I think its a Montagu's male, but the underside isn't clear enough to be 100% on that. Looks like its carrying prey too, so nesting.
This is an adult male marsh harrier, because of the brown body and pale underwings with black only on the tips. The very long legs and long 'fingers' on the end of the wings are also good identification points. Males of the other three European harriers (hen, pallid, and Montagu's) all have much lighter bodies and a lot more black on the wing-tips, with male Montagu's especially having a lot more markings on the underwings than this individual.