Which bird makes this sound? Any ideas anyone?

Does anyone know which bird this is? Heard often in East Midland town garden (lots of big trees) this summer. (sorry about the quality of the recording)

It sounds a bit like a honking or soft "awk awk awk" - definitely not a sqwark - softer and more melodic,  It seems to perch high up  in tall trees and, from what we can see, might be a large dark feathered bird....