But I'll let my spider expert Ian continue the explanation. It's from the family Philodromidae, and more specifically one of the Philodromus aureolus group, which comprises at least four species in the UK: much the most frequent are P. aureolus and P. cespitum, while P. praedatus is reasonably common on oak, and P. longipalpis is rare on trees. Males are straightforward to identify but females like this one are the only fair-sized spiders which need dissecting to be absolutely certain of specific identification. This one probably isn't praedatus which never has such solidly dark bands down the sides of the carapace, and can reasonably discount longipalpis on range and habitat, so it will be either aureolus or cespitum. Both are very variable in colour and occur in a wide range of habitats on vegetation - field layer, shrubs and trees. As the name suggests these are amongst our fastest runners and can certainly move rapidly. They don't spin webs, using silk primarily as a safety line or to spin their eggsac.