I was trying to work that out myself, and I'm British and a bit of a bird-watcher. "black-headed, white-backed shape with the axe-like beak" - it's cawing and generally acting like a member of the crow family, but it has a white back. That would fit a magpie (sort of crow family but not quite), but they don't caw. Baffled.
http://www.rspb.org.uk/wildlife/birdguide/families/crows.aspx
http://www.rspb.org.uk/wildlife/birdguide/name/m/magpie/