Boris Johnson has urged European Commission president Jean-Claude Juncker to visit Britain to see how it has been "damaged" by the EU.
Mr Johnson said it would be "wonderful" if Mr Juncker came to meet families and businesses in the UK that have been hurt by EU membership to give him a "better understanding" of the impact of EU membership.
The former London mayor's comparare the EU's efforts to unify Europe to earlier attempts by Napoleon and Hitler.
Juncker said: "I'm reading in (the) papers that Boris Johnson spent part of his life in Brussels. 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.''
Mr Johnson wrote to the EU "You very imaginatively suggested today that I might like to visit Brussels, so that I could better inform myself of your work and your plans for the future development of the EU".
"I would like to take you up on your suggestion". "As you may know, I believe that the time has come for a real and thoroughgoing reform of Britain's relations with the European Union and that the only way we in this country can take back control of our democracy is to vote leave on June 23".
"I believe that we should develop a more harmonious and practical relationship between Britain and other European countries, and that this should be done on the basis of free trade and intensive intergovernmental cooperation".
"I would much welcome the chance to explain how this would be of benefit both to this country and the rest of the EU".
"I would also like to extend an invitation to you. Many parts of Britain - many families and small businesses - have been damaged by our EU membership".
"It would be wonderful if you could visit some of these places and meet some of those people with me. I have no doubt it will help inform the debate and give you a better understanding as you attempt to reform the machinery of the EU".
"As you mentioned, I have happy memories of the beautiful city of Brussels and I look forward to seeing you in the near future", said Mr Johnson.
President Juncker's head of cabinet, Martin Selmayr, wrote on Twitter: "#G7 2017 with Trump, Le Pen, Boris Johnson, Beppe Grillo? A horror scenario that shows well why it is worth fighting populism. #withJuncker."