One parent appears to be Pochard, but what's the other? Perhaps Tufted Duck? Either mummy or daddy was playing away - maybe both.
Similar size to the Tufted Ducks, perhaps a little smaller. Profile is very Pochard-like. Blaze is very Tufted-like. Body is Tufted, head is Pochard.
An instructive one, anyway. Don't take Scaup reports at face value on the Exe for a while, eh?
Thanks to James for mentioning the bird this morning...