The prime minister has said he will stay on for a full third term if he wins the next general election.

Tony Blair's announcement on Thursday night, coupled with news that he will undergo further treatment for a heart condition, is designed to end speculation about his future.

The move follows suggestions earlier this year that he was on the point of stepping down in favour of Gordon Brown.

Speaking to the BBC following the conclusion of the Labour conference and the close of polls in the Hartlepool by-election, Blair set out the scale of his ambitions to remain in office.

But he said he would not fight a fourth general election, and would stand down at the end of the next parliament.

"The decision as to who is the prime minister of the country is the decision of the British people - they're the boss," he said.

"But if I am elected I would serve a full third term. I do not want to serve a fourth term.

"I don't think the British people would want a prime minister to go on that long but I think it's sensible to make plain my intention now."

He added: "If you put yourself forward, you've got to put yourself forward for the full term."

Blair said he was still determined to stay in office, reaffirming his commitment to oversee further reforms in areas such as health and education.

"The reason I want to stay on is to see the job through," he said. "I've begun it, I want to see it through."

The prime minister added he still had "something to give and contribute to the country".

"The point is, I still feel a sense of passion and conviction about what I do."

The Labour leader added that the party's rules mean a ballot to decide on his replacement "can be done reasonably quickly", allowing him to step down shortly before the general election.

He also said that the door was still open for the chancellor to move from 11 Downing Street to Number 10.

"I don't think it rules Gordon out in any shape or form at all - he'd be younger than many prime ministers have been if he took over at the end of a third term," Blair said.

However, with a leadership handover up to five years away, speculation will focus on whether the younger Alan Milburn is now favourite to succeed Blair.

Meanwhile, it also emerged that the Blairs have brought a multi-million pound house in London, apparently in preparation for the prime minister's retirement.