Seeking Harry Worth scene

I remember a really funny scene from a Harry Worth episode - probably around the late 60s. He goes into a record shop to buy a record for 'Aunty', and hums the tune to the shopkeeper, as he can't remember the name. The shopkeeper says something like 'Hmmm ... I think I know the one - is it this?' He then puts on a disc, and the song is .... simply a voice humming that tune! Harry listens for a while and then says 'Err ... yes, I think it is that one!' Hilarious!! I would love to know the episode name so I can track down its DVD availability. Thanks to anyone who can help

Strange time for comedy, the early 70s. Monty Python and this.