I finally decided that this is probably a juvenile Mandarin rather than an adult male in eclipse plumage. I took the shot on the banks of the Gloucester/Sharpness Canal about a mile or so from Slimbridge WWT. This exquisitely marked little duck was playing the usual “can I be your friend if I tag-along” with a group of Mallard….It’s funny how they do that, but given a total lack of their own species for company, I suppose it’s better than being lonely and more vulnerable.