I'm sure this was a Marsh Harrier. It could have been a buzzard or Sparrow Hawk, but there is a black line going around the white of this bird of prey's head. A bit like a Lone Ranger or Tonto mask. However, I'm no expert and could be wrong. This hawk was in the fields across the road from my home. It was some distance and the 300mm lens captured it, though not as good as a more powerful lens.
If it is a Marsh Harrier, it would mean that the bird of prey is also using our fields as a hunting ground. This is exciting as birds of prey numbers are increasing rapidly in the Fenland.