Hey Maurice,
Long time no hear.
Well, while I do not know whether you can locate your car's 1stpoint of sale by your still current licence number (if so...)
I would rather go via the official dealership.
Please what does your datacard show? What are the numbers for the order code ("Auftragsnummer"). Then I would go to "Mercedes-Benz UK" and ask them to "decipher" to which dealership within the UK your car was shipped.
Good luck & keep us informed
Achim