The car isn't the prototype, it's the first off production line and the girl in the car is Ann Hedges, the daughter of Len Hedges of Panelcraft, later to become Mrs Hulme.
I must admit that knowing it was a Nash-Healey, made finding the answer to this puzzle quite easy, I do use the Internet, but not the image search, I'm new on this forum and hope I haven't done anything wrong.