Help identifying this bird (London, UK)

I'd appreciate any help in identifying this bird that is visiting my garden in NE London. It loves Nyger seeds as well as fat balls and standard seed mix, and is a good inch longer than the goldfinches I have seen it with.

I initially thought it might be a greenfinch with a pigmentation problem, but I honestly don't know. It does have a pronounced yellowish underbelly which isn't very visible here.

No matter what it is, I really like it !!

Thanks in advance