On the Fiddle (1965)

Tricked into ing the RAF by a wily judge, wide boy Horace Pope sets his sights on the main chance, teams with slow-witted, good-hearted gypsy Pedlar Pascoe, and works up a lucrative racket in conning both his colleagues and the RAF. By means of various devious schemes Pope and Pascoe manage to avoid the front lines until they are sent to - where they find themselves making unexpected and uncomfortably close with the enemy.