Three key facts about David Cameron's departure

One down, two to go. One consequence of David Cameron’s announcement that he will not seek a third term as Prime Minister is that we are now less than five weeks away from his last pre-election television grilling. Last night’s encounter with Jeremy Paxman has probably changed little; neither Cameron nor Ed Miliband achieved a knock-out blow. I suspect, though, that the Prime Minister is relieved that he is approaching the end of this form of duel.

Meanwhile, the coming election is likely to provide enough facts for Michael Caine to update his trivia book, Not Many People Know That. Here are three, following Cameron’s statement about his own future:

1. He will be the youngest ex-Prime Minister since William Pitt. Tony Blair was 54 when he left Downing Street. David Cameron will be 53 if he remains in office until just before the 2020 election.

2. If he genuinely leaves at a time of his own choosing, he will be the first Prime Minister ever to leave voluntarily at the peak of his political and physical powers. Blair hoped to stay on until later in the 2005-2010 parliament, but in order to fend off Gordon Brown and his followers, was forced to announce in September 2006 that he would leave the following June.

Harold Wilson probably comes nearest to a voluntary departure. Most people were surprised when he stepped down in 1976. But it is clear that he knew his health, and especially his memory, were beginning to fail.

Otherwise every Prime Minister has departed from Downing Street following electoral defeat (eg Brown and John Major), party pressure (eg Blair and Margaret Thatcher), parliamentary set-backs (eg Neville Chamberlain and Robert Peel), ill-health (eg Harold Macmillan and Anthony Eden) or death (eg Lord Palmerston and Spencer Percival, the only PM to be assassinated).

3. If he wants to hand over as Conservative Party leader before the 2020 election but stay on as Prime Minister until the election is over, there is a precedent for splitting the two positions. When Chamberlain resigned as PM in May 1940, he remained party leader for almost five months; Winston Churchill did not become Conservative leader until October 1940.

Spain provides a more exact precedent. In October 2003, its centre-right Prime Minister, Jose Maria Aznar, announced he would stand down after the 2004 general election. The party Mariano Rajoy was to be his party’s post-election successor. Until three days before the election, their party seemed to be heading for victory. Then came the terrible bombing of a train in Madrid. Rajoy immediately blamed Basque separatists. Within hours it became clear that Islamic terrorists were responsible, Rajoy lost public support and the Socialists won the election.

That precedent, then, is stained with horror; even so, I see no reason in principle why Cameron should not remain PM until May 2020. Whether he wants to and, if he does, whether his party will let him, are of course another matter.