Hi all,
As with Peter, my gut reaction, on seeing the apparent head contrast, was Peregrine, but it soon became apparent that quite a few things were wrong for that species: pretty much everything he wrote about tail length compared to the total body length, narrow tail base and so on, also the apparent dark subterminal band seems perhaps a bit too broad for Peregrine also?
The head does seem a bit too dark for a Merlin, but I have seen birds (aesalon/subaesalon in Ireland, not seen enough columbarius often enough to have the same level of experience with them) which, when seen in certain lights/at certain angles, have appeared, however momentarily, to be 'hooded'. In particular, I recall a female type (most likely a juvenile, but it flew through low and quickly) at Clonea, Co. Waterford in January 2012 that, after flying low over the beach, then banked a bit as if flying out to sea and, for a moment, had we not seen it at close range first and had it not been January, the bird could have given a misleading impression of being a Eurasian Hobby, such was the apparent head pattern! Now, I am not saying the bird in the image has to be a Merlin, the image is very poor and grainy and fine detail would be extremely compromised, but it certainly seems possible that it was. The structure would seem to fit, anyway.
Regards,
Harry