Voyager and Thomas cook
If you already pay into fixed contract for A330 availability and flying hours (as the MOD does) then the only cost is fuel and any displaced activity. Leasing a smaller aircraft would be much more expensive, even taking savings in fuel and landing charges into account. These movements were probably planned in advance (notwithstanding the slightly early return!) but in any case there's no need to worry about expenses incurred by short-notice re-tasking of airframes; military passengers can be ordered to sleep at the airhead until a replacement arrives! Also, the press pack and their large amounts of equipment will all be charged for the privilege of being flown on HM aircraft.
Ministers said the conversion would save the taxpayer £775,000 a year in the cost of private charters, while the aircraft would still be available for its primary air-to-air refuelling role when it is not being used for VIP travel.....Government sources have said the cost of long-haul charter flights can be excessive because they are often arranged at short notice.In January 2015, the government spent more than £100,000 sending Mr Cameron to Saudi Arabia to pay his respects following the death of its king. The converted RAF Voyager A330 is expected to cost £2,000 an hour, compared to the current average cost of £6,700 an hour.
When I flew VVIP, I think it was Lockheed who suggested a fast bisjet to take Maggie from Dallas to LHR. It did. Just her, the VC10 carried the huge entourage of security, garden girls, MPs, press (who paid handsomely) & crew to look after all that (up to 19) etc. That idea was dropped. Anyway, the chartered stuff did not have anti-missile defence. The Ten did.