Common Sun-jumper Heliophanus flavipes
I thought this looked distinctive enough that I might have a chance of identifying it from a photo, but it seems that I needed to retain the specimen and check it microscopically to be completely sure it wasn't one of the other members of the genus. That I didn't do, so unless someone more experienced advises me otherwise it won't go down as a record. Nevertheless, based on range and external appearance I think it is extremely likely to be flavipes.
presumed Common Sun-jumper Heliophanus flavipes (not confirmed), Foulden Common (Norfolk, UK), 27th May 2023