It is from the movie "Executioner", probably a b-movie from the 1970s, starring George Peppard and the unknown back then Joan Collins. ( http://www.imdb.com/title/tt0065711 ). The film is about a British intelligence agent who has to track down a fellow spy suspected of being a double agent. It also stars Gisela Dali, a well known greek soft porn actress, famous in the 70s.
Note in the youtube video provided how Corfu Town looked back in the 70s with traffic flowing through the now pedestrianised Liston.
Do you have any more infos and stories about that particular film? Any memories from the shootings?