Tom I am copying you! I came across this eagle in London last year and apart from this couple no-one batted an eyelid. apparently it is flown there regularly to clear the pigeons and it works. The handler was by a van over on the other side of the lions (lion statue that is!) way out of sight. May be the same bird you saw.
I think we need to do some more theme days, since we seem to be doing them anyway!