Commentary: PM’s admission has opened a Pandora’s Box

David Cameron has opened a Pandora’s Box. By reassuring today’s voters he will not go “on and on”, the Prime Minister has sacrificed some of his post-election authority.

In the Westminster bubble, there is a remorseless logic that forbids a leader from naming a retirement date. By ruling out a third term, Cameron has opened a question of who will take over. Since voters in 2020 will not elect a party whose leadership is unresolved, the power struggle must take place during the 2015 to 2020 parliament.

The next leader will expect to write his or her manifesto, so the sitting PM will have less say in the country’s long-term future. Moreover, the leadership rivals have a vested interest in forcing an earlier date for the handover so they can make plans for their re-election.

Mr Cameron named three possible successors, Osborne, May and Johnson. But other ambitious Tories, like Sajid Javid and Philip Hammond, want to be considered. Logically, they must start setting out their stalls as soon as this election is over. Inevitably, leadership speculation and positioning will dominate David Cameron’s last years and perhaps hasten his departure.

Downing Street points out that voters do not live in the Westminster bubble. Mr Cameron has done no harm to his re-election campaign. Many people will feel reassured by his candour and normality.

But Westminster is where Mr Cameron works and derives his authority. His re-entry to the real world now looks less distant than it did a day ago.