Tony Blair's chief-of-staff has denied saying Gordon Brown would never become prime minister.
There has been fresh speculation about Brown's chances
The Spectator magazine claims Jonathan Powell described the chancellor's hopes of entering Downing Street as a
The remarks were reportedly made as Mr Powell chatted to Spectator editor Boris Johnson while the pair stopped at traffic lights on their bikes.
No 10 says there was some "banter" but Mr Powell never made the remark.
And Mr Blair told BBC Breakfast: "I think the idea of my chief of staff giving interviews to Conservative MPs at the traffic lights on his bicycle is somewhat far fetched."
The Spectator says Conservative MP Mr Johnson raised the subject of relations between No 10 and the Treasury when he met Mr Powell at lights on London's Pall Mall.
Mr Powell reportedly replied: "It's a Shakespearean tragedy.
"Gordon Brown is like the guy who thinks he's going to be king but never gets it.
"He's never going to be prime minister."
But Tony Blair's official spokesman said: "Jonathan did not say it."
"There was some light-hearted banter on Pall Mall but the last person Jonathan would confide his inner-most thoughts to is Boris."
Mr Johnson later insisted the article was "100%"
"I'm afraid his memory must be playing him false," he said.
"I'm absolutely certain - I went away and wrote it down afterwards. I have
absolutely no doubt whatsoever."
Foreign Secretary Jack Straw refused to comment when asked about the report at a Labour
Party election news conference.
Asked about the chances of Mr Blair serving a full third term in office if Labour wins the next general election, Mr Straw said: "I only give odds on horse races."
'Up for it'
On Sunday he dismissed talk of his stepping aside in favour of Mr Brown as "decisions for the future".
But he said: "In the end, the British people are the boss - they're the people who make the decision.
"The reason that I'm up for it [leading Labour into the next election] is there's a lot more still to do."
Speaking on BBC's Breakfast with Frost, he had fulsome praise for his chancellor but stopped short of back him as the future premier.
Asked whether he would endorse Mr Brown as his successor, Mr Blair said: "These are decisions for the future, but I have always made clear the high regard I have had for him.
"It's been a great partnership - he's a brilliant chancellor. He's delivered huge economic strengths to this country.
"He's a tremendous asset to the party and the country."
The latest reports about Mr Blair's future were fuelled when Deputy Prime Minister John Prescott suggested Mr Blair could "follow the example of Harold Wilson", who stood down mid-term.
He said Mr Blair would have Labour's full support if he led the party into the next general election, but hinted that the prime minister could be derailed by "events".
Earlier, Mr Prescott suggested cabinet ministers were jockeying for position in case Mr Blair stood down.