I'm glad I didn't rush off after the Chats fizzled away in the distance as a dark winged raptor soon grabbed my attention! I was initially getting broken views as it quartered on the skyline! It had to be a Marsh Harrier, even at distance, typical flight pattern and very long tail...
Shame about the white sky!! At this point I thought it was disappearing
There's a bit of sunlight artefact going on in this next image, the brown of the wing transformed to grey. However, that single grey 'new' tail feather is constant in all the images and that suggests it must be a male? A female would moult brown...