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Didn't look right, then I looked for juvenile dunnock pictures and it fits the bill!
I think it probably is a bird born this year, as the iris does not look very chestnutty, like an adult (young birds' irises are more grey). The rest of the plumage is effectively adult, though, and lacks the pale feather tips of a juvenile. You cannot really tell the difference between an adult and a young bird from its plumage, at this time of year.
My Flickr photos...
Lat/Lng: 51.9, -0.2
OS grid ref: TL3024