Anyway I scooted over to "the long grass" at the Scrubs where the bird was rumoured to be lurking. Sure enough, it did not take long to spot a distant white splodge atop a bush, surrounded by a posse of West London's finest. An exhausing couple of hours ensured, during which time the skrike led me a merry dance around this surprisingly large "park". Rolling Prairies more like.
Eventually I realised that the best plan was to stake out a random bush and wait with my heavy camera for the bird to come to me. With good grace it did so just before my parking ticket ran out. A very handsome creature and what a treat to escape from the office for the last few hours of our Indian Summer sun.