My Collegue MWJB told me about this post and as he rightly thought this is a Segestria florentina.The Tube Web Spider. I think that the thing that is a little odd about this photograph is that the body looks perhaps a little small for the leg size. I think that this is probably a female that has recently undergone her final moult. therefore the slightly small abdomen. In the background around the spider you can see the 'tripwires' that radiate out from atound its tube web lair that it uses to detect its prey.
Although my heart lies with Salticidae the Jumping Spiders I have to say that this is certainly one of our most exciting spiders and definitely when fully grown one of the heaviest UK spiders. I recently recorded one with a body length of 32mm!