From time to time we get enquiries on here asking about British gunmakers/ cartridge makers.
One of the best reference sources are old telephone books. The central telephone book archive is in London at the BT (British Telecom) archive in London. They have virtually all the old telephone books back to 1880s but you can only access them in person. There are now however sources for telephone directories on line although many require a subscription. There is an archive of trade directories as well which is free. Generally speaking they are hard work but they do contain the information. The various names are not indexed so you have to call up the directory and go through it page by page.
I have an article in front of me on directory sources in a Geneology Magazine but its too long to reproduce here. if anybody would like a copy I will photocopy the artice and mail it.
Contact me by PM and I will happily send it. It would be useful for other non cartridge related research as well. Geneology for example. I know a lot of you are interested in that as well .