Theresa May has been accused of being "incompetent and unprepared", after claims her Brexit dinner with EU chief Jean-Claude Juncker was a disaster.
The Prime Minister has come under fire for failing to understand the way the EU works and for being on a "different galaxy" to other EU member states after details of her discussions with Mr Juncker were leaked at the weekend.
According to an article in a German newspaper, Mrs May used the meeting to push for an early deal on the rights of British citizens in the EU and claimed the UK did not have to pay "a penny" of the Brexit bill.
The report claimed that Mr Juncker thinks Brexit talks will collapse and that when he left the dinner he said that he was "10 times more sceptical than I was before."
Speaking to Sky News, Liberal Democrat Europe spokesman Nick Clegg accused Mrs May of being "incompetent and unprepared".
He said Number 10 appeared to be treating the rest of the EU in a "very high-handed way" and added: "You cannot treat the rest of the EU as if you were sort of ordering about Home Office officials, and that's the way that Number 10 seems to be operating.
"You cannot bark instructions at 27 other proud, independent governments and parliaments and expect them to do what you want."
According to the Frankfurter Allgemeine Sonntagszeitung newspaper, European Commission officials were astonished at Mrs May's ambition for the talks and were quoted as saying Mrs May was from a "different galaxy" to the rest of the EU.
They accused her of having "no plan" and said it was unrealistic to reach a rapid resolution on the status of expatriates, an exit strategy and a trade deal within two years.
The FAZ newspaper reported that Mrs May used the dinner to push for an early deal to secure the rights of British workers across the continent.
But Mr Juncker made clear that this could not be settled by June as suggested, given the complex negotiations on topics such as healthcare.
Mr Juncker and Mr Barnier, the chief EU negotiator, were described as astounded by the Prime Minister's assertion that the UK did not have to pay "a penny" of the Brexit divorce bill.
That claim was slapped down by Mr Juncker, who argued there would be no UK-EU trade deal without a deal on the money.
The FAZ report concluded that "Brexit cannot be a success".
Mrs May dismissed the reports as "gossip" and said: "Just look at what the European Commission themselves said immediately after the dinner took place, which was the talks had been constructive.
"But it also shows these negotiations are at times going to be tough. In order to get the best deal for Britain, we've got to make sure we've got that strong and stable leadership."
In a dig at Mrs May's "strong and stable" election slogan, the European Parliament's Brexit negotiator Guy Verhofstadt tweeted: "Any Brexit deal requires a strong and stable understanding of the complex issues involved. The clock is ticking - it's time to get real."
Labour's shadow Brexit secretary, Sir Keir Starmer, said: "Whatever the purpose of these leaks, 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.
"Theresa May talks about strengthening her hand, but in reality she has misjudged her hand at every turn, weakening Britain's position."
For the SNP, Scotland's minister for UK negotiations with the EU Michael Russell said: "This looming catastrophe shows precisely why Theresa May mustn't be allowed to block the decision of the Scottish Parliament to give people in Scotland a choice over their future when the terms of Brexit are clear.
"Leaving the EU with no deal - and no agreement on access to the single market - would be an unprecedented act of self-harm which would devastate the UK and Scottish economy.
"It is absolutely essential that we have a strong opposition at Westminster who can hold this kamikaze Tory leader to account and put the Brexit talks under real scrutiny."
In a speech on Tuesday, Mr Clegg warned that Brexit would hit living standards for millions and put a £59bn dent in public finances.
He quoted research from the Centre for Economics and Business Research, saying the typical household would be £500 worse of in 2017 than in 2016 because of Brexit.
He said he was surprised Mrs May went back on her work not to hold a general election before 2020.
He said: "This election shows the Conservatives reaching new heights of complacency: taking the support of voters for granted; assuming they have a right to govern without opposition; pulling the wool over the eyes of the people who will suffer most from a hard Brexit."