The Rules of the Air Regulations and the Air Navigation (Restriction of Flying) (Specified Area) Regulations govern flight by helicopters over London. The former regulations specify the minimum height at which a helicopter may operate, the latter regulations prohibit single engine helicopters from the central area of London below such a height as would enable them to alight clear of that area in the event of an engine failure.
Helicopters are required to follow published routes over London subject to an air traffic control clearance. The routes, detailed in the UK Aeronautical Information Publication published by the CAA, are designed to provide maximum safety in respect of single engine helicopter traffic by avoiding built-up areas as much as possible. Twin engine helicopters, such as those operated by the emergency services, may be cleared to fly outside those routes according to their specific requirements and the Rules of the Air.
In addition, an aircraft flying in accordance with the terms of a police air operator's certificate (PAOC) is exempt from certain parts of the Rules of the Air Regulations, including the low-flying rule, if the aircraft is flown in accordance with the Police Air Operations Manual (CAP 612), published by the Civil Aviation Authority (www.caa.co.uk). In London, the Metropolitan police and the Surrey police have been granted PAOCs and may be permitted to hover above particular locations depending on the operational requirement.