Nigel Farage has warned Jean-Claude Juncker his “bloody rude” behaviour and attempt to “bully the Brits” could force Britain to walk away from Brexit talks within months.
The former Ukip leader said the EU needs to make “grown-up, reasonable” demands or face the prospect of the UK withdrawing from the negotiations by the end of the year.
MEP Mr Farage also claimed the Eurovision Song Contest made Mr Juncker look “a bit silly” for mocking the English language, given that 90% of the songs were performed in English.
His attack came after European Commission president Mr Juncker said the Brexit process shows how “united and prepared” the EU will be.
European Council president Donald Tusk also insisted the conduct of the talks must “show the European Union at its best”, adding this involves “unity, political solidarity and fairness towards the United Kingdom”.
The remarks emerged as the European Parliament met to discuss last month’s Special European Council in which leaders of the EU 27 formally endorsed the bloc’s negotiating strategy for Brexit talks, set to commence after the UK General Election.
Relations between Brussels and London have been strained further by leaks about a difficult dinner in Downing Street attended by Mr Juncker, which reportedly ended with him saying he was “10 times more sceptical” of the likelihood of a successful Brexit.
Mr Juncker also used a conference speech to joke that “English is losing importance in Europe” as he opted to speak in French instead.
The UK is expected to be required to settle liabilities on withdrawal, with reports suggesting the “divorce bill” could be as much as 100 billion euro (£85 billion).
Speaking in the European Parliament, Mr Farage asked his fellow MEPs to imagine they were hosting a dinner party in which a “very important guest” had told others that you were “deluded” and “living in a different galaxy” within hours of it ending.
He described a situation in which the details of confidential conversations were “blabbed to an opposition newspaper”, adding: “And then a few days later, in a display of extreme petulance, you even deride the national language of the host – which, by the way, is looking a bit silly because last Saturday’s extravaganza knowns as the Eurovision Song Contest saw 90% of the songs sung in English.
“If you were the host and you’d been treated like that by somebody you thought was important and somebody you thought you could trust, I’d think you’d be asking yourself, were you dealing with a reasonable person.
“I don’t know, Mr Juncker, whether this is how you carry on in Luxembourg. I doubt it, because in any part of the civilised world, frankly, that behaviour would be considered to be bloody rude and the act of a bully.
“Well, I’ll tell you something, your attempt to bully the Brits through this negotiation is not working – 68% now of the British people want Brexit to happen.
“All of that on top of a ludicrous ransom that (EU chief negotiator) Monsieur (Michel) Barnier wants, that I’m told has now doubled to 100 billion euro.
“Either we get some grown-up, reasonable demands from the European Union or the United Kingdom will be forced to walk away before the end of this year.”