I always thought that the fire bottle in the pt side of the galley was there for the Hyd, Aileron and Elevator bays and not the bomb bay, hence the three positions the hose can locate into marked 'H', 'A' and 'E'.
Cant remember one marked 'BB', had a look today, no.
TD in answer to your question to my knowldge there are no fire bottles fitted to a Nimrod in the bomb bay.