 By the mid-1940s, Sim was being cast in starring roles in films.His earliest successes as a leading man included the police detective in the thriller "Green for Danger" (1946); the headmaster of Nutbourne College, co-starring with Margaret Rutherford, in the farcical comedy "The Happiest Days of Your Life" (1950); and a writer of lurid crime fiction in the comedy "Laughter in Paradise" (1951).His other films included "Waterloo Road" (1944), "London Belongs to Me" (1948), Alfred Hitchcock's "Stage Fright" (1950), "Scrooge (A Christmas Carol)" (1951), "Folly to Be Wise" (1953) and "An Inspector Calls" (1954).