Story highlights Anti-corruption summit begins Thursday in London

Nigeria spokesman: Cameron "must be looking at an old snapshot of Nigeria"

Nigeria, Afghanistan both ranked poorly by Transparency International

(CNN) Well, whoops. British Prime Minister David Cameron may have been a little too honest Tuesday in his comments about Nigeria and Afghanistan while speaking to Her Majesty Queen Elizabeth.

At a reception, a television crew picked up a conversation between the Prime Minister and the Queen.

"We had a very successful cabinet meeting this morning talking about the anti-corruption summit ...," Cameron told Her Majesty. Then, with a bit of a chortle, he said, "We have got the leaders of some fantastically corrupt countries coming to Britain ... Nigeria and Afghanistan, possibly the two most corrupt countries in the world."

The Queen's response to these comments is not clearly audible, though the Archbishop of Canterbury, who was also part of the conversation, can be heard saying that the current Nigerian President is not corrupt.

Asked whether the Prime Minister was aware his remarks were being recorded, a Downing Street spokesman said there were multiple cameras in the room.

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