I know for a fact my 335d came into Immingham about 3yrs ago as it had it on a sticker in the window prior to the dealer touching it. At that time I thought it strange as the word was Soton was the UK dock for BMW imports.
So who knows, but I still think logically, you either have a prep center or you don't... that place would have cost millions and millions, not to mention all the staff... so if you don't need it for southern cars, why do you need it for northern ones.
F10 M5 Competition White / Sakhir Orange
Loaded, Akra carbon titanium exhaust, Carbon trim, Carbon spoiler, RKP carbon front lip + diffusor.
F31 330d M Sport (Alpine White / Red)
Loaded, 405M 20", M perf: skirts, brakes red.