David Cameron was pretending not to know what Magna Carta means when he was interviewed on US television, Boris Johnson has claimed.
The London mayor said the Prime Minister did know the answers to questions posed by TV host David Letterman but got them wrong so he would appear more down-to-earth.
Mr Cameron received some criticism for his appearance on The Late Show with David Letterman after he fluffed questions on what Magna Carta meant and who wrote Rule Britannia.
His fellow Old Etonian and Oxford University contemporary Mr Johnson claimed Mr Cameron really knew Magna Carta meant Great Charter.
Classics scholar Mr Johnson said: "I think he was only pretending. I think he knew full well what Magna Carta means.
"It was a brilliant move in order to show his demotic credentials and that he didn't have Latin bursting out of every orifice."
Mr Johnson made the comments during a radio interview where he himself failed to answer a question on British modern sporting history.
The politician did not know who scored a hat-trick for England in the 1966 World Cup final.
Mr Johnson claimed defender Bobby Moore netted three. In fact, Moore was the captain who held aloft the Jules Rimet trophy at Wembley.
Perhaps realising the revelation could damage his dreams of claiming the keys to No 10 Downing Street, the 48-year-old mayor protested: "I was only two."
In the same interview he also apologised to businesses that suffered during the Olympic Games, but denied claims the capital became a "ghost town".
Mr Johnson said: "I'm not going to pretend it was a bonanza for everybody and for those that feel hard done by, I'm sorry for the losses or low takings they had.
"But the overall economic benefit to London of people around the world seeing a city that can deliver an amazing event like that so successfully was incredibly positive."