MBJ,
Flying a single engine helicopter over the city of London is unsafe? What do you predicate that statement upon? Is there something about the strength of gravity or something that makes London an unsafe area to fly over?
Someone will try to tell us that a safe landing due to an engine failure is not a certain thing. The same people ignore Lorry-Car crashes, forget buses run over pedestrians, bricks fall off facades and muggers will stab you.
Why is the risk of a helicopter landing in your back garden any more a risk than all the other things that can happen to you?