The following are educated guesses -
SEIL - Selmore (Engineering) Industries Ltd., 23 & 43 Hollybush Gardens, Bethnal Green Road, London, E2. This company supplied the Admiralty, but what, I've no idea. I've made a few enquiries, but as of to date have been unable to find out anything of this company.
ERMAL – ERM is Enfield Rolling Mills, Al – is Alumininium. Thus it might be Enfield Rolling Mills (Aluminium) Ltd. The company did exist, whether they made cartridge cases or not, I don’t know.
CFP - No idea.
SQ - Horst, what is your source for this being Sanquhar?
CFP – I’ve no idea.
TimG