Solved - much bigger than an NB Magnette, it's a 1937 MG SA Tourer Charlesworth, chassis SA1407, "
.. first registered in England and by 1943, it had joined the Pacific Auto Rentals collection in California who rented unusual automobiles to Hollywood studios. It remained in the collection for 4 decades and was used in many feature films including Alfred Hitchcock's Rebecca starring Lawrence Olivier and Joan Fontaine, The Invisible Man with John Carradine, Cluny Brown with Charles Boyer and Peter Lawford, Love Letters with Joseph Cotton and Woman in Green with British Sherlock Holmes duo Basil Rathbone and Nigel Bruce."
Our collection of sightings.