Perhaps it's in part because the acting is so fine - playing characters we like, yet in a very unsavory situation - this movie stays with me these 20 or so years since I saw it on television.
This is also one of the relatively few movies before the late 1950s that I can recall that really (purport to) go out into the British countryside: The Clouded Yellow is another example - and a similar style of movie to this (and also very good). Aside from these, I can think of only the Scottish scenes in The 39 Steps, I Know Where I'm Going, How Green Was My Valley, The Stars Look Down. (Suddenly in the late 1950s/1960s, British movies exploded out of London and went a-venturing - in such as This Sporting Life, Look Back in Anger, Tunes of Glory, A Kind of Loving, Room at the Top, Billy Liar, Whistle Down the Wind, The Loneliness of the Long Distance Runner, Becket, The Lion in Winter, Saturday Night and Sunday Morning, Tom Jones, Get Carter, Alfie).
Like The Clouded Yellow, this is the kind of movie patented by Hitchcock - filled with psychological suspense, fast moving plot, attractive actors, physical danger, significant looks, deception.
I've never seen a video or DVD available - but it's definitely worthwhile seeing it if you get the chance (perhaps on television).