As I understood it, the callsign Swanwick Mil was to avoid confusion with London Mil who were only working the east side of the country. I think when the London FIR units are co-located again at Swanwick everyone will keep London Mil as a callsign. D&D will also stay as London Centre when they move. Do you know, I can't remember what LJAOs callsign used to be, I'm sure it wasn't London Mil, perhaps London Mil can remind us?
As far as nPC is concerned, aren't they changing the FIR/UIR boundary as well?