This looks remarkably like Zoropsis spinimana, see Zoropsis spinimana established indoors in Britain, a spider well established in the London area and also in Sussex, but Bristol is a completely new part of the country for the spider! There are other southern European Zoropsis species, so really examination of an adult is necessary to be sure, especially since the pattern doesn't look quite typical for Z. spinimana.
Are you able to post me the spider for definite confirmation (if it is adult), to Peter Harvey, 32 Lodge Lane, Grays, Essex RM16 2YP ? Inside a plastic container with a couple of small air holes, inside a padded envelope would be fine.
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