Is Sarah Brown the most astute politician left in new Labour? Not only did she achieve in three minutes what her husband struggled to do in 53, to flick the nation's emotional buttons from am-I-bovvered to warm and smoochy, but her performance appeared utterly guileless.

She just tapped out a few little sentences that very morning, we are told. Maybe so, but this was - as Gordon might say - no job for a novice. Her words were pitch-perfect, the product of her laser PR brain.

How astute to remind conference of when she stood before them as a new bride (aw, bless), to “thank you all” for the “privileges of my life” (gratitude, humility - not whingeing about her sacrifices, like Cherie), of the “great moments, often private” (nor relishing the public limelight like Old Pixieboots either), “proud” to watch her husband's devoted toil (without shoving her oar in).

Even Fleet Street's reigning queens of mean praised the charming, poised, modest, self-deprecating Mrs Brown. And Sarah is all of those things. But her true defining characteristic is being so smart she never shows quite how smart she really is. And what her speech revealed was her grand mastery of the rules of Wife Power.

Long ago, women fancied they might storm the political citadel by the front door - now it looks a better plan to organise a charity tea party in the rose garden. It's a tired old fact that less than a fifth of MPs are women, putting Britain not only below most leading European nations, but those torchbearers of emancipation, Lithuania and Bulgaria. But then perhaps one in five female faces is plenty: the 14-hour days only send them flying off to their families eventually. And besides, women politicians are so damn annoying with their strident voices and bossy demands, the clothes and hairdos they never quite get right - too frumpy, too flirty, too flashy, too dowdy, just too wrong, wrong, wrong.

Wife Power, however, isn't grabby or shrill. It is fragrant, soft-spoken and well-tailored. It doesn't collide with mainstream power but upholds it, since a first lady's first priority is to bolster her husband's career by emptying herself of other interests or career pursuits. “Your love keeps lifting me higher”, in the words of Jackie Wilson's song, played as Sarah and Gordon's lips met.

And Wife Power runs in pretty parallel to the system. It doesn't sweat over the committee stage of grinding legislation: it slips on the sequins for a charity ball. It doesn't demand: it schmoozes, flatters, networks, requests. At G8 summits, while world leaders ponder global terrorism, their wives meet for the White Ribbon Alliance, a charity much supported by Sarah Brown, to improve maternal health in the developing world. It is enormously admirable. Who could not be incensed by a childbirth mortality rate of one in eight in many parts of Africa? But then why are the annual deaths of 500,000 women not discussed over the summit table, but in a first ladies' luncheon next door? Wife Power achieves a great deal through these discreet and unofficial channels, raises vast sums and inspires magnificent individual deeds.

Cindy McCain, who has long lived an entirely independent life from her husband in Arizona while he shinned the political pole in Washington, adopted a sick baby with a cleft palate from Bangladesh without even telling him first.

But do charitable gatherings that are as segregated as Saudi weddings promote female empowerment or thrust women back into the margins? Certainly when membership is defined purely by gender it attracts curious bedfellows, as when Sarah Palin appeared at a White Ribbon gala in New York this week. Great to see her new concern for reproductive health since hitherto her main contribution was, as Mayor of Wasilla, to start charging sexual-assault victims for their rape investigation kits.

But Wife Power isn't just about good deeds: it is about glamour and serious dressing up. That a man can be measured by the comeliness of his spouse, that his standing can be assessed in the quality of her grooming is a new and imported notion. In 1999 the wives of the American Ryder Cup golfers suddenly turned up in identical outfits. The European wives, in their smart but disparate get-ups, were accused of damaging their own husbands' morale and - instead of guffawing at the go-go boots and stars-and-stripes hotpants of their rivals - resolved to get their own doors-to-manual team kit next time.

Likewise it is now hard to imagine a British party leader with a wife like Ken Clarke's private and studiedly unglamorous Gillian or David Davis's defiantly mumsy, constituency hermit Doreen. Nothing less than effortless chic is required, the ability to look classy in democratically priced high street duds. But since peacocking is not Sarah Brown's strength, how clever of her to play to her strong suit.

Until she took to the podium, it was widely agreed that a PM's wife should remain silent. This created mystique, avoided potential clashes of opinion with her husband, implied a lack of meddling in government business, gave the press less to chew over and, frankly, look what happened when Cherie started opening her trap. And in the looking-lovely-while-saying-nothing stakes, Sam Cameron has become undisputed champion, posing patiently on chill Cornish beaches in fetching swimwear and sarongs, puckering up to Dave according to the spin specifications of Andy “Alastair” Coulson.

How alarming for Sam to realise that perhaps picking out a pretty lemon coat from Topshop and product-placing a Smythson handbag might not be enough this year. Silence is easy compared with saying the right thing, as the wives of the presidential hopefuls will attest. Drowning in the deep waters of policy is the chief danger, but even making affectionate jokes at his expense, like Michelle Obama's quips about her husband's morning breath, dubs you ball-breaky. While every time Cindy McCain speaks, she looks likely to shatter into a thousand fragments, so scared is she of uttering the wrong thing.

Visiting a state school this week, I was told they'd started teaching the new “sport” of cheerleading. No wonder the glass ceiling remains uncracked when girls, for all their superior grades and mental application, are funnelled eventually into the role of male helpmeets and the balmy backwaters of Wife Power.

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