Boris Johnson's grasp on EU reality questioned
The president of the European Commission Jean-Claude Juncker and his top official have made a strong personal attack on Boris Johnson.
Mr Juncker questioned whether the former London mayor's depiction of the EU is "in line with reality".
His chief of staff Martin Selmeyr said the idea of Mr Johnson becoming prime minister was a "horror scenario".
Mr Johnson said his pro-Leave views are in line with reality and that the EU is turning into a federal superstate.
"What the British people want to hear is slightly less from international observers and more about the arguments," he said.
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The war of words broke out during a press conference at the G7 summit in Japan when Mr Juncker was asked to comment on Mr Johnson's comparison of the EU's efforts to unify Europe with earlier attempts by Napoleon and Hitler.
The European Commission chief said he had read in the papers "that Boris Johnson spent part of his life in Brussels", adding: "It's time for him to come back to Brussels, in order to check in Brussels if everything he's telling British people is in line with reality.
"I don't think so, so he would be welcome in Brussels at any time."
The exchanges follow an interview Mr Johnson gave the Telegraph earlier this month, in which he said European history had seen repeated attempts to rediscover the "golden age of peace and prosperity under the Romans".
"Napoleon, Hitler, various people tried this out, and it ends tragically. The EU is an attempt to do this by different methods," he said.
"But fundamentally what is lacking is the eternal problem, which is that there is no underlying loyalty to the idea of Europe.
"There is no single authority that anybody respects or understands. That is causing this massive democratic void."
Mr Juncker was asked whether the European institutions would be able to work with Mr Johnson if he became prime minister, in light of his remarks. Mr Juncker said: "The atmosphere of our talks would be better if Britain is staying in the European Union."
In a later tweet, Mr Selmeyr wrote that the idea of Mr Johnson becoming British prime minister was a "horror scenario" - and compared him to the French Front National politician, Marine Le Pen.
Mr Johnson, who spent several years in Brussels as EU correspondent for the Daily Telegraph before his foray into politics, dismissed both EU figures as "unelected bureaucrats".
He said there was no question that Brussels wants to go ahead with plans for "a federal united states of Europe".
Arguing that the EU is "deeply anti-democratic", he urged politicians to "be straight with the public" that the 23 June referendum "is their last chance really to go for a different approach".