Clooney became embroiled in the long-running dispute over the Greek artefacts, which were removed from Athens in the early 1800s and are now housed at a museum in London, while promoting his new movie The Monuments Men.
In the film, the actor plays an art expert tracking down treasures stolen by the Nazis in World War Ii, and he called on British leaders to end a centuries-old row with Greece by handing the sculptures back.
His comments drew the wrath of Johnson, who said of Clooney, "Someone urgently needs to restore George Clooney's marbles. Here he is plugging a film about looted Nazi art without realising that Goring (Nazi politician Hermann Goring) himself had plans to plunder the British Museum. And where were the Nazis going to send the Elgin marbles? To Athens!... This Clooney is advocating nothing less than the Hitlerian agenda for London's cultural treasures. He should stuff the Hollywood script and stick to history."
The Oscar winner has now attacked Johnson in a scathing dismissal, saying, "I'm a great fan of the mayor, and I'm sure my right honourable friend had no real intention of comparing me to Hitler. I'd chalk it up to a little too much hyperbole washed down with a few whiskies... There are many pieces in nearly every country that this conversation should take place (in). The best place to start would be at the most obvious object. When polled the British people are overwhelmingly in favour of their return. The rest of the world follows suit. If you want to deal in facts. Those are the facts. But maybe it's just easier to compare me to Hitler."