During the early '70s I used to volunteer for the St Johns Air Ambulance Wing. This teamed light twin pilot/owners with commercial pilots to deliver live kidneys for transplant. On one occasion we were met by the police at Booker (WAP) in the middle of the night who opened up the airfield for us and parked a police car with headlights on at the end of the runway to aim at so that we could take off in the dark and position into LHR to collect two kidneys which were then flown on to AMS and Tirstrup for delivery. Another nighttime flight was again from Booker to ORY and BFS via Lee on Solent after radio failure! The airfield light beacon was used for identification.
I also during that period used to fly for an air taxi outfit based at Fairoaks and flights into and out of LHR and LGW were carried out using PA30 and PA23 aircraft. LHR used to have it's own light beacon situated near where the Hatton Cross tube station now is. I suspect these types of flight had all finished by the late '70s.