", the papers state.

To make safeguards for geographic food and drink specialities that have protections, such as parma ham, enforceable "specific domestic legislation" may be needed.

Mr Barnier is expected to be quizzed about the contents of the documents at a press conference in Brussels this afternoon.

According to BBC reports, the EU papers insist that nothing in Britain's withdrawal deal should affect Ireland's place in the single market and customs union.

The documents propose allowing people to continue to cross the Irish border to work, study and receive medical treatment, it was reported.

And they are understood to float the idea of specific commitments to be written into the departure deal to protect cross-border co-operation in areas like health, education, transport and fishing.

Meanwhile, Antonio Tajani, the President of the European Parliament, has said he will ask the European Council to postpone its assessment of whether "sufficient progress" has been made to move on to trade talks from October to December.

Mr Tajani's comments came as former European Council president Herman van Rompuy warned that chances of sufficient progress being made by October were "in the neighbourhood of zero".

But First Secretary of State Damian Green told BBC Radio 4's Today programme: "That's too pessimistic.

"Clearly, these are complex negotiations but there are several rounds to go. We've said we want to increase the pace of them.

"There have been some significant agreements made already, so negotiations obviously will be tough but let's see what happens between now and October."

Mr Tajani said that agreement had to be reached on the UK's financial settlement, citizens' rights and the Irish border before moving on to the second phase of negotiations.

"Without an agreement on this, we cannot talk about the future," he told the Politico website on Wednesday.

"So far we have noted that no concrete proposals have arrived, only very foggy proposals.

"I will ask the Council tomorrow (to extend the deadline) but it's not our fault, but due to delays.

"And the Brits are the ones who will be mostly affected by it. It is not a tragedy, but we cannot postpone further than December.

Cecilia Malmstrom, the EU trade commissioner, stressed that Britain would not be able to negotiate new trade deals with third countries until after Brexit.

At that point, the UK would have to "renegotiate" agreements it currently enjoys due to its EU membership, such as the deal expected to come into force shortly with Japan, she said.

"The UK is a member of the European Union," Ms Malmstrom told a Brussels press conference. "It will remain a member until the day it leaves and during that membership the UK like anybody else has the advantages of all the international agreements we have done, including free trade agreements.

"The moment they leave, they also leave - for instance - the deal with Japan, if it has entered into force by that time. Then they will have to renegotiate and that will be business between Japan and the UK."

She added: "It is very clear as long as they are a member they cannot negotiate a trade agreement on their own."