Female Chaffinch, but not a juvenile; I don't think (but haven't checked) that the white wing-bars would be so well developed on a juvenile bird.
Thanks Colin. What threw me is that most of the images in the Collins Bird Guide show the more colourful male. A group of these birds visit my garden quite frequently but they are a bit skittish. Had a bit of luck the other day when I caught them unawares.