So far I think we have the following UK made gear: -
PHD - down stuff
Aiguille Alpine - Sacks, bags, pouches, throwbags/lines, canoeing gear, etc.
Alpkit - socks only
Furtech - Paramo style of clothing
Cioch, slioch - niche clothing manufacturers (made to measure and ventile,
Mountain King - trekking poles made up in the NE England.
Howies (not sure onthis but it is a brand based in N Wales) - Clothing (ethical origins).
Bison Bushcraft - knives and other things
Hilltrek - clothing
Snowsled - clothing
Extreme Outdoor Clothing - clothing they do Karisma type of fleece tops and trews
Altberg - boots
Terra Nova - someof their tent range is made here but only the high end stuff I believe.
POD - sacks although not sure they are still made here. Part of the same group (Equip) as Rab is now.
Mardale - pertex/pile stuff like buffalo stuff.
Buffalo Systems - Arguably THE brand for pertex/pile stuff
Robert Saunders - Tents, but not sure if these are UK made these days
Draw Ltd - Rucksacks (see post 44).
Is that it? Seventeen British outdoor gear manufacturers.
Nearly forgot, I heard of a Cumbrian based manufacturer of kelly type of kettles but its a cottage industry sort of company.
Then you could always add the loads of British makers on this site, but they are probably not companies but people making and selling on for the love of the craft.