Great Offices of State
The four posts are
The Chancellor, Foreign and Home Secretary are also appointed by the King. These are on the advice of the Prime Minister. Its more of a formality for the King to appoint as the decision is taken by the Prime Minister. This is the same for the other Cabinet Ministers. 
- McKie, David (28 March 2005). "Lord Callaghan". politics.guardian.co.uk. London: Guardian Unlimited. Archived from the original on 3 November 2007. Retrieved 10 June 2008.
He had held all four of the great offices of state
- Eason, Gary (27 March 2005). "Callaghan's great education debate". BBC News. Archived from the original on 15 January 2009. Retrieved 10 September 2010.