Looking for lunch

It's amazing the things you see on a dog walk. I didn't have time to compose this photo because just as I was getting ready Henry (my dog) decided to slip his collar and come to see what I was up to. This bird is not too keen on dogs and I think it put it off hunting for lunch.

Does anyone know what it is? I thought he said it was a Harris Hawk but I can't find this in the bird books. I must have misheard.