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.
F31 330d M Sport (Alpine White / Red)
Packages - Parking, Security, Safety, Visibility, Pro Nav, M brakes, Adaptive S, Sport steering, Comfort Access, Sun glass, Mirrors, Heated seats, Surround-view, HUD, HK sound, Speed display. Mods - 405 wheels, M performance aerodynamics. M perf brakes red.
My toy - E92 M3 - (M.White + red)