Since they would not approve a small airport terminal
wrong!
Warwick dc granted planning permission for a passenger terminal for 1 million passengers a year. The airport built it but has subsequently (perhaps unwisely) converted it to a business executive facility. The bigger 2 million passenger facility was rejected by planning inspectorate, call in and the high court.
Most of the airport land is in fact Green Belt land, and if/when it ceases to be operational airport, redevelopment of the land is by no means a planning formality.