"..even if just £1000 was generated it is more than the airport would have got if the aircraft hadn't used the facility."
If you have a fully-equipped airport handling many flights per day this would of course be true. However, if you have a handful of flights per day the economic analysis changes. You are having to provide fire and rescue services, air-traffic control, customs, security, ground-staff etc. etc. All of this is costing you money. The longer you are open for each day the more it costs you.
Consequently, the cost to you of providing facilities to accept that one flight far exceed the revenue you obtain from it. Far better to close down and divert the one flight somewhere else. Perhaps you could persuade the proper airports to pay you a finders fee every time you send them a plane.