Dave, probably just coincidence that a No.36 and a Citron Foug share the initials PF.
Assuming they represent the maker's initials on the No.36, then there's a reasonable probability of it being The Park Foundry Co, Belper, Derbyshire. PF produced 100,000 No.36 between July and September 1940, but I wasn't aware until now that they were a WWI Mills manufacturer. However, they were a pre-WWI iron foundry, so perhaps not unreasonable that they should make Mills' bodies, if not all the other components.
Tom.