This summer I was in a taxi from Cap d'Antibes to Nice, motoring for miles along the Cote d'Azur via both the Route du Bord de la Mer and the Promenade de la Plage. I sat on the left in the back, a 15-year-old boy of my acquaintance was on the right, behind the driver.
"If you stopped playing with your BlackBerry," I said, after a while, "and bothered to look out of your window, I think you'd find it interesting". Indeed, from this point on, the boy did find our route more diverting and indeed scenic than his tiny screen, as around half the women bathers on the beach only a few yards away from Tarmac had, like the Duchess Of Cambridge, opted to remove their bikini tops and were strutting around, smoking, reading, or standing in the sea chatting, topless as the day they were born.
Now there is one, crucial, difference between women who choose to go bare-breasted on public beaches in the South of France and Kate Middleton. The wife to the heir to the throne only disrobed on the terrace of a private house because she wrongly assumed the only witness would be her husband, not the whole of France (at the time of writing, the pictures have only been published in French Closer, and are not available online).
France may have fierce privacy laws, but every summer, its weekly gossip mags publish intrusive photographs of celebrities "romping". After all, Paris Match invented the sport, and there's been a voyeuristic market for such shots ever since Jackie Kennedy stripped nude to sunbathe and practise yoga on Skorpios, her husband Aristotle Onassis's private island, in front of the prying lens of a photographer disguised as a gardener, in 1971. This year, the "First Lady" Valerie Trierweiler was papped in a blue bikini, images that received a wide distribution, even in the magazine Trierweiler still works for, Paris Match. (She sued one, VSD, but only received 2,000 euros in damages).
And every year Voici publishes images of the TV presenter Claire Chazal seins nu in Corsica, it's a traditional sign of summer, like swallows. So the rule of thumb is, basically: if you're famous, and don't want to appear in Paris Match half-naked, don't take your top off.
But the other crucial difference is this. Everyone will think there's a "When in Rome" factor about Kate's toplessness. I don't. I'm surprised she did it. You don't really avoid "tan lines", as Closer has speculated of the Duchess's decision, if you then coat yourself thickly with Factor 50, and as the 15-year-old boy noted in Nice, many of the women who had taken their tops off were "old, Mum!"
The reason I'm surprised is because bap-flashing is not just bad for the skin, it's a sign of age. "Twenty-five years ago, it was de rigueur everywhere, not just the South of France," says the world's top beach correspondent, Catherine Fairweather, the travel editor of Harper's Bazaar. "It really took off (no pun intended) in the Seventies, as an extension of women's lib, but now, in all the chic resorts, all the young women have their tops ON."
This is all very confusing, I know. Depending on the decade, and the country, there are different attitudes to bare flesh. (I'll never forget being reported to the police by my neighbours in Washington DC in the Nineties for allowing my toddlers to frolic naked in my backyard.) Basically, swimming or sunbathing is so fraught with risk for celebrities that famous women like Nigella and Madonna, if they don't want to end up on websites, ogled by millions (and they don't) now go the other way from Onassis, and don long-sleeved sunsuits or "burkinis''.
So, in fact, the Duchess's toplessness - even though she was only exposing herself to her husband - far from being risque, was oddly old-fashioned, and… an incy-wincy, teeny-weeny bit St Tropez in the Seventies.