UK's only resident swan is the Mute Swan. Bewick's Swans and Whooper Swans over-winter in the UK. Bewick's tend to favour the southern half of the country, and Whoopers the northern half. Both Whoopers and Bewick's can be distinguished from the more common Mute Swans by having bright yellow patches on their bills. Bewick's yellow patches tend to be much smaller than those on the Whooper Swan. I saw these two (six in total) flying over the causeway, it was a dull day, and they were flying the wrong way, so not the best of views, but their gentle trumpeting is always a good way of identifying them.