"People have mentioned about the wisdom of buying/building houses near airports in this thread. People have also mentioned about the proximity of a school and hospital to Biggin. Presumably both of these were also built after WW1 or whenever it was that biggin opened?"
"We were here first" is not enshrined as a principle of settling such things, though. If having an airport nearby was shown to be dangerous to nearby houses (of course it isn't) then moving the airport or changing the way it operates would be the less disruptive option. The same goes for chemical plants and other such things. When you do a risk assessment you don't take into account when the various parties arrived relative to the risk.
In no rational world is a nearby airport a significant threat against the background danger level we all experience just by being alive. Win the argument that way. "These people chose to be near the risk" won't... fly.