Actually Paul, I find these photos very informative, and I just felt the first photos appeared, in two shots at least, to show a bird with too extensive and too "gleaming white" a rump to be Asian - then the second set looked like Asian. It seems now that both species were present.
As I said these shots are much clearer and I think I would have gone for Asian for the first and then wondered about the others, favouring Northern on the basis of the last two and the black-white distribution on the head, but concerned about the colour of the underwing coverts in shots two and three - though as you say, Paul, they're not black. The depth of the tail-fork does not appear to be very helpful as an indicator.
I take it the last shot is indicative of moult being underway and the bird being likely to have been subject only to relatively short-distance movement.
Is it lagopodum?
Again I think scrutiny of the occasional small winter flocks of House Martins we get may lead to more Northerns being seen.
Mike Turnbull
