The London Mayor, Boris Johnson, elicited groans from an American audience after he told them America was London's greatest creation.

Johnson, who was on the Late Show promoting upcoming events in London, said "I regard America as the proudest creation of London. It was the ideals of liberty and democracy and habeas corpus and freedom of speech from 18th century London that were transmitted, would you not say?"

But veteran talk-show host David Letterman got his revenge when he raised the biggest laugh of the night by asking Johnson how long he had been cutting his own hair.

"I think that was a low blow," Johnson replied, before continuing, "I was beginning to think I'd got through this more or less unscathed."

Johnson also said that he regretted having said he would only be mayor for two terms when asked if he'd run again.