Yeah, it was from a Christmas special of their radio show From Us To You... I think. The host was indeed Rolf Harris, an Australian comedian/singer/artist who was very big in England (and still is!). Tie Me Kangaroo Down Sport was one of Rolf's hits and on the show, the Beatles joined him in a comedy version of the song, which was broadcast complete with the hilarious mistakes. John's comments at the end always crack me up, he says in a very fake childrens-presenter voice "and you forgot the ending, didn't you Rolf"!