The little hybrid goose cannot be a cross between an Anser and a Branta species, as these generally have a mainly dark tail (and also often darker bills or bills with black blotches). This means with that brightly coloured bill and legs and a typical Anser geese tail it has to be a cross between two anser species. It shows a clear indication of Ross or Snow goose parentage with the white-rimmed tertials and secondaries. As the bill is very small, I´d favour Ross goose as one parent. The other then should also be a small-billed species, probably with a pink bill also. Lesser whitefront seems to fit here best, so the most likely explanation would be Ross goose x Lesser whitefronted goose."
If the person who added this comment reads this post, I would be grateful for your opinion of the hybrids shown in the other two photos, both from Whitlingham. Bird 4 looks similar to a bird seen at Swanton Morley by Dave Appleton (possible Lesser White-fronted x Barnacle) whilst the bird in photo 5 has a similar wing pattern to the first hybrid but a larger bill and overall size, perhaps Ross' Goose x Greylag? Any comments most welcome.