I first met Sarah Brown in Margaret Thatcher's bedroom. Our children were playing in a sea of toys beneath long floral curtains chosen by Norma Major - a play date organised by that unlikely nanny Damian McBride. When we decided we wanted some tea, a multilayered silver tray appeared full of fancy little cakes, courtesy of some sort of diplomatic gathering downstairs. I glanced at the wife of the then chancellor over the trolley (trying to shake an image of Mrs Thatcher in the en suite bathroom), looked at the children disappearing among the toys in this ad hoc nursery and thought: your life is surreal.
That surrealism pervades Mrs Brown's memoir of life at No 10 Downing Street. Gordon rescues HBOS; Sarah is off to a charity auction. James Purnell resigns and Gordon's leadership totters - and the family is kept awake all night by rehearsals for Trooping the Colour. Mrs Brown discusses the death of the Big Brother star Jade Goody with a concerned Jesse Jackson Jr, and growing vegetables with Michelle Obama. A family summer holiday lasts six hours before a foot-and-mouth outbreak calls the PM back to London. A DBE intended for Graça Machel, the wife of Nelson Mandela, gets mixed up with a big shiny card made for her by the young John Brown. On a visit to Glastonbury to promote the international White Ribbon Alliance for Safe Motherhood, Mrs Brown has to take police protection, noting wryly: "I can't believe this will make me the most popular person at a music festival."
This is a domestic take on politics; the collision of the political with the personal. At one point, Sarah is woken at 5am and told by her husband to prepare to leave No 10 that day if the banking rescue package has the wrong impact. And when they do hurriedly leave, on 11 May 2010, the kids have to be reassured that their favourite duvets will soon follow them. There is a sweet story about Fraser telling his dad that when he grows up he wants to be a builder, a teacher and a dad. "Then he looked at Gordon and said, 'But you are just a dad.'"
The Prime Minister appears in the book as an occasional character, always kind and loving, always caring for his family, always dutiful to them and the nation - yet his appearance in the flat or at a family holiday, or chasing Sarah in circles around No 10 to try to catch a moment with her, only serves to underline the awkwardness of the lifestyle. In the midst of an idyllic summertime in Scotland last year, visiting friends and family and having children's sleepovers, "Gordon set down his perspective on the global financial crisis". The disconnect jars and is sometimes funny.
Much of the diary is told in a naive style - the wide-eyed child not quite believing that she is there. There's a touch of the John Major about Sarah Brown's style, with "I immediately joke", "needless to say" and "terrific" mugs of tea. If it's a little banal, there is a personal honesty, too - she talks, for instance, of being afraid to "make a giant fool of myself" when she has to speak at the British Fashion Awards.
This fear of public speaking - together with a sharp awareness of the number of highly glamorous women she has to appear next to - pervades the diary. Michelle Obama greets her with "At last, a normal-size person". Brown worries about her weight (a little), about her dresses (a lot), and about falling down in high heels (from time to time). "I am off again," she writes on 28 January 2010, "to fulfil my destiny of being photographed with every supermodel on the planet." She gets hair and make-up to "do their best for me" before being snapped next to Elle Macpherson.
The lack of budget for her wardrobe is a perennial complaint, not because Brown wants a cupboardful of designer dresses, but because she has to have endless outfits to wear in public - "there is a great call for a different outfit for every occasion" - and the failure to provide any financing for this (she is not allowed to receive gifts of clothes, either) underlines the vagueness of the position of what she calls WPM, Wife of the Prime Minister: "I have no exact status, no official position, masses of conflicting expectations both internally and externally, and a terrible suspicion that at any moment a great mistake will be made by ME!"
She has two staff, which "expands to a grand total of five" when she arranges the spouses programme for the G20 summit (the Obamas bring 500). On occasions, she is so exhausted that she faints and once has to be revived with Prince William's emergency oxygen - carried with him wherever he goes.
This lack of financial support for the WPM's office also adds piquancy to the indignant account of the small errors revealed in her husband's parliamentary expenses. As she notes, the family is significantly out of pocket from their position - "there are many costs associated with this job that are never reimbursed". One suspects that a reason for writing this book is to recoup some of those: the family is not wealthy.
Occasionally, Sarah Brown the former PR professional peeks through the curtain of famous names. There is a sharp awareness of the media: she notes a positive column about her husband's handling of the financial crisis by Paul Krugman in the New York Times; shows an inside knowledge of the political make-up of the Guardian's senior editors; and knows which video clips receive most hits on the Downing Street website (Maggie Darling's cat). Mostly, the media are present as a pest: relentless, hostile, intrusive, untrustworthy and dehumanised. The attention affects her friends, family and even her sister-in-law's children, who are bullied because their parents shared a cleaner with the Browns.
Sarah Brown signs up for Twitter (she now has over a million followers) in part so that she can show people a little of her daily life without having it twisted by the media - and because the WPM has no personal budget for communications. Like that decision, and like her tweets (and like that first play date in Mrs Thatcher's bedroom), this memoir, for all its personal glimpses, is ultimately a work of public relations.
First, it isn't a real diary: it was compiled last summer from notes, emails, letters and her schedule. Second, it is so full of "thank yous" - from the chap who agreed to let her have a venue at the last minute for some occasion to the 12 pages of acknowledgements at the end, from the son of the director of PiggyBankKids to Michelle Obama and the No 10 gardeners - that you sometimes feel you have wandered into a bridegroom's speech. But then, this is precisely the sort of thing that is genuine Sarah Brown - the thoughtfulness and the courtesy that prompted Piers Morgan, of all people, to surprise her publicly with a "good egg" award. Third and most important, political events and what must have been some fairly traumatic personal moments are so airbrushed as to leave the diary feeling a little empty, despite all the busy celebrity engagements and official trips overseas.
Shortly after entering No 10, Brown writes: "I believe that part of my role as WPM is to make an often extraordinary life as ordinary as possible for myself, my husband and my children. I intend to be good at that." And now she has done it for the rest of us, too.
Behind the Black Door
Ebury Press, 464pp, £18.99