What could possess an intelligent, urbane woman of maturing years to make her stand on a hardback chair, bend over like a table dancer at Spearmint Rhino, then post the resulting image on Facebook?

No, me neither. It is beyond all understanding. Yet this is what Lady Shelley Sawers, wife of the new head of MI6, elected to do, thus making her husband look a bit of a tit.

Posting details of her family’s holidays and pets, with a photograph of Sir John Sawers wearing nothing but a pair of snug-fitting Speedos, has, say critics, compromised his security. I think this is nonsense. If our enemies rely on the likes of Facebook and Twitter for their intelligence, then we have nothing to fear. All they will discover is that people use a lot of exclamation marks in their correspondence and that Phillip Schofield had a bad day at the weekend because he put unleaded fuel in his car instead of diesel (aaaaarghh!!!!).

But Lady Sawers’s Facebook page has highlighted a different conundrum — why so many people feel the need to advertise such domestic banality at all. If we discount the small matter of her husband’s job, Lady Sawers was only doing what millions of bored, middle-aged wives do the world over — serving up, unbidden, entire photograph albums of themselves and their families on social networking sites, like all-singing versions of the dreaded “round robin” Christmas letter.

The reasoning is that they are keeping friends and distant relatives “up to date” with family news. But, just as with the round robin, this is frequently a ruse. The photos, woven together like the best bits in Big Brother, are carefully selected to communicate other messages, such as: Look what fun we have as a family/ Haven’t we done well/ We’re so cool, our teenage children still want to hang out with us . . . and, crucially, AREN’T I LOOKING HOT FOR MY AGE??

In her “Sally Bowles” chair photo, Lady Sawers, a teacher, is pictured alongside her daughter, 22, who is striking an identical pose. At a stroke we see not only that mother and daughter have a “GSOH” but also that Lady Sawers has managed to keep a spectacularly good figure. Hats off to her for that. But the subtext of the picture, unintentional though it may be, is “Not bad, eh?”

Lady Sawers’s photos, though, are utterly tame compared with some of the images that middle-aged women post online. Take a stroll through the world wide web and you’ll see galleries of females of a certain age pouting and flirting with the camera like Dick Emery drag characters. Some pose coquettishly alongside their lookalike teenage daughters — translation: “We could be sisters” — and the more extreme cases appear in magazine articles where you have to guess which is the child and which the parent (clue: the child is the one without the nose veins). I was once shown a beach snap in which both daughter and mother were topless and holding matching cocktails. One was 21 and the other 53.

The female midlife crisis used to be a hidden, silent beast but now it has come roaring out of the closet with an ankle tattoo, a tummy tuck and a wardrobe full of Topshop clothing. The internet is its accomplice, allowing women to live out their second youth and attention-seek to their hearts’ content. The midlife crisis syndrome also causes blurring of maternal boundaries, leading some fiftysomethings to toss back their hair extensions and sigh “we’re actually more like best friends than mother and daughter”.

Last year Jade Jagger was photographed partying away at a fashionable London shindig with her daughters Assisi, 15, and Amba, 12. All three wore minidresses and designer heels. The Duchess of York, aka “chummy mummy-in-chief”, has proudly boasted of “going on the pull” with Beatrice and Eugenie, causing the nation to make a collective dash for the sick bucket. The days when children could cling to the comforting illusion that their parents never, ever had sex, and had only ever done so for the purpose of procreation, have long gone.

Have you noticed that in this, the age of Madonna’s 50-year-old crotch shots, there has emerged a certain type of predatory hag who seems to think it OK to grab young waiters’ bottoms in restaurants and growl “Phwoar, if I was ten years younger . . .” while her whooping female friends egg her on. A middle-aged journalist wrote recently of her revulsion that a divorced friend had started to flirt with her 17-year-old son, leching over his body and asking if he was “spoken for”. If the situation were reversed, she reflected, and fortysomething male friends propositioned her teenage daughter, it would be classed as sexual assault.

The female midlife crisis is now aping the traditional male one, right down to the tight leather jeans and the super-size dose of self-delusion. In some ways this is good. Years ago women mourned the loss of their youth quietly and sadly, swapping their miniskirts for Crimplene slacks and ceasing to see themselves as sexual beings. My friend remembers her mother wearing the same nylon pinny every day for four years. She was barely 40.

But none of this means that it isn’t a bit grotesque when a woman of 48, with bingo wings, wears a Little Miss Naughty T-shirt. It doesn’t make it OK for her to mortify her teenage son by giggling kittenishly with his friends and comparing body piercings.

Dressing up mutton as lamb can only lead to hurt feelings — as anyone who has been wolf-whistled from the back while wearing shorts, only to hear the whistles fade as the builders clock the front end, can testify. In my defence, it was a hot day.

We laugh at ageing men who buy a Ferrari and tease their comb-over into a straggling ponytail look. Don’t let’s totter down the same path in our “f**k me” shoes. Otherwise we may as well jump aboard that Trafalgar Square plinth and stand there wearing a too tight T-shirt bearing the slogan “Little Mrs Desperate”.

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