Sorry I can't help with your query, steereomono (having searched in vain). The only sketch shows that come to mind are Spike Milligan's Q series, Rutland Weekend Television and End of Part One, with Denise Coffey and Sue Holderness. Could it be any of them?
The YouTube clip Kitty Whiskers posted was lost during the recent forum changes,
so I am reposting the video here, as this thread won't make any sense without it:
In case it disappears again, the video is titled 'Alan A'Dale'.
An impressive publicity picture of Joe Melia -
in colour - for his role as villain
Mo Liski in
The Mind of Mr. J.G. Reeder episode
The Green Mamba (1969):

Later that year, he was a guest in the
Public Eye episode
The Comedian's Graveyard.