This is a mid-1970s Vauxhall prototype, designed to be a Viscount-replacing range-topper, about the Victor/Ventora/VX models.
Bizarrely I saw this actual car parked in Edware Road, London, in the mid-1980s, but sadly didn't take a photo of it. I forget the exact name, but it was VX something, and featured in Motor magazine as well.