One such pack on the U.S. market, and probably available in the U.K. too, is the SpeeDemon from Ultimate Direction ($120, about 80 pounds Sterling). It's designed specifically for trail running, so has a low-profile design that stays close to your back for good balance and minimal bounce. Plus, it has a big hydration bladder built in. Side pockets and bungee straps give you lots of places to stash small things quickly. Another pack that's designed for similar activities is the Gregory Advent Pro ($129), a little larger than the SpeeDemon but designed with trail running and adventure racing in mind. It'll even hold two big hydration reservoirs and has a vented backpad so you won't get too overheated.
In terms of a "regular" pack that would work, I like Marmot's Talus ($120). It's a tough, compact pack, with 2,200 cubic inches of capacity and two water bottle pockets. And of course, you could always stick a hydration bladder into it.
Study hard, help little old ladies across the street, be polite to your parents. Do all that, and perhaps you too can be a Gear Guy!
SpeeDemon available from REI here.
Filed To: Trail Running