There has always been planned QEC VIP kit for the Voyager.
Far less cost then chartering airline BA/VS 747/777 as has been used for royal flights in the past. Gov. have been chartering private 767s at great cost recently for ministerial trips.
The civvy AirTanker cabin crew could easily attend an airline First Class cabin service course (VS have A330) The cabin service required for Royal/Ministerial flights a bit beyond the RAF Voyager cabin crew training for trooping flights.