As the Exec Jets are squeezed away from London, airports situated close too, and feeding into London, can make more money from these movements, than from scheduled flights.
Folk on here seem to think that millions of passengers makes huge profits? I quote the Luton Airport CX from 1997. Luton made £1.75m clear profit from Exec flights. For this type of operation, you need a runway, and a place to board/de-plane in privacy.
My guess is that within the next 10 years, Cranfield will become the 'Farnborough' of North London, as slots become finite. Do a search on the plans of the University? Spending a little cash in airport upgrades, can yield untold profits. CAT1 both ends/CAT1 lighting both ends/Radar (The expensive bit!)
Staverton could achieve the same, albeit a bit further from London.