Note the red bill and chestnut head, the birds underside is very dark with white underwings.
The Male Red-crested Pochard in Winter has a bright chestnut-red 'coiffed' head and a red bill. It's underside and breast is black and the flanks are white.
Adult Male Winter
General distribution: Usually considered a resident bird with only birds in the very North moving South. Escaped birds from collections have become established in several parts of Southern UK, particularly the South East. Genuine vagrants do occur, usually in the Autumn and Winter.
Habitat: Breeds in large reed fringed lakes and occasionally sheltered coastal bays. In the UK it is most often seen on freshwater but in Europe it frequently winters on the sea.
Notes: The Red-crested Pochard is a diving duck. It frequently cross breeds with other ducks especially within the Pochard Genus.