Snow Goose Anser caerulescens (or Chen caerulescens)
Snow Geese are popular in captivity and escapes occur frequently. However genuinely wild birds do occur occasionally and in Norfolk these are most likely to be found among the wintering Pink-footed Goose flocks (though one accompanied Whooper Swans a few years ago). They are rare though, and the earliest of the Norfolk birds shown below followed a gap of several years.
The majority of Snow Geese occurring in the UK are thought to be Greater Snow Geese A. c. atlantica but smaller individuals are occasionally attributed to the more westerly originating nominate form, Lesser Snow Goose A. c. caerulescens. The first bird shown below is small and is believed to be a Lesser Snow Goose, though both forms vary in size and I'm not sure how possible it is to be sure.
Blue (and/or intermediate) morph Snow Geese are particularly rare here and the individual shown here was possibly the first such wild bird to be seen in the county, apart from a bird of unknown origin with Taiga Bean Geese in the winter of 1973/74. Most blue morph Snow Geese are Lesser Snow Geese and the small size of this individual supports that identification.
Here's one from its native range in North America:
first-summer Snow Goose, Roberts Lake, Seaside (California, USA), 1st May 2005
The following are captive birds - having not previously noticed how orange the base of a Snow Goose's bill can look I considered whether these could be hybrids, but quickly discounted that as they showed no other sign of impurity. Further investigation revealed that it's not so unusual for a pure Snow Goose to show orangey tones at the base of the bill.