I once saw the HEMS Dauphin in the street outside Charing Cross Hospital, and if he had six feet of clearance from three lamp posts I'd be surprised.
An acquaintance in Richmond has had his garden scouted out by the Air Ambulance people as an emergency landing site. Personally I'd be hard put to park my bike in it, and it makes Cavendish Square look like the Gobi.
Good to know these chaps will fly through the eye of a needle when we need them.