I got Stu to write a little explanation of his process:
It's 100% 3D, but I render out all the elements seperately, so shadows, highlights, reflections, depth and fog are seperate images, then I compile them back up in Photoshop, so I can manipulate each element, applying filters, altering brightness, contrast, adding colour, that sort of thing, then it all gets flattened, then a few more filters are added.
He then added:
I'm still playing around, trying to find the right look...
Although... personally I think he has nailed it already!