Since the camera doesn't use the "modern" shutter speeds, use sunny f16 (or whatever is appropriate for the north of England for this time of year and err on the side of more exposure rather than less. So if proper exposure on a modern camera might be 1/125 at f8, make it 1/100 at f8. With negative film, always err on the side of overexposure -- it actually does better that way. So maybe just rate the film at 100 speed and go from there.