should be a straightforward job then, as I say, chassis number on my s1 is on the front spring hanger so you may be able to see it and get the original number, I assume the little plate on the bulkhead - in front of the gear and 4wd knobs - with the chassis number on it isn't there?. if the dvla don't have it registered it might be more tortuous, letter from gaydon confirming its identity, or if the original reg is no longer available you should be able to get an age related one, wouldn't have thought you would have to have a q plate.