He's only ickle

Early November, appears at the same time as Greenland White-fronted Goose (Gwent's second record), unringed, undamaged wings, won't allow close approach; well that's the provenance sorted, now what the furcular is it?

Bill: small, short, stubby but not quite the ridiculous little triangular affair of minima.
Body size: very small, only seen in close association with UK feral Canada Goose (mostly canadensis? Referred to here as canadensis) although Greenland White-fronted Goose and Barnacle Goose also present. Body length appeared approximately two thirds of canadensis but much less in bulk (you might get three to every one canadensis; or, to put it another way, if a canadensis is 3 hours at Gas mark 6, then this bird would only be 1.5 hrs). Whilst not seen alongside one another, it seemed slightly smaller than Barnacle.
Neck: quite thick and, at all times, very short, even when extended during pre-flight anxiety behaviour.

Overall colour: dark, upperpart base colour a shade or two darker than canadensis; underparts very dark similar to canadensis upperparts, pretty concolouress across breast and belly, darker on lower neck, contrasting strongly with white collar, and regular pale and sparse blackish barring on flanks. Also a slight brassy sheen to the breast. Vent undertail and uppertail white. Tail blackish.
White 'cheeks': quite extensive and, though thinning slightly, still broad and square-ended at top.
Collar: clean white, quite deep on fore-neck thinning, and petering out, on sides.
Black chin stripe: lacking, although perhaps a slight 'dent' of black below the bill (maybe).
Voice: not heard (yet)
Structure: proportionately narrow in 'arm' and 'hand', quite a pointed wingtip; horizontal carriage; steep forehead and square head shape.

Structurally good (great?) for hutchinsii but really dark-breasted. Anyone got a photo of Hanson's 'baffinensis'?

See here for discussion and photos of the recent (near identical) bird at CVL, Blagdon Lake and Torr Reservoir (co-travellers or co-escapees?); and see here, and the references therein, for a good starting point to a white-cheeked goose inspired mental disorder.