I'm 99% (ish) certain it is a Marsh Harrier
Agree its a marsh harrier but as Rob says colour looks wrong.
Pale underwings like that is male. Dark with light head is female. Juveniles quite like females but with light underwings
So, male but colours wrong or juvenile but head's wrong. Could either be an exposure problem on a male I guess or I'm not sure what stages the juveniles go through as they mature.