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

Listed buildings and structures are officially designated as being of special architectural, historical or cultural significance. There are over half a million listed structures in the United Kingdom, covered by around 375,000 listings.
Listed status is more commonly associated with buildings or groups of buildings, however it can cover many other structures, including bridges, headstones, steps, ponds, monuments, walls, phone boxes, wrecks, parks, and heritage sites, and in more recent times a road crossing (Abbey Road) and graffiti art (Banksy 'Spy-booth') have been included.

In England and Wales there are three main listing designations;
Grade I (2.5%) - exceptional interest, sometimes considered to be internationally important.
Grade II* (5.5%) - particularly important buildings of more than special interest.
Grade II (92%) - nationally important and of special interest.

There are also locally listed structures (at the discretion of local authorities) using A, B and C designations.

In Scotland three classifications are also used but the criteria are different. There are around 47,500 Listed buildings.
Category A (8%)- generally equivalent to Grade I and II* in England and Wales
Category B (51%)- this appears generally to cover the ground of Grade II, recognising national importance.
Category C (41%)- buildings of local importance, probably with some overlap with English Grade II.

In Northern Ireland the criteria are similar to Scotland, but the classifications are:
Grade A (2.3%)
Grade B+ (4.7%)
Grade B (93%)

Read more at Wikipedia Link