London's air ambulance can reach anywhere inside the M25 within 12 minutes, travelling at 160mph. It is based at the Royal London Hospital, Whitechapel, in the east end of the capital, where a helipad allows the McDonnell Douglas MD 902 Explorer aircraft to land on the roof.
But fields or parkland allow it to reach any of the capital's hospital. It has a crew of two pilots and room for three medics and a patient.
The service costs almost £2m a year to run - paid for by mainly charitable donations. It flies more than a thousand missions a year, dealing with mainly road traffic and falls from heigh accidents.