In the first extract from her autobiography serialised in The Times, Mrs Blair disclosed that her husband would have stood down as Prime Minister before the 2005 general election if Mr Brown had been prepared to back his public service reforms.

Mrs Blair said her husband had suffered a "crisis of confidence" over the Iraq war, fearing that he had become an electoral liability. But she said he decided that he had to stay on to entrench his plans for city academies, foundation hospitals and pension reform.

She said Mr Brown was "rattling the keys above his head" and failed to understand that Mr Blair would have quit if he had supported his reforms.

"Tony would have stood down, there is no question", she said. "Instead of which, Tony felt he had no option but to stay on and fight for the things he believed in.

"I was convinced that if Tony failed to stand for a third term, it would be seen as a response to the negative criticism of the war. It would be read by history as a tacit admission of failure."

In an interview with the paper, she said Mr Blair was now advising Mr Brown through the current political turmoil and counselling him on how he could win the next general election.

"I know that Tony thinks Gordon could win the election and I know that he has spoken to Gordon about how he could do that. Tony has given Gordon advice. He and Gordon talk to each other even now."

She told the newspaper she took no pleasure in Mr Brown's current troubles and would "be delighted" to campaign for the Labour Party in future.

Mrs Blair's book, Speaking For Myself, is also being serialised in The Sun. In an interview, she played down the animosity between her and Mr Brown, saying: "If I've had any problems with Gordon, it was only because I thought he was putting too much pressure on Tony to leave when Tony wasn't ready."