This is verging on a trick question. How many people, who hadn't heard it before, would be thinking of an aquatic animal?
No one did in the game I took part in.
For a start, do seals eat on the islands? Surely they eat in the water.
According to Wikipedia, "the largest carnivores [of Great Britain] are the badger, red fox and the Scottish wildcat".
However, I did find several websites that name the grey seal as Britain's largest carnivore: for example BBC News, countryfile.com, Scottish Natural Heritage, and the Natural History Society of Northumbria.
© Macclesfield Quiz League 2017