MANCHESTER, England — Prime Minister Blair’s wife, Cherie, suggested during a speech by Chancellor of the Exchequer Gordon Brown that his account of his relationship with her husband was “a lie.”

Cherie Blair left the conference hall with her security detail as Mr. Brown was speaking to the Labour Party conference in Manchester, England, yesterday. As she walked through a display area outside the auditorium, Mr. Brown was on television monitors, extolling the strength and achievements of his political relationship with Mr. Blair. “Well, that’s a lie,” she said, apparently unaware that she was within earshot of a Bloomberg News journalist.

A spokesman for Mr. Blair said the account of his wife’s comment “is completely untrue. Mrs. Blair was going round the stalls at the conference center when the chancellor began speaking, and she went immediately to the stall organizer’s office to watch the remainder of the speech on TV. She certainly didn’t say that.”

Cherie Blair later also spoke to reporters in Manchester to deny the statement. “Honestly guys, I hate to spoil your story, but I didn’t say it, and I don’t believe it, either,” she said.

Mr. Brown’s speech came at a time of deep divisions within the ruling Labour Party between those who want him to succeed Mr. Blair and those who accuse him of plotting to undermine the prime minister’s leadership.

The remark by Cherie Blair, a 52-year-old human-rights lawyer, may undermine efforts by both the prime minister and chancellor to smooth over their differences before Mr. Blair, 53, surrenders the party leadership and the premiership, which he says he’ll do within the next year.

The prime minister would have been hoping that this, his final party conference as leader, would have allowed him a triumphant exit as the most successful Labour prime minister ever, a professor of politics at Nottingham University, Philip Cowley, said.

“This is something they’ve all been trying to avoid,” Mr. Cowley said in a telephone interview. “They would have hoped for a Frank Sinatra-style exit, singing ‘My Way.’ One careless remark seems to threaten to blow that apart.”

Mrs. Blair’s remark was not a surprise, a lecturer in government at Essex University, Thomas Quinn, said.

“It fits into what we already know,” Mr. Quinn said in an interview. “Newspapers have said that she has told Blair she didn’t want Brown to take over.”

The debate over when and how Mr. Blair should hand over power has obscured discussion of policy issues within Labour since the last election in May 2005. Mr. Blair has been in charge of the Labour Party for 12 years and won three general elections since Mr. Brown stood aside in 1994 to give him a clear run at the leadership.

Since September 2004, when Mr. Blair announced he didn’t want to fight a fourth election, there had been speculation among Labour lawmakers and in the British press about the exact date of his retirement. Until earlier this month, Mr. Blair had refused to set any timetable for his departure.

That refusal, reaffirmed in an interview on September 1 with the Times newspaper of London following his summer vacation, led supporters of Mr. Brown, 55, to press for Mr. Blair’s immediate resignation. On September 6, eight junior members of the government quit their posts, saying Mr. Blair was a liability to the government.

The next day, the prime minister made an appearance outside a school in north London to announce he would quit within the next year. Mr. Brown was pictured in the Financial Times and Daily Telegraph newspapers smiling following meetings he had with Mr. Blair, prompting accusations that Mr. Brown had a hand in the plot to win the promise from the prime minister.

Since then, Messrs. Blair and Brown have attempted to paper over their rift, expressing support for each other and pledging an orderly transition of power. Mr. Blair has said he’ll name an exact date at a later time. Mr. Brown said he backs that plan.

Mr. Brown, facing a slump in Labour’s opinion-poll ratings, told activists yesterday that he is the best man to defeat a resurgent Conservative Party.

Mr. Brown’s speech was intended to defuse questions raised by former Cabinet ministers including Charles Clarke, who said this month that the chancellor is a “control freak” who forced Mr. Blair to make a public promise to step down within a year. Cabinet ministers including John Reid and Alan Johnson have suggested they may challenge Mr. Brown for the leadership.

An opinion poll by YouGov Plc showed 27% of voters said Mr. Brown will make a good prime minister, down from 36% in March. Labour trails the Conservatives by 31% to 38%. The survey of 1,734 adults was conducted between September 19 and 22. No margin of error was given.

Yesterday, Mr. Brown praised Mr. Blair and said he would stick with changes to the party put in place since Mr. Blair became leader in 1994. He said he and Mr. Blair put disagreements behind them, aiming to focus the party on winning another election.