LON is the Metropolitan London collective IATA code, not an airport collective.
Well in this case, same difference. IATA use "Metropolitan Area" codes like LON to group together facilities serving the same city - usually airports, but they can also include bus and rail stations, etc, where they have been allocated IATA codes.
But
AFAIK, the only codes that "belong" to LON in the IATA world are the 6 airports: LHR, LGW, STN, LCY, LTN, SEN.
LHR once had LAP applied.
I'm not so sure that LAP was ever the
IATA code for Heathrow. Certainly, in the 1960s, anyone in West London would recognise what was meant by L.A.P., but it's hard to believe that when IATA first introduced codes, they would squander 2 of the 3 available letters just to identify that it's an Airport.
Of course LAP is now the IATA code for La Paz (the Mexican one, not the Bolivian capital), but I don't know how long that's been allocated for.
Anyone have an early IATA Coding Manual in their archives ?