This is probably going to be more and more of a problem with the introduction of 'low cost airlines' seeking to fly into unknown and under used airports because it's ... lower cost than real (sorry, controlled airspace based) airports.
"London Coventry" and "London Doncaster" and "London Girona" (and others) will be demanding Class D airspace and start to push the prices up.
And then, the LCA's will be off to "London Gamston" and "London Catfoss" in order to get the price performance again.
I'm sure there was a reason why airlines used to fly into major established airports, with controlled airspace around them but like Boxer, I can't quite remember why ...