I've just been looking into other possibilities, since the front end looked like the Willment-Climax, and the rear end like a WRE-Maserati. In fact these cars are related, which I didn't know, and the story of these cars is recounted in brief on an AP puzzle for the WRE sports car.
The original WRE was bodied by Williams & Pritchard, but later cars were bodied in Italy by a small coachbuilder by the name of Gentelini e Allegretti, and apparently these were slightly different in appearance. They were RHD just like this mystery car. Not that any of this leads us to the answer, but it has got me thinking. (I can only find the puzzle photo on one site, and it does not actually confirm categorically that these are Scaglietti's workshops.)