Like the DVLA site. Fed in reg GH 8803 and came up with Rolls Royce first registered in 1930, which fits the description of the 101 Sqn Merlin car. The photo looks right (still can't work out how to put it on pprune and cant find the website I got it off anymore!) Just suprised that there isn't more about this great looking car on the web.
Might try a call to Top Gear or summit like that.