Not Exactly Ruling Britannia: David Cameron Fails British History Test on David Letterman's Show One David tried his best to outsmart the other one. It's probably for the best that David Cameron didn't have to take a citizenship test in order to become Prime Minister of the United Kingdom. Because Cameron's knowledge of his homeland isn't exactly perfect. Or perhaps it was just a case of nerves Wednesday night as he became the first ever serving British PM to go on The Late Show with David Letterman. Cameron has been in New York to take part in the U.N. General Assembly but decided to embark on a diplomatic mission of another sort. He appeared on Letterman's show to "bang the drum" for British business and encourage Americans to visit his country, which is still reveling in its success after the recent Olympics and Paralympics games. If we were to guess, we'd imagine that Cameron's advisers had prepped their boss to expect the standard range of political queries from the late-night host - including, perhaps, the Andrew Mitchell controversy dominating many a news broadcast back in Britain (Mitchell has been accused of speaking out of turn to the police at Downing Street), his ever growing rivalry with Mayor of London, Boris Johnson (who himself went on Letterman recently) or the state of the coalition with the Conservatives" Liberal Democrat partners. But Letterman is notorious for his curveball questions. And instead, the host decided to pepper the PM with a history exam of sorts. To wit: After "Rule Britannia" was played by the band to welcome Cameron on stage, Letterman asked if he knew who composed the legendary piece of music. Cameron incorrectly guessed Edward Elgar as Letterman informed him it was indeed Thomas Arne, with lyrics written by James Thomson. And the wrong answers kept coming. Cameron couldn't give a translation for Magna Carta ("great charter") though he did know, as every Brit is taught in school, that it was drawn up in 1215, signed in Runnymede and was of utmost significance in the early pages of British democracy. "Boy, it would be good if you knew this!" said Letterman in reference to the translation - and Cameron, perhaps turning on a quintessentially British apologetic spirit, didn't have the audacity to disagree. Letterman proceeded to throw some softballs, gently ribbing his guest about whether Ireland is in England. "Don't make that mistake!" retorted Cameron, who seemed instead more keen to discuss his nation's historic, long-standing relations with the United States. LIST: Top 10 Moments from the U.K. General Election As for Cameron's views on the special relationship - which he spoke about on camera to TIME after becoming PM - he even managed to elicit a laugh from the audience with his assessment: "There were some good bits and some less than good bits, and obviously we had a bit of a falling out. I like to think we've got over that now. He'll be hoping his electorate is equally forgiving after fluffing some of his lines. Hopefully Customs agents won't give him too much hassle when he returns next week. MORE: Obama on Letterman: Top 10 Things You Missed If You Didn't Watch