However, since posting this puzzle I have found out that the picture may not be of a genuine car but a photo-shopped image of what it might have looked like..
I know it's an old thread, I just thought I'd clear this up for anyone who was interested. This is definitely a photoshopped image, created before the real images were discovered - originally intended to accompany an article that was three months in the making. Toward the end of this period, however, real photographs emerged.
How do I know this? I did the photoshop, collaborating with the article's author over detail and making some reference to the original drawings we could find. In important areas it was quite close, differing only in details such as front end treatment as suggested by the author of the piece it was to go with. Started off as a series III Morris Oxford.