A publicity shot taken during filming of the original title sequence in 1977.
As Martin said, working on the show was "continual, constant frustration." This shot is probably one taken while filming 'The Purging of CI5'. 
Be on guard at all times – even a seemingly peaceful, harmless Surrey golf course can be crawling with international hitmen. A rather silly publicity shoot for 'Blood Sports'. 
It is well known that Martin and Lewis performed their own stunts on the show. Occasionally things did go wrong – in this case, Lew and Gordon's hair having caught fire. A shot from the set of 'The Purging of CI5'.
Publicity shot during filming of 'Not a Very Civil Civil Servant'.
Publicity shot from 'A Hiding to Nothing'