While considering the power of the Prime Minister I jotted down this brief list of Prime Ministerial departures since Neville Chamberlain in 1940. It does offer one perspective on where the power lies. While governments always leave office at the ballot box, Prime Ministers certainly do not, although not all of those who resigned were forced from office, Churchill and Macmillan for example resigned due to ill health. It is striking to compare this with US Presidents in same period, all but three of whom served full terms of office, the exceptions being Franklin Roosevelt who died in office, Kennedy who was assassinated and Nixon who resigned.
Chamberlain (Con) – resigned
Attlee (Lab) – election defeat
Churchill (Con)- resigned
Eden (Con) – resigned
Macmillan (Con) – resigned
Douglas-Home (Con) – election defeat
Wilson (Lab) – election defeat
Heath (Con) – election defeat
Wilson (Lab) – resigned
Callaghan (Lab) – election defeat
Thatcher (Con) – resigned
Major (Con) – election defeat
Blair (Lab) – resigned
Brown (Lab) – election defeat
Resigned/retired – 7 Defeated – 7