Withams sell stuff like this and I asked. Basically they can't be sold for use in the uk as they are made for 'third world spec' - they don't have the kitemarks and safety certificates for use in Europe. The cost to get them approved would be unrealistic as each component will have to be changed for a stamped one ( no doubt it's actually the same part, stamped or not).
Usually these situations crop up as some foreign country or business outside the ue has ordered a load ( say China or somewhere) and then the order is cancelled. The cars can't enter the man stream as they don't have uk type approval (or something) and it can't be gained retrospectively, as a result they can't be road registered. Hence the sale outside of the uk.
Withams had an Aston Martin in the same situation a few months ago, it sold for about. £100k less than normal and was only delivery miles. They reguy have jags and other stuff like that for the same reason.