On face value this seems a strange arrangement, surely this opens up the whole problem of "what about me" from other airlines and indeed other airports!
The bribe has been paid to keep the UA going, in the meantime what happens the cash that Aldergrove will make on the back of it? If these flights are running with high load factors then that is a lot of people parking cars, buying items within the airport etc. Will there be some sort of clawback in order to try and mitigate some of the cash?
As has been mentioned, well done to the United commercial dept!