Help identifying these ducks please

Looks like one, doesn't? I'm limited in my ID skills though but you picture sparked my interest and only looked at my few ID books. One of them being Crossley guide for Britain and it shows an image not dissimilar, it also says they are rare visitors, so have you spotted something special I wonder. I hope someone is able to ID it for you.

Mystery bird looks to me to be a female Pochard but I'm not 100%
Sometime it helps to say where these odd birds have been seen as it can help narrow it down. Ferruginous duck has been reported on Norfolk but occasionally 'exotics' are found in water parks i.e. Regents Park and they might extend out.
Mallards, Porchards, Tufted duck will crossbreed to produce Hybrids just to challenge skills