Cherie and Gordon

London, Sept. 26: Cherie Blair spectacularly derailed Gordon Brown’s attempt to bury his differences with Tony Blair yesterday as he sought to present himself as the Prime Minister-in-waiting at the Labour Party conference.

As the British chancellor told delegates in Manchester that it had been “a privilege to work with the most successful ever Labour leader and Labour Prime Minister”, a journalist heard Cherie say: “Well, that’s a lie.”

Her outburst overshadowed one of the most important speeches of Brown’s career and exposed the simmering tensions at the top of the party despite efforts to present a united front in public.

Some six hours after the report surfaced, Cherie issued a denial. She told reporters: “Honestly, guys, I hate to spoil your story, but I didn’t say it and I don’t believe it either.”

But her friends let it be known that she was furious at what she believed had been constant attempts by Brown and his supporters to force her husband to stand down.

The controversy was deeply embarrassing for Blair, who, unaware of his wife’s apparent candour, had accepted Brown’s peace offering, smiling and shaking hands with the chancellor as the British Prime Minister received a three-minute standing ovation.

But it was potentially devastating for Brown, as it again called into question his fitness to be Prime Minister on the day that he said he would “relish the opportunity to take on David Cameron and the Conservative Party”.

Cherie was touring some of the conference exhibition stands as screens showed Brown extolling the strength and achievements of his relationship with Blair.

Carolin Lotter, a producer at Bloomberg Television, said: “She was walking towards me, coming from the auditorium area, and I had to step out of the way to let her pass when I heard her say the now very infamous words, ‘Well, that’s a lie’. The Prime Minister’s wife was not more than a metre or two away .I had to step out of the way; otherwise she would have run me down.”

Brown’s character has been an issue since former home secretary Charles Clarke described him as “a control freak” who lacked confidence and could not manage people in a “collegiate” way.

Blairite cabinet ministers at the conference have been adding to the questions about Brown’s character, saying they have been appalled by details that have emerged about the recent “plot” by his supporters to force Blair to set a date for his departure.

Brown’s credibility was further undermined last night by research commissioned by BBC 2’s Newsnight from a leading US pollster, Frank Luntz, which showed that a group of voters did not believe his assurances that he was not involved in the attempted “coup”.

Home secretary John Reid emerged from the poll as the favourite to succeed Blair.

Brown had desperately wanted to dispel doubts about his fitness to become leader by admitting past differences with Blair.

Coming as close as he could to an apology, he spoke of his “regret” that tensions between him and the Prime Minister had distracted the party and the government.

He made his most direct pitch yet for the leadership, delivering what a Labour MP described as “the longest job application in history”.