We all know what Cherie's real crime is, don't we, girls?

It's taken more than a silly lie and dodgy friends to put Mrs Blair in the media dock

Forget the weird friends, the acupuncture needle and the pendant with healing powers. Let's even forget, for a moment, the convicted conman, the purchase of two flats in Bristol and the ill-judged lie to her husband's official spokesman. There is a problem with Cherie Blair, but it is not the one that has provided so many pages of triumphant copy in the tabloid press.

Mrs Blair or Ms Booth – the two names are an apt symbol of the dilemma she continually finds herself in – has not done anything illegal. On the contrary, she has behaved in exactly the same manner – taking advantage of soaring house prices – as many of the people who read the Mail on Sunday, the paper that started last week's feeding frenzy. No doubt some of them have already made a great deal more loot than Mrs Blair will ever do, given that her foray into the world of property speculation has come rather late.

The Blairs' financial manoeuvres, at a moment when many Labour voters are horrified by the Prime Minister's enthusiasm for university top-up fees, are hardly well-timed. The fact that they can afford to buy a £265,000 flat for their student son shows how out-of-touch they are with the real world, where many students struggle to pay rent, and higher fees would deter bright kids from applying to university.

Not for the first time, the home life of the Blair family has been shown to be very different from that of the rest of us. On this occasion, Mrs Blair's judgement has also been called into question, yet in circumstances that are richly ironic. Had the Blairs hung on to their family home in Islington, which they unwisely sold after the 1997 general election, they would have seen a much more substantial profit than they are likely to receive from a couple of flats in the West Country.

What the Prime Minister's wife is guilty of, if indeed she is guilty of anything, is behaving like a middle-class Tory voter – and not doing it very well. Taken on its own, the transaction hardly provides rich pickings for hostile newspaper editors, but cashing in on the housing boom is not the only thing Mrs Blair is not very good at. It is generally agreed that she is clever, ambitious and an excellent mother, displaying a startling degree of fecundity at a moment when women 15 years younger are resorting to fertility treatment.

You do not have to be a wholehearted fan of Mrs Blair – and I am far from being that – to recognise that some of the attacks on her are motivated by envy. The Prime Minister's wife comes too close to having it all, but she also suffers from what may be the worst imaginable handicap for a woman in her position: she is emphatically not photogenic.

Her face is mobile, she is often pictured with her mouth wide open, and she rarely seems to be at ease with herself. There are women who do not care about these things but Mrs Blair is not one of them, judging by her reliance on friends such as Carole Caplin for fashion advice and fitness training. The Prime Minister's wife and the former glamour model are an odd pairing. Old pictures of Caplin show a woman happy to show off her body – precisely the opposite of what Mrs Blair seems to be.

She gives every impression of suffering from the traditional insecurity of clever women who suddenly find themselves thrust into the limelight. Misogyny has always been an unappealing feature of public life in this country, but these days the assaults are much more frequent and vitriolic. The Sun's loutish columnist, Richard Littlejohn, regularly abuses Mrs Blair as the "WW" or "wicked witch".

Mrs Blair is a Catholic but in this climate it is not so hard to understand her habit of resorting to a circle of style advisers and New Age gurus. The Princess of Wales did much the same, but her reliance on an even kookier set of people – astrologers, psychics and so on – was generously interpreted as another of her endearing eccentricities.

In Mrs Blair's case, no such quarter is given. She cannot slip into a pair of jeans and an old cardigan at the end of a long day without considering that her latest style "gaffe" might appear on the following day's front pages. This vulnerability is her Achilles' heel, and she has responded, unsurprisingly, by trying to erect an impenetrable fence around what she regards as her private life.

The Blairs do not always get it right, posing with their family for a Christmas card some years ago and then claiming that anything to do with their children is off limits. But on this occasion Mrs Blair's instinct to resist impertinent questions, when her purchase of the two Bristol flats was first queried by the Mail on Sunday, was right. If deals that are neither unethical nor illegal are to be subject to such hostile interpretation, there is a real danger that talented people will be deterred from entering public life.

Mrs Blair's mistake was to lose her nerve and tell a silly lie, not to the newspaper itself – I am increasingly of the opinion that all decent people have a moral obligation to mislead the Mail as often as possible – but to Downing Street spin doctors. In doing so, she provided a unique opportunity to her husband's enemies; for more than five years, Tony Blair has posed a problem for right-wing editors and commentators, who are at a loss to know how to inflict lasting damage on a prime minister whose prejudices so closely match their own.

This is a Labour leader who stands up to the trade unions, adores rich businessmen, sucks up to the most reactionary US president for decades and is apparently prepared to go to war against the wishes of many of the people who put his government in office. At the same time, what the right loathes about Blair – a liberal social agenda that includes legal recognition of same-sex partnerships and allowing unmarried couples to adopt – is far from unpopular with voters, as the Conservative Party has discovered to its cost.

Given that the Prime Minister also goes to church, admires the Queen and leads an impeccable private life, the opportunities to land a lethal blow are frustratingly rare. And that leaves Cherie, who is now being portrayed as frankly bonkers in a blatant attempt to undermine her husband. Open season has been declared on her, with other tabloids eagerly following the Mail's lead.

The allegations get more lurid and personal by the day, going far beyond the original claim that she unwisely accepted financial advice from a convicted fraudster. She has consulted a dietician! She paid £120 for a harmonising facial! She took part in a rebirthing ceremony in Mexico!

This brings us to last week's other great irony, which is that these claims come from the very same newspapers that are themselves obsessed with feng shui, astrology and wonder diets. On Friday, the Daily Mail magisterially rebuked the Prime Minister and his wife for "cynically misleading the media and civil servants in Downing Street".

The paper's fearless quest for truth continued on the very next page, with an article describing "the day the aliens landed" in Suffolk. This turned out not to be another reference to the Blairs, but an exposé of a UFO sighting which successive governments have covered up for 20 years. The Prime Minister's wife may have some unusual friends, but at least no one has accused her of believing in little green men.