Cherie Blair is writing a “full account” of her journey from a working-class childhood to life in Downing Street – and the more explosive it is, the more money she will get.

If Mrs Blair has promised a warts-and-all account of her dealings with Gordon Brown, Carole Caplin and Alastair Campbell, her advance could exceed the £1 million reportedly paid to Mr Campbell for his diaries The Blair Years.

However, publishing insiders said that the advance could be as little as £250,000 – less than that offered to David Blunkett and John Prescott – if she intends to skim over the conflicts at the heart of new Labour in order to protect her husband’s reputation. The book will be published in October next year, with Mrs Blair expected to deliver a first draft in the spring.

There was no bidding war for Mrs Blair’s autobiography; instead, her literary agent, Kate Jones at ICM Books, took an outline straight to Ursula Mackenzie, the chief executive and publisher of Little, Brown. It was Ms Mackenzie who handled the most revelatory political memoir of modern times – Edwina Currie’s stunning confession of her affair with John Major, which was exclusively serialised in The Times in 2002.

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Westminster gossips immediately homed in on whether Mrs Blair, who is not known for being taciturn, might dent the fragile revival of the friendship between her husband and Mr Brown. The pair talk frequently and the Prime Minister now refers to his predecessor as “Tony” in private conversation.

Mrs Blair was widely held to harbour deep resentment at the way the former Chancellor manoeuvred against her husband. When, in his speech to the Labour conference last year, Mr Brown declared that it had been a privilege to have worked with her husband, she was overheard saying: “Well, that’s a lie.”

Interest also centred on what Mrs Blair might have to say about her infamous reliance on Carole Caplin and how she came to be embroiled with the conman Peter Foster in the purchase of two flats in Bristol, leading to her tearful public apology in which she admitted: “I’m not Superwoman.”

Mrs Blair is said to have been on frosty terms with members of the Royal Family, including the Princess Royal. But of greatest interest to many could be the light her account may shed on her husband’s decision to go to war in Iraq, the personal circumstances that led him to contemplate quitting in 2004, and the tortuous handover to Mr Brown.

Mrs Mackenzie said that she was not expecting Mrs Blair to pull any punches “It will be her putting the record straight from her point of view. She is characteristically frank and I know that she’s keen to put everything she can into the book.

“I’m not in a position to say what she’s going to put in because she’s in the middle of writing it, but it will be a straightforward, funny account of a rather extraordinary life.”

Mrs Blair said: “I feel so privileged to have travelled so far. So much has happened – things that my grandma could never have dreamt of – that it feels wrong somehow just to let it pass as if the journey had no meaning.”

Labour officials, busy planning for Mr Brown’s first party conference as Prime Minister next week, were caught off guard and feared the damage her book might do to the party. A source said: “Many people in Labour lost patience with Cherie a long time ago, and whereas Alastair Campbell had credit in the bank which allowed him to spill the beans, Cherie has none. If she makes life difficult that will be the end of her reputation for many in the party.”

Little, Brown refused to release details of Mrs Blair’s advance beyond confirming that no newspaper serial-isation deal had been struck.

Katherine Rushton, of The Bookseller magazine, said: “Cherie Blair could have earned an advance of up to £1 million, depending on how frank she is prepared to be about the Downing Street decade, the Brown-Blair relationship, and the scandals around Carole Caplin and Peter Foster. The advance will have been inflated because she is publishing relatively quickly and the possibility that Mr Brown will call an election in the publication year.

“It’s very hard to put an estimate on the number of copies the book could be expected to sell – 50,000 in hardback would be a good result and one I think she could achieve. If Cherie gets the book right and it does very well, she could be looking at 100,000 in hardback.

“She is like Marmite in that she totally divides opinion, but with the amount of controversy that surrounds her I think she could scoop up as many sales from her detractors as from her fans.”

Several political autobiographies have sold disappointingly, but John Major’s is believed to have sold 200,000 copies. The first volume of Baroness Thatcher's autobiography, The Downing Street Years, is thought to have sold more than half a million copies.

Iain Dale, the founder of Politico’s bookshop, said: “The advantage she has is that because she is not well thought of by many people she’s got nothing to lose.”

Insiders

The Blair Years Alastair Campbell (71,850 copies sold to date)

Under pressure after the Hutton inquiry into the death of David Kelly, Campbell contemplated suicide himself

The Spin Doctor’s Diary Lance Price (6,530)

Reveals that Blair shouted “f***ing Welsh” when it looked as if Labour might lose the first Welsh assembly elections

The Blunkett Tapes David Blunkett (4,142)

Writes that he once mistook Prince of Wales’s aftershave for the smell of his lavender bushes at Highgrove

Source for book sales: Neilsen BookScan

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