I believe (from its behaviour) that this is a young robin in its first red suit.
It was sitting on a low branch in shady woodland with a bit of a breeze blowing through ruffling its feathers. In fact it was so dim that I was down to 1/20th sec exposure (hand held) without realising it. I mistook the flashing orange icon of camera shake for a warning of a low battery (which I knew was on).
All's well that ends well though and at least I got my blip.
Update 2 days later.
I am updating my interpretation of this image and no longer think it is a young bird (though it may still be so).
I went back to the same location and this same robin put in an appearance and took some crushed peanuts that I put out for it just a few feet in front of me. The reason I thought it was young was because of the uncoordinated way that it landed and fluttered. It is now obvious that that was because it has a broken or deformed leg and has to land on a single leg. Its trust in humans suggests it is an experienced bird rather than a juvenile.