DaveG28 buying stuff through Royal mail at Tallent house is expensive I imagine. but if you want used stamps, try Dewaulders of Salisbury, or Robert Murray of Edinburgh. I'm sure there are others but I can say from experience that these two are OK and they have Websites.
Today I received the catalogue for Yorkshire Coast Stamps on 10th july, it has over 300 GB lots this time. If you are just starting collecting GB some of the Collections and accumulations would make a really good foundations. They don't have a website but the email is email@example.com
. If you haven't already got one you need a Stanley Gibbons GB concise catalogue. Don't be fooled by the Concise the specialized catalogues should come with Ice packs and Acetominophen.
Universal Postal Auctions have also released their next auction catalog today. It is downloadable from the net.