For the purposes of this answer, the Prime Minister’s Office is part of the Cabinet Office.
The Cabinet Office does not hold a breakdown of the information required since June 2007.
Cabinet Office policy requires officials to use the most cost effective class of air travel appropriate to the business need which takes account of the level of work that needs to be done during the flight and the importance of minimising fatigue. Standard class should normally be used but where the circumstances are justified, including longer flights, officials may travel in a higher class. Seats may be up-graded to a higher class where this does not involve additional cost. All travel is undertaken in accordance with the requirements of the civil service management code and the ministerial code.