Wikipedia claims that fencer and fight choreographer Bob Anderson played an Imperial Officer in Star Wars. This page movie-dude.co.uk shows a Rebel Officer claiming it's Bob Anderson but the quality is so low I can't say whether it's him or not.
So whom did he play, Imperial or Rebel?
As a bonus question, is there any conclusive proof of who was wearing the costume (Anderson or Prowse) in the original Star Wars movie in the iconic fight between Vader and Kenobi?