The tune is by Flanders and Swann, it's The Hippopotamus, although the words are obviously a new version.Rolf Harris singing the Hippopotamus song - http://www.youtube.com/watch?v=AFUQasY3stA Abusive comment hidden. (Show it anyway.)
Rolf Harris singing the Hippopotamus song - http://www.youtube.com/watch?v=AFUQasY3stA