The fortune is in the capital value of the aircraft. 65 BBJs/GVs/Falcons/Global Expresses and Challengers probably works out at about US$1bn on the apron. The average landing and navigation charge at LTN is probably between £200-500??, then the income would be between £13,000 to £30,000 - small potatoes really.
Still if they've got the slots which LHR hasn't then that's where the posh brigade will go.
A