http://www.Kernowrat.co.uk For Berkefeld filters, good service, quick delivery, and the cheapest around that I could find. Their website isn't brilliant but they also have a fleabay shop which is better.
Surplus & Outdoors. A pretty decent site, I've bought a few things from them, small equipment and some clothing. Haven't had any problems whatsoever - for instance, I bought two army jumpers from them because I wasn't sure what size would fit me better and had no problems returning the one and getting a refund for it. Worth shopping with in my opinion.
I bought an NBC filter from them a year or so ago. Just about the ONLY place in the UK that you can buy a brand new, guaranteed, full NBC filter (fits NATO 40mm) for your gas mask. I had some questions and they responded quickly and helpfully. Recommended.
Medical Items, FAK's etc. - http://www.spservices.co.uk/ - great customer service - not affiliated to them but would highly recommend.
Used To Sell Woolrich Pants(Like 5.11's but a lot more comfier), Sell 5.11 gear etc - https://www.uktactical.com/ - Very Good Customer Service, Speedy delivery and well just recently.
Call me cheap but I have a load of stuff from the local pound shops. OK so you aint gonna get a Kukri or a Bergen but there is a load of stuff that is useful to have in your kit.
Purlon Cord like paracord.
Collapsable cups.
Mosquito Repellent
Emergency Shelter
Camera Cases (even in camo)
Poncho
Disposable Lighters
Survival blankets
Collapsable Water Carriers
and more chocolate than you can shake a stick at, yummy.