Leaving Downing Street for the last time, Cherie Blair felt it necessary to bid a personal farewell to the press. She might have blown them a kiss drenched in irony, but she opted for a sarcastic remark. "I don't think we'll miss you," she called to reporters, her hostility plain to see.

If it's any kind of perverse consolation, the feeling is not mutual. The press will miss Cherie desperately. She fascinated them long before her husband entered Downing Street. Brilliant, accomplished, a career woman and mother, she was the myth of Superwoman made flesh. As such, she was what some sections of the media crave: a woman who needed to be taken down a peg or two. What will the fashion police and etiquette authorities do now there's no Cherie to kick around? Why, they'll focus on the new lady of the house, Sarah Brown.

Mrs Brown knows from her time in public relations what kind of scrutiny she is now under. So far, she has been the epitome of restraint, refusing interview requests, content to stay in the background, smiling but not fawning. So far, this has met with approval bordering on adoration, a lot of it from women, often Cherie's harshest critics.

One writer, commenting on Mrs Brown's choice of outfit for Gordon's elevation, said: "In a week of relentless personal appearances, Sarah has confirmed herself to be ready for the role of First Lady. She is an asset to her husband and will no doubt earn an army of fans across the UK in no time." Another member of the sisterhood observed: "She has a quiet self-possession that will serve her well in her new role."

Betting types might like to speculate when, rather than if, this sympathetic coverage will change. In the months to come those who are now her media chums will start to wonder if that dignified silence and self-possession aren't a bit too Stepford Wife.

The closet of her past will be checked again for skeletons. Like her friend, J K Rowling, Mrs Brown is doubtless determined to play the media game by her rules and win. Cherie thought the same.

Oddly enough, Cherie should be the very woman Mrs Brown looks to in her hour of media need. As PR strategies go, this one is very simple and doesn't need a team of advisers to implement. All Sarah Brown need do is take a piece of A4, write down everything Cherie did, and do the opposite. Be the anti-Cherie, in short.

Apart from the obvious no-nos, such as buying property with the aid of a convicted conman and wearing white pixie boots, the rest comes down to abiding by one basic rule: to thine own self be true. At the core of Cherie's troubles lay an inferiority complex the size of Mars.

Despite everything she had achieved, Cherie craved acceptance. She went from a world in which brains mattered to one where looks and status were considered paramount, and she panicked. Her entire time in Downing Street can be seen as one long bout of hyperventilation - about her clothes, her weight, her bank balance, her social standing, her career.

This explains the arrival of "lifestyle guru" Carole Caplin, whose extraordinary cv included a stint as a topless model. Caplin was a Rasputin in slingbacks, providing Cherie with all the services of a best friend but charging for the privilege.

The old Cherie, with a first from the LSE and first place in the bar exams for her year, would have subjected this notion to merciless examination. The new, desperate, all-at-sea Cherie embraced it without a second thought.

A Carole Caplin type wouldn't get through the door of 10 Downing Street now. Even so, though very different women, Sarah Brown and Cherie Blair have more in common than first appears. An important point in both their lives was the ending of the parental marriage. Cherie was eight when her mother and father split, Sarah seven.

The key difference thereafter seems to have been wealth. Cherie Booth's upbringing was north of England and working class, Sarah Macauley's was middle class and metropolitan. This gave the latter a natural ease around money and privilege. She didn't have to fit in; at her school in Camden she defined "in". Later, with her PR firm Hobsbawm Macauley, she did the same for New Labour.

Sarah Brown now possesses the great gift of acting like a woman who doesn't need to prove herself. It's a quality, as Cherie found out, that no amount of money can buy or lifestyle gurus bestow. It's telling that Cherie, even though she can now disappear from the spotlight, seems reluctant to go. Her next appearance will be in a BBC documentary next Wednesday called The Real Cherie.

Whatever lies ahead for Mrs Brown, it's safe to assume that in a decade from now there won't be a programme called The Real Sarah in the schedules. Best guess is we are already looking at her.