Boris Johnson, a leading campaigner for Britain to leave the European Union at a June 23 referendum, said in an interview that the EU was following the path of Adolf Hitler and Napoleon by trying to create a European superstate.
The former London mayor, a member of Prime Minister David Cameron's Conservatives, told The Sunday Telegraph newspaper that the EU lacked democracy and a unifying authority and was doomed to fail.
"Napoleon, Hitler, various people tried this out, and it ends tragically," Johnson was quoted as saying in an interview.
"The EU is an attempt to do this by different methods. 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."
While fellow pro-Brexit Conservative colleagues supported Johnson's comments, he drew criticism from the "In" camp.
Hilary Benn, foreign affairs spokesman for the opposition Labour Party, said Johnson had lost his moral compass.
"After the horror of the Second World War, the EU helped to bring an end to centuries of conflict in Europe and for Boris Johnson to make this comparison is both offensive and desperate," Benn said in a statement.