My area isn’t known for hen harriers but I saw a bird of prey that looked like one. It was dancing through the air, wings in a “V” shape. Back and belly were white and wing tips were dark. Smaller than a buzzard. What else could it have been?

Male Marsh Harrier maybe? They fly in that shallow V you mention and some males are very pale

I can see you live in the same area as I do, thank you for your reply. I have watched marsh harriers for several years but never seen one so white! I am trying to spot it again with my camera