PM rules out serving three terms
David Cameron has ruled out a third term as Prime Minister if he remains in 10 Downing Street after the May 7 general election.
Mr Cameron said he will serve for a full second term - which could last until 2020 - if elected, but added: "Terms are like shredded wheat - two are wonderful but three might just be too many."
He named three of his senior colleagues - Home Secretary Theresa May, Chancellor George Osborne and London mayor Boris Johnson - as possible replacements as Conservative leader when he stands down.
Labour accused the PM of "arrogance" and taking voters for granted. But Downing Street sources insisted that Mr Cameron was focused on the need to win the election in six weeks' time.
Although the PM had made clear he would not serve a full third term, no decision had been made on whether he would fight another election or hand over to a successor before the poll.
"We will cross that bridge when we come to it," said a Downing Street source.
"He is clear that we need to win the election in 2015 first. As the Prime Minister has said a number of times, he fully intends to serve a full second term if he wins that election."
In an interview with BBC News, Mr Cameron was directly asked if he would "go for a third term" if he remained PM after the election.
He replied: "No, I think I'm standing for a full second term."
And he added: "I'm not saying all prime ministers necessarily definitely go mad, or even go mad at the same rate, but I feel I've got more to bring to this job, the job is half done, the economy's turned round, the deficit is half down and I want to finish the job."
He added: "There definitely comes a time where a fresh pair of eyes and fresh leadership would be good, and the Conservative Party has got some great people coming up: the Theresa Mays, and the George Osbornes, and the Boris Johnsons. You know, there's plenty of talent there. I'm surrounded by very good people. The third term is not something I'm contemplating."
Mr Cameron said political leaders should never regard themselves as "indispensable".
"Countries, like big organisations, benefit from strong and consistent leadership but there comes a time when you want a fresh pair of eyes and a fresh agenda," he said.
"Certain things that other people would bring, and so you must never think that you're indispensable. However mad you go in this job.
"I've said I'll stand for a full second term, but I think after that it will be time for new leadership. Terms are like shredded wheat - two are wonderful but three might just be too many."
Labour campaign strategy chairman Douglas Alexander said: "The Tories are taking the British public for granted.
"It is typically arrogant of David Cameron to presume a third Tory term in 2020 before the British public have been given the chance to have their say in this election. In the UK it is for the British people and not the Prime Minister to decide who stays in power. "
"Instead of focusing on themselves, it is time we had a Government focused on the needs of working families. Another term of this Government would mean working people worse off and the NHS under threat because of their extreme spending plans. We need a better plan for a better future. We need a Labour government."
Mr Cameron's announcement caused surprise in Westminster, where Tony Blair's 2004 announcement that he would stand down before the end of a third term was widely seem as one of his biggest political mistakes.
The move did not end pressure on Mr Blair to announce the exact date of his departure, and he was eventually forced out earlier than planned. Mr Cameron's announcement is all the more surprising because he has not faced the same pressure as Mr Blair did to hand over to a successor.
His pledge to serve a full second term will raise some eyebrows in Westminster, where some had expected him to be forced to bring a close to his premiership following his planned 2017 referendum on EU membership, whatever the result.
In the latest of a series of BBC profiles of the private sides of party leaders, Mr Cameron was seen cheering on son Elwen's football team from the sidelines, shopping in the local butcher's and preparing food in the kitchen of his Oxfordshire home.
Mr Cameron paid tribute to his wife Samantha for keeping him "sane" in Downing Street, and revealed she will be playing a role in the Conservative election campaign.
"The fact that we do different things helps actually," he said.
"She keeps me sane because she's one of the most organised people that I've ever come across, so home life, the children's life, everything is just brilliantly organised.
"Otherwise you wouldn't get this family time - unless you're really well organised everything would be blown off course, you wouldn't get the chance. She's amazing like that.
"But we'll be out on the campaign trail because we're passionate about this election and what comes next. She is right behind me and what I'm trying to do."
He added: "She will be out there campaigning with me some of the time, she will be out there on her own supporting Conservative candidates some of the time, but she has also got a job and we've got three children."
Mrs Cameron made clear she hopes her husband will remain at Number 10, telling the BBC: "He is definitely in my mind the best man for the job."
She added: "I hope me and the children help him keep things in perspective, keep him grounded, help him pace himself over the next eight weeks."
Mr Johnson - whose decision to seek re-election to the Commons at May's election has fuelled talk of his ambitions for the top job - said another five years of Mr Cameron in Downing Street was "exactly what we need" and sought to play down leadership speculation.
"I think it frankly is people making a fuss about nothing," he told Sky News outside his London home.
"What the Prime Minister is saying is that he is going to serve on as Prime Minister and leader of this country until 2020, which is, by the way, exactly what we need to entrench the great economic recovery that we are seeing and ensure the future of this city, the city that I am mayor of, and of the whole of the UK.
"Five years is a very long time, and I'm sure he'll do a fantastic job in that period."
Asked it was flattering to be named by Mr Cameron as a potential successor, he responded: "The next leader of the Tory party is probably a babe unborn."
"Kids grow up fast these days, folks," he quipped.
A Liberal Democrat spokesman said: "It's incredibly presumptuous of David Cameron to be worrying about a third term as Prime Minister weeks before the general election.
"He should spend a bit more time considering how he can possibly justify to voters the Tories' dangerous plans to cut public services than agonising over his own long-term legacy."
Tory chief whip Michael Gove said he "wasn't surprised" by the declaration - and suggested it was the natural consequence of moving to fixed-term parliaments.
He drew parallels with the US presidential system, suggesting a contest to choose Mr Cameron's successor could take place while he remained in Number 10 right up to the general election.
Asked if Mr Cameron would "stand and run" in 2020, Mr Gove told Newsnight: "No, because he is going to be Prime Minister for five years in the next term.
"If you were having a presidential election in the United States of America and you had had a president who had had one successful term, it would be natural for that president to seek a second term in order to finish the job and then stand down and hand on to a talented successor.
"So the Prime Minister, when asked a direct question, gave an honest reply, and an honest reply which actually reflects the new political reality of a world of fixed-term parliaments."
"The plan is to make sure that we have David Cameron running this country for the next five years and to make sure that we have a choice at the election after that between whoever the Conservative leader is and whoever the Conservative leader is."
Barack Obama , Bill Clinton and Ronald Reagan had all been "strong executive leaders throughout second term" in the US, he said, where presidents are limited to two four-year terms.
Asked if the announcement was planned, Mr Gove told the programme: "As far as I was concerned, it was a statement of the bleeding obvious. I wasn't surprised by the Prime Minister saying it."
And he sought to present it as a positive for the party at the general election.
"One of the reasons that it will help us win is that it reinforces in everyone's mind the fact that we have, as our Prime Minister, a normal, sane, decent guy who is in politics for the right reasons, who when he is asked a direct question gives and honest answer and when he seeks public office does it because he wants to finish the job to make sure our economic recovery is sustained.
"He is not in it for glory, ego or wealth; he is in it because he believes that has another five years to give and he has seen other leaders - including David Cameron sadly - cling into office too long and spoil the early promise."
It contrasted with predecessors - including Margaret Thatcher - "whom you've had to prise out of Downing Street, their fingernails there in the door jamb", he added.