Hold a great office of state other than PM in a Government that loses an election.
Remember from my last post, that the following leaders of the opposition have become Prime Minister since the war:
Attlee, Churchill, Wilson, Heath, Wilson again, Thatcher, Blair.
Churchill and Wilson the second time had obviously been Prime Minister before. But none of Attlee, Heath, Wilson the first time, Thatcher or Blair had served as Home Secretary, Chancellor, or Foreign Secretary previously.
Bad news for Miliband and Jacquy Smith and Alistair Darling if Labour lose the next election.