Uk bird of prey eats fish?

I have just seen a "Buzzard sized" bird of prey swoop down and grab a fish out of the river Thames just south of Oxford. I was wondering what this could be and is this normal behaviour? I had a bit of a search online and I could not find a British bird of prey which eats fish save for the Osprey; I severely doubt it being an Osprey. Maybe I did not look hard enough, can anyone here clear this up for me?