Unknown bird of prey

I’ve just seen what I think is a bird of prey but can’t find it in my book.

Its white bodied & winged underneath, but with black wing tips covering about a third of the wing on the top side. About the size body wise of a kite but wing size a lot smaller.

i think that’s accurate ; it’s very lively diving up and down on the fields making a whooping sort of sound, but hard to get a good look at. At rest, on the ground, from afar but sadly without my glasses it’s quite greyish.

i live in East Yorkshire.