I've just seen this tail in my garden and it looks to me like it belongs to a fox. We certainly get foxes in the garden, but there is no evidence of the rest of it, or any other animal nearby. It's about 20cm long.
Is this perhaps a consequence of a fight between two foxes? Or is it from another animal entirely? I live in Brighton so I can't imagine there are a lot of other options! Would love to hear if anyone else has seen this before.