"VIP" aircraft.
Many of the comments on this thread take me back to 1979 when the RAAF acquired the last two Qantas B707-338's. As a Flight Engineer on the aircraft I, and the rest of the crew, often had to fend off criticism by ill-informed members of the public. They were critical of PM Malcolm Fraser and "his VIP jets". Not only the public, but the Opposition Leader of the era, Mr Bob Hawke, declared he "would sell the B707's". Not only did Mr Hawke not sell the two ex Qantas B707's, his government acquired another five. Eventually four of the fleet were converted to aerial refuellers, but retained their pax/cargo capability.
The reality was that a very small percentage of our tasking was for "VIP" operations, as a look through my log book would clearly show. The aircraft which replaced the B707's are A330's which are multi-role capable and would, if required I am sure, be used to transport VIP's.
As in Australia, the ill-informed in Britian will bleat about any expenditure which they perceive to be "political perks". Look at the big picture folks, your Executive Government Ministers deserve to be transported in safety by your RAF, whenever required.