Mainly, people in London use 5 airports. It shows how often they usually use aircrafts, considering that London is just 28th largest city in the world, and few cities of the top 28 cities have more than 5 airports.
If protesters want to resisit expansion plan of Heathrow airport, they should propose alternative transportation to deal with saturated demand for the airport.
For, example, diversifying destinations of Eurostar trains and promoting building bullet trains from England to Scotland would be effective.