Raptor help wanted!

Ok! What's this? I was driving towards Potter Heigham, just past the Oby turnoff, when I saw this large raptor in a cereal field right by the road. By the time I managed to turn around and return, it was flying away, gliding on flat wings and looking like one of the slim-winged Harriers... On the ground, it was very peachy, with a distinctly foxy cap. No pale rump, so it's probably a Marsh Harrier: but it just didn't 'feel' like one!