The European Union (EU) is reportedly engulfed by infighting as it emerged Mr Barnier “despises” Mr Juncker’s chief of staff Martin Selmayr.
The German bureaucrat – who is believed to be behind the leak about Theresa May’s and Jean-r Juncker’s dinner – is said to be intent on punishing Britain for voting Leave.
And he is said to be undermining rival Mr Barnier as he architects an EU punishment strategy to ensure Britain stumps up an eye-watering divorce settlement.
One Brexit official told Politico: “Selmayr is interfering in everything.”
And writing for the Daily Telegraph, Mrs May’s former chief of staff, Nick Timothy, said: “The displeasure directed at Selmayr has not only come from member states: Michel Barnier, responsible for negotiating on behalf of the Commission, despises him and believes he is trying to wreck the chances of Britain and the EU reaching a sensible agreement.”
Reports suggest that Mr Barnier’s and Mr Selmayr’s relationship soured after the German led Mr Juncker’s 2014 campaign to become EU Commission President, defeating the EU’s chief Brexit negotiator in the process.
Meanwhile, Mr Selmayr is suspected of attempts to remove any references to Mr Barnier from the EU Council conclusions on Brexit.
He is also accused of scuppering verbal agreements between Mrs May’s chief Olly Robbins and Mr Barnier’s deputy Sabine Weyand – his close ally – according to Politico.
Mr Juncker’s right-hand man has strongly denied reports that he or the “EU side” leaked damning details of a second dinner between his boss and Mrs May to “undermine” the Brexit talks.
Mr Selmayr, who is known as a ruthless operator, was widely blamed for leaking details of the pair’s first dinner at Downing Street to the same German newspaper and journalist back in May.
He wrote on Twitter: “This is false. I know it does’t fit your cliché, @NickJTimothy. But @JunckerEU & I have no interest in weakening PM.
“But it seems some have interest in undermining constructive relations @JunckerEU & PM May. Who? is the real question.
“I deny that 1/ we leaked this; 2/ Juncker ever said this; 3/ we are punitive on Brexit. It’s an attempt 2 frame EU side & 2 undermine talks.”
EU officials have attempted to quash rumours Mr Barnier and Mr Selmayr’s relationship is in tatters.
Commission spokeswoman Mina Andreeva added: “This is wishful thinking by those who don’t want the negotiations to succeed. Martin Selmayr and Michel Barnier are an excellent team.”