Can anyone remember a sketch where a British soldier is unaware that WW2 has ended and carries on his campaign which involves creeping up on Japanese tourists and shouting "jaaapaaaaneeeeeese" followed by a raspberry.

I have been searching for the clip for years. I think it may have been The Two Ronnies or Spike Milligan.

Sounds quite Spike to me, but I'm afraid I've no idea what programme or series it may be from.

I do believe that you are referring to Rutland Weekend Television, which can be found on YouTube.