Former London Mayor Boris Johnson told The Telegraph on Sunday that the Europeans' goals to unite the continent are not unlike Adolf Hitler's.
"Napoleon, Hitler, various people tried this out, and it ends tragically," he said. "The EU is an attempt to do this by different methods."
Johnson vocalized his opposition to Britain's involvement in the European Union in February, while he was still mayor, notably going against Prime Minister David Cameron. On June 23, British voters will weigh in as to whether the nation should leave the EU.