In September 2020, photographs of two unusual looking birds were sent to me.The one above was photographed in a garden in Lochranza and the one below at the Wine Port in Strabane. In both cases the photographers were not sure what these birds were. The first one was with Goldfinches and the second one was with Chaffinches. That was a clue to their identity. The first was an unusual Goldfinch and the second an unusual Chaffinch. Both had unusual amounts of white feathers. Birds like this are said to be leucistic. They are not a separate species just individual birds with this condition. Sometimes the condition makes the plumage entirely white and sometimes there are varying sizes of patches of white, as in these photographs. It is thought to happen when the plumage lacks melanin pigment due to the cells responsible for making melanin being absent.
There is much more information on this link Leucism & albinism | BTO - British Trust for Ornithology https://www.bto.org/our-science/projects/gbw/gardens-wildlife/garden-birds/behaviour/plumage/leucism and within this link there is a place where these unusual birds can be reported.