Very much a possible! But thought should mention.
Seen for less than 10 seconds. Very sleek looking raptor. General all dark, but with Clear 2 tone wing effect. Redish brown of forwing, dark brown black, primary and secondaries.
All in all intermediary appearance between marsh harrier and red kite in shape and colouration.
Flying low and fast over the pill, but only picked up, just before disappearing over hedge and not seen again.
No way could claim with any certainty, but was unusual enough that felt should mention.
Worth keeping eye out!