Don't you just love those off camera "mike still switched on" gaffs 
Wearing a microphone but not on camera, he was thought to be rehearsing an answer to a question on devolution.
Ahead of a speech in Leeds, he said: "We just thought people in Yorkshire hated everyone else, we didn't realise they hated each other so much."
It is not known whether Mr Cameron was making a joke and Downing Street has refused to comment.
As expected, Twitter has come alive and hasn't failed to disappoint
But my favourite so far...
