The PM’s announcement struck the wrong note on a number of fronts. It made it easy for Labour politician Douglas Alexander to attack him as “typically arrogant”. The U.K. population has historical form for disliking leaders who look like they are assuming the results of an election. The best-known example is probably the ‘Sheffield rally’ – when Neil Kinnock, then leader of the Labour Party (and now better-known as the father-in-law of the Danish Prime Minister Helle Thorning-Schmidt) appeared to enthusiastically celebrate an expected Labour victory, only to lose the election a week later.
Another is Cameron’s predecessor Tony Blair, who famously did not make it to the end of his third term after promising not to serve a fourth term – turning himself into a lame duck.
The prospect of an exit by Cameron also makes the speculation about who will be next more interesting. He named Theresa May, the Home Secretary; George Osborne, the Chancellor of the Exchequer; and popular Mayor of London Boris Johnson as potential successors. While these are the three most obvious candidates, by naming them he has effectively kick-started the campaign to be his successor, at least four years before he (presumably) wants it to start.