When is a Chaffinch not a Chaffinch? Help!!

[len1978]

My Dad has a visitor under his bird table at work that is the same dimensions as a Chaffinch with the same beak but it is all one colour (light toffee) the only markings it has are 3 black stripes on the top of it's tail that go straight across and appear to be the width of it's tail but could but cut off by the wings. He has so far been unable to get a picture of it although it is a regular visitor. It appears with other Chaffinches and has sat side by side with a female Chaffinch so he has been able to compare them. It is a ground feeder. Any suggestions would be gratefully received
Helen

[SimonP]

Possibly a Brambling, the migrants mix in with Chaffinch flocks over the winter. I've seen one in our back garden recently with a group of Chaffinches.