Hi Omar, I think the exposure was so far out that I've lost any detail on the bird. I wish it had been a bit closer, or maybe if I'd just used my binoculars more instead of relying on the camera. When I first saw it with the naked eye I thought it was a swift but then it diving at the meadow pipits. My next thought was hobby but it was gone before I could get decent views of it. I wish I was more familiar with the two species (hobby/merlin) I know more experienced birders would have id'd it from it's jizz alone.
I am not happy with Kestrel as I agree with Omar that this bird does not have any brownish hue but looks steel-grey which seems not to be an artefact, thus my idea of Sparrowhawk, but again I agree with Omar that this bird looks falconish.
I got this picture from a friend, namely Claude Dording yesterday and it nicely shows that Hobby sometimes can look veryyyyy long tailed.
This is due to the fact that their slim body is fusing with the tail and you can hardly see where the tail starts and the body ends, even less so in the OP pictures. Combined with slim wings, even at the base this could well give the OP's shape.
So imho Hobby fits best the hunting skills and the shape.
Omar's lightened photo certainly looks more like a Hobby. I wouldn't expect the streaking on the underparts of a Kestrel to look quite so bold and as Tom points out, Hobby can look 'long tailed' at times. The behaviour and the fact Damian initially thought it was a Swift seem better for Hobby, plus the fact they are a lot more widespread around north west England than people think.
Thank you very much for all the replies. When I initially put the picture on, I'd hoped there was enough there for someone to differentiate between either hobby or merlin - I wasn't really expecting it to be a kestrel but was prepared to accept that it was just a kestrel behaving differently to ones I've seen before.
I'd like to think that even with the brief views I had, I would have known if it was a kestrel - hopefully anyway! The only time I've seen hobby before I thought it looked swift-like and my initial thought when seeing this bird was exactly the same. If the pictures could possibly be a hobby then I think that is the most likely explanation although I suppose I'll never be sure. Hopefully when I've seen a few more of them, I'll be able to look back at this one with more certainty. Thanks again, Damian.