London Camera Exchange at Frankfort Gate sell Ilford B&W films, papers and chemistry, but is limited to FP4 Plus and HP5 Plus. They also sell Fuji colour films.
Spectrum are the local pro-lab, I think they do colour and C-41 B&W films, but not regular B&W. They also do E-6 colour reversal films.
As for photo-locations, look around the city centre along with Plymouth Hoe and Sutton Harbour etc.