The Astonished Heart: A study in failure

While Noel Coward's two collaborations with David Lean, In Which We Serve and Brief Encounter, are rightly regarded as masterworks of British cinema, his third original screenplay, The Astonished Heart, is rarely discussed, and is generally regarded as something of an embarrassment, not least by Coward himself.
This is a little surprising, given the film's similarities with Brief Encounter - both feature Celia Johnson and Joyce Carey, and both are adapted from plays in the To-night at 8:30 sequence. This paper examines the reasons fro The Astonished Heart's failure, and what this can tell us about the earlier films, and Brief Encounter in particular - to put it at its most basic, what did that film do right that the Astonished Heart did so wrong?