This ID was not immediately obvious, and even still you could argue against it. If it is correct there are multiple modifications from the original image, but there is precedent for that (see the lapwing, for example, or the goosander).
The chaffinch appears above George's head. Below is the bird from the red collage, the green collage, and the chaffinch (flipped) from Coloured Figures of the Birds of the British Islands. (Confusingly, George and his bird are depicted in the contrasting colour in each collage, so the left image is from the red collage even though George is green, and vice versa).
Below I have pasted the chaffinch illustration on top of George's bird and shown the combination at different opacities. Further down I have the 0% and 100% illustrations with circles indicating points of comparison. I hope this helps explain why I think this is the right bird, but I'd love to hear your thoughts.
