Asked if he regretted stating his intent not to continue beyond 2020 – which critics have warned undermines his authority and distracts from the Tory campaign for re-election on 7 May – he said people should “just focus on the issue” of who they wanted running the country.
And he dismissed calls for him to set out exactly how the Tory leadership succession would work as “endless games of political processes” that the public would not be interested in.
Mr Cameron was grilled over his surprise statement, in a BBC interview broadcast on Monday night, after addressing an Age UK summit in London.
He said: “I am taking absolutely nothing for granted. My entire focus is on the next 44 days and the general election, which will decide which team runs this country for the next five years.
“I want that to be me and my team but the alternative is it is Ed Miliband and his team, and that is the focus that I have in the days ahead.
“What I did in my kitchen is I gave a very straight answer to a very straight question and I think that people will understand that – that saying you want to serve a full second term for a full five years is a very reasonable, sensible thing to say.”
Mr Cameron shocked Westminster when he revealed he would serve a full second term if he remained Prime Minister after the election but would not “go for a third term” in 2020.
He fuelled speculation about a leadership battle to come by naming three of his senior colleagues – Home Secretary Theresa May, Chancellor George Osborne and London mayor Boris Johnson – as possible successors.
Aides later briefed that no decisions had been made on whether Mr Cameron would fight the 2020 election or hand over to a successor in advance, saying: “We will cross that bridge when we come to it.”
Shadow chancellor Ed Balls described the Prime Minister as “spectacularly self-indulgent, presumptuous and arrogant” for giving the impression of taking victory for granted when the country goes to the polls in May.
Former Downing Street director of communications Alastair Campbell said the seemingly off-the-cuff remark was “a potential disaster” for the Tories, who could find their election campaign dominated by speculation over a future leader.
Former Conservative Cabinet minister Michael Portillo described Mr Cameron’s announcement as “bizarre”.
Mr Portillo said: “I think it is bizarre and it has occupied the last day’s news. It may even occupy another day’s news.”
He added: “When you play chess you have to consider the next two moves, and I don’t think he did. There is no point setting off on this wild goose chase in the middle of an election campaign.”
During his address to older voters, Mr Cameron raised eyebrows by talking of his political “epitaph”.
“I’ve got to be honest with you,” he said. “I don’t want my political epitaph to be that I balanced the books and cleared up the mess I inherited.
“I am here today because I want a different kind of Britain – a country with the right values, a country where reward follows effort, where you get out when you put in.”
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