Thought I would include this one because it shows the bullheaded appearance - a characteristic of this species.
No interactions present.
Looked at a few books as I am not very familiar with the redpolls, and was disappointed that descriptions and illustrations were often slightly different for the same species.
Can see that this one is generally pale enough to be an Arctic rather than a Mealy, less streaked and with a more tawny head. Didn't know what to make of the stripe above the eye, as this was one of the contradictory parts of the illustrations. Were there other things that helped you decide it was an Arctic? And how did you come down to Hornemann's rather than C. h. exilipes?
Had a quick look in Birdtrack and there are very few Arctic observations recorded over the last few years, so it is a good spot anyway.
The colouration and lightly streaked breast make it an arctic. The pale rump is another feature of arctic and I've added another image which shows this better.
As for being Hornemann's the size, very pale colour and ground feeding behaviour are all indicative of this sub-species.
I'm not surprised that you found the illustrations and descriptions in the books you looked at were often different - repolls (all currently recognised species and races) are very variable.
If you are interested in trying to get to grips with repoll identification it is worth seeking out some of the more in depth discussions there have been online (I can't give you any sites off hand I'm afraid).
Alternatively try and get hold of the identification paper in the February 2000 edition of British Birds, or read 'The Macmillan Birders Guide to European and Middle Eastern Birds' by A. Harris, H. Shirihai and D. Christie.
Looks like an Arctic to me, but then I've never managed to see one (they don't get down to Dorset very often).
Here's my favourite redpoll ID guide:
Still seems very difficult to me. Just have to accept that as one of our local birders used to say - that I can't tell a bee from a bull's foot!
Lat/Lng: 60.0, -1.3
OS grid ref: HU4429