Many of the other reviews refer to the thin and unbelievable plot and casting. I beg to differ. 90% of modern films are pure unbelievable west coast Amertican dross, just think of the fare from Will Ferrell, Adam Sandler, Cameron Diaz, Ben Stiller, Owen Wilson, and all the high school, college, so called coming of age movies awash with those stupid Californian accents, etc, etc, etc.
This is a British B/W film of the early 50s and has the benefit of Margaret Lockwood playing against type in a plot line which holds up well, it is a movie after all, escapism, and perfectly encapsulates the early post war, cold war fears and demons of the time, played in a gentle tongue in cheek way by the cast and director.
I enjoyed it immensely, and so will you. Give it a go, far superior to most modern movies.