The whooper swan is mainly a winter visitor to the UK from Iceland. This is a lone individual I saw at Attenborough Nature Reserve in January last year.
Only once before have I seen whooper swans at ANR and that was this distant view of a small flock of six in March 2018. In the UK they are mainly confined to the Severn Estuary and East Anglia. The name arises from its noisy, whooping call.
This is an example of the similar Bewick’s swan. It was named in 1830 by naturalist & author William Yarrell after the engraver Thomas Bewick, who specialised in birds and animal illustrations. They are also winter visitors to the UK, migrating from eastern Russia. The Bewick’s swan is smaller than the whooper swan and has more black colouring on the bill. Image and information from Wikipedia.
The differences between the three species is most marked in the head shape and bill markings.