Bird call from near London park

I don't really have much helpful advice, as the closest thing I've heard to this is a Red Kite or some other birds of prey, but did you record in the presence of captive birds? I visit my grandparents in Wales occasionally and me and my grandpa go for a walk to different parks. In one park, there is an out of place enclosure with 5-10 budgies in it. They make familiar calls, and parrots also take up mimicry.

Anyway, that was my problem, but if this is a wild bird I suggest a bird of prey, most likely a typical London one like a Red Kite, Buzzard, Sparrowhawk or Peregrine. Alternatively, it could be a Tawny Owl calling, perhaps a fledgeling? Either way, I stand by my statement that it is a bird of prey, and I hope someone more experienced replies in case I've just embarrased myself.