Geograph - photograph every grid square

London Biggin Hill Airport is located 14 miles south-southeast of Central London. The airport was formerly a Royal Air Force station RAF Biggin Hill, and a small enclave on the airport still retains that designation.
Biggin Hill is best known for its role during the Battle of Britain in the Second World War, when it served as one of the principal fighter bases protecting London and South East England from attack by German Luftwaffe bombers.
The airport has a CAA Ordinary Licence that allows flights for the public transport of passengers or for flying instruction. It specialises in general aviation, handling a range of traffic from private aviation to large business jets. It currently has no scheduled airline service, as flights using the airport are not permitted to carry fare-paying passengers.
Wikipedia: Link

A blue plaque is a permanent sign installed in a public place to commemorate a link between that location and a famous person or event, serving as a historical marker.

The world's first blue plaques were erected in London, England in the nineteenth century to mark the homes and workplaces of famous people.
The original blue plaque scheme started in the 1860s, is now run by English Heritage in London. It is believed to be the oldest such scheme in the world.
There are currently about 850 plaques in London.