This may be a dumb question/observation, but assuming the probability that he was "scud running" towards a diversion, would he not have followed the Thames (that is one/the heli route, I believe)?
Forgive my ignorance of heli ops, but as far as I am aware there are no protruding obstacles emanating from directly above the Thames, other than bridges, had he remained above the centre of the river.
Or maybe the approach into the landing spot caused him to leave the security of such a routing?