Typical red breasted adult robin...puffed out in the cold air!
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I think you are right about it being an adult. A bird born last year would have retained its juvenile tail feathers, which tend to be more pointed. Also it would have retained some pale-tipped coverts in the wing, but I cannot see any here.
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Yep....I did see a juvenile flying around...but I did not know it at the time.
It had dark stripey underparts which my collins reference book tells me is a classic sign of the juvenile.
To be honest, juveniles at this time of year look virtually identical to adults. It is just the points I mentioned above that differ (and maybe the colour of the inside of the upper mandible!!). If you saw a bird with dark stripey underparts (and assuming it did not have a red breast), then I suspect you were looking at a different species. A Dunnock, perhaps? If it was a red-breasted Robin, with dark stripey underparts, then that was probably just some staining or was wet feathers, which can give the impression of stripes on the white belly.
Lat/Lng: 51.1539, -2.4986
OS grid ref: ST652395
The location is an equine yard with a mixture of open fields for grazing, mature hedges, out-buildings and various trees (Pine, Oak, Horse Chesnut, Hawthorn, Apple etc.)