A KEY ally to Angela Merkel has hammered Jean-Claude Juncker over his decision to reveal details of a private Brexit dinner discussion with Theresa May.Stephan Mayer, the Christian Democrat Union’s home affairs spokesman, insisted both the European Union and United Kingdom should be conducting the negotiations “confidentially and not in public”. Mr Juncker, president of the European Commission, declared he is “10 times more sceptical” after joining the Prime Minister for dinner at Downing Street on Wednesday, it was reported. A detailed account of the meeting was published in German newspaper Frankfurter Allgemeine, where it claimed Mr Juncker accused Mrs May of “megaphone diplomacy” and a complacent approach to the negotiations. He also reportedly is said to have contacted Ms Merkel, telling the German Chancellor he believes “Theresa May is living in another galaxy”.Speaking on BBC Radio 4’s Today programme, Mr Mayer said: “Certainly it is not good when such details become public. “I think, in regards to the complexity of the upcoming negotiations, both partners and both sides should be interested leading negotiations quite confidentially and not in public. “They are complicated enough, and I think it worse when the negotiations are held in public.” Ms Merkel, in the wake of Mr Juncker’s meeting in Britain, claimed British people have “illusions” over whether the UK’s EU divorce could be agreed at the same time as its future relationship with the bloc.She told German MPs it would be a “waste of time” to maintain illusions that the two sets of negotiations could be held simultaneously.Ms Merkel said: “A third country – which is what the UK will be – cannot and will not have the same rights as an EU member state. “All 27 EU countries and the EU institutions agree about that. “We can only do an agreement on the future relationship with Britain when all questions about its exit have been cleared up satisfactorily. “The sooner the UK Government is ready for constructive solutions, the sooner we can meet its wish to talk about the future relationship. But first, we need to know how the UK Government envisages that relationship. It can only be done in that sequence.” Mr Mayer backed Ms Merkel to push for hard EU negotiations, not allowing Britain to leave the European project without consequence. “You leave with all the consequences,” he added. “I am also convinced that this Brexit isn’t in the interest of the European Union and Germany. “The consequences will be worse for the UK. If someone in Great Britain thinks it will be the winner or takes advantage of this Brexit, I am convinced this would be an illusion.” Mr Mayer, however, stressed the importance of Britain’s relationship with Germany, as one of the nation’s key trading partners.