Cackling Goose (Lesser Canada Goose, Small Canada Goose) Branta hutchinsii
The smaller forms of Canada Goose are now split from the larger forms ('Greater' Canada Goose Branta canadensis). There are many different subspecies of each and the identification, taxonomy and nomenclature of the complex is confusing and still in a state of flux.
Initially (at least in Britain) 'Lesser Canada Goose' seemed to gain favour for the species name for the smaller species but recently 'Cackling Goose' seems to be in vogue. Neither are ideal as both have previously been used for individual subspecies (Lesser Canada Goose for parvipes, which some authorities lump with the larger species, and Cackling Goose for minima). For this reason some have proposed the name Small Canada Goose, but although that meets my approval it doesn't seem to have taken on.
Small Canada Geese occur in the UK most winters but mostly in Scotland. Occasionally they are seen further south, including in Norfolk. Many of them are undoubtedly wild birds and these are often found with Barnacle Geese or Pink-footed Geese. Others may have escaped from captivity and certainly the very small dark geese of the form minima escape fairly often. When a form that is known to occur here naturally turns up on its own or with feral geese (as in the case of the birds shown below) it is much harder to know whether it's a wild bird or an escaped bird.
One of the most frequent forms to turn up in apparently wild circumstances in the UK is the nominate form hutchinsii, Richardson's Canada Goose, and this seems to be the form shown in the photos below.
David Sibley has written a useful article on the identification of Canada Geese.