Gwen Watford (Dolly Bantry) appears in this, "The Body in the Library" -- the first Miss Marple episode of this classic series -- and in "The Mirror Crack'd From Side to Side"-- the LAST episode.
Miss Marple's phone number changes over the course of the movies. In 'The Body in The Library' her number is St Mary Mead 35. In Season 3 (The 4:50 From Paddington) her number is St Mary Mead 236.
According to the Bournemouth Echo article , 12/06/2007, 'Location! Location! Location!' "The classic Body in the Library was filmed around the former Branksome council buildings in Shillito Road as well as the Royal Bath and Highcliffe Hotels in Bournemouth."
Andrew Cruickshank had a previous encounter with Miss Marple; in film Murder Most Foul with Margaret Rutherford he had a cameo role of a judge.
John Moffatt is no stranger to the works of Agatha Christie. He had a minor role in Murder on the Orient Express (1974). He also played Poirot on Radio 4.