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Niknak....
I'm sure the PC12 Driver or (laughs!) his operations department are told where to go to drop of X and pick up Y etc...As the owner or customer I don't necessarily care what inconvenience I'm causing if it saves me time and/or money. I suppose the surroundings don't really matter to me either, as the kind of people who are using these aircraft are more than likely 'working on the move' and probably wouldn't notice.
Me thinks the owners of Elstree are aware of it's locale and the benefits that it brings...therefore aren't really up for spending money when there is no reason to.
As Fried Chicken points out, the number and variety of types operating into Denham, Elstree, Fairoaks......etc.. is only going to get bigger and the congestion worse.