Thanks to reader Tupperware Harry over at the Sweeney Forum.
In less then twenty four hours the Sweeney have turned up trumps and nabbed the villain they were after. They may now retire victorious to the pub for a rather grim pint of lager, endless fags and a sing song. As it turns out the picture I was looking for was never in an episode, but was a publicity shot taken from the first Sweeney! film during the "Fulham Blag".
Not the best picture in the world, but perfect for my purposes.
I shall fire this off to Matt at Elheim directly. Good night all.