Possibly Clubionidae but can't find any illustations that resemble this one. Length 12mm
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To be honest Coelotes was my first thought but when I look more closely at the markings an Amaurobius makes more sense (e.g chevrons towards the tail)
Thanks Matt. That looks much more likely based on appearance, habitat, size etc. It was lurking at the bottom of a plant pot with a cribellate web (had to look up what that meant)
..and if you put the lady in a small glass tube and look at her spinner area with a x10 you should be able to see the split cribellum.
(note that coelotes lurks in a silken cell during the day - but its not the ultrafine cribellate silk of a lace weaver)
Lat/Lng: 51.4737, -2.5858
OS grid ref: ST594751