Taxi
Single engined helicopters have to follow the
Heli Routes, which are strictly enforced by ATC. The routes are designed so that in the event of a failure, the pilot can always auto-rotate into an area big enough to land safeley - this includes the river Thames through central London. The lowest point on the Heli Routes is a short stretch over Kew (750' - to deconflict LHR traffic on finals for 27); the others are 1,000' or higher. I'd be very surprised if you saw many SE machines hovering at 1,000' on the Heli Routes.