Tony Blair will step down as an MP at the next general election, according to his Labour Party agent.
The prime minister has said he will serve a full third term
John Burton, one of Mr Blair's closest friends and political allies, said: "He has spoken to me about it, and as far as I know he is not going to stand."
Mr Blair, MP for Sedgefield, has already said he will quit Number 10 after serving a full third term.
But Downing Street played down reports the premier had told friends he wanted a "clean break" with politics.
Mr Burton was credited with talent spotting Mr Blair ahead of the 1983 general election and has been his agent in Sedgefield ever since.
He told The Northern Echo: "Tony's said he is packing in as leader and he's not going to stay on the back benches - so I can't see him standing at the next election.
"He has spoken to me about it, and as far as I know he is not going to stand."
TIME ON THE BACK BENCHES
John Major - stayed in Commons four years after ousted as PM
Margaret Thatcher - one-and-half years on back benches after leaving No 10
James Callaghan - left Commons eight years after his stint in Downing Street
Harold Wilson - seven years in Commons after resigning premiership
Ted Heath - retired as MP 26 years after resigning as Tory leader
Alec Douglas-Home - stayed in Commons for 10 years after end of premiership, some of them as foreign secretary
Mr Burton said he could not see Mr Blair as a backbencher "in the Ted Heath" model.
"He has got more important things to do than that," he said.
But he insisted Mr Blair had not discussed standing down as an MP before the election.
Nor had they talked about the prime minister's life after his time in Downing Street.
Mr Burton added: "He has a great love of Africa and trying to improve Africa. I wonder whether he would get involved in that."
Commenting on the reports, a Downing Street spokesman said: "This issue is the last thing on the prime minister's mind.
"He is totally focused on the threat currently facing this country."
The Westminster rumour-mill has long been rife with speculation about what Mr Blair will do once he stands down from office, not least because he is comparatively young for a prime minister at 52.
He had been tipped for some big international role either in the EU or in the United Nations.
But Mr Blair is not reported to be seeking a frontline role outside British politics.
If he decides to leave Parliament, his successor will have to worry less about the accusations faced when Margaret Thatcher was hailed as a "back seat driver" in John Major leadership.
Clive Soley, former chairman of the Parliamentary Labour Party, said he welcomed greater openness about when the prime minister would leave Downing Street and Parliament.
It was a contrast from the gossiping about the departures of former prime ministers, he said.
Lord Soley said there were many roles Mr Blair could take outside politics - following the example set by former US President Jimmy Carter.
"I don't doubt that Tony's knowledge and grasp of world affairs and his reputation around the world could be used in all sorts of ways," he said.
The Labour peer said Mr Blair might pursue his interests in international or faith issues.
Lord Soley said he would like to somebody of Mr Blair's stature pushing through essential reforms at the United Nations.