It was three years before Sarko saw Cécilia again. He was also married but that didn’t stop him being “struck by lightning”. The couple duly had an affair, before eventually leaving their respective spouses. They married in 1996.

Then, in 2005, Cécilia broke the cardinal French rule of being discreet concerning illicit affairs and had a very public liaison with PR executive Richard Attias, a dashing 49-year-old Moroccan.

The pair moved to New York and pictures of them were published on the front cover of Paris Match. The editor was fired, but the damage was done. Eventually Nicolas wooed Cécilia back, although he did manage to fit in a quick affair with a young political journalist beforehand.

Infidelity in France is nothing new; sharing it with the rest of the nation is. François Mitterrand, for example, was tight-lipped about his affairs.

“There is a rumour, Mr President, that you have a mistress and a love child,” a journalist once said to the President. “Et alors?” was Mitterrand’s response. “So what?”

His mistress, Anne Pingeot, could be credited with starting the trend for hanging out the presidential washing in public, although she at least waited until her lover was dead. Then she showed up at his funeral with their lovechild in tow.

The French don’t mind infidelity.

It is well known that President Jacques Chirac has been constantly unfaithful to his wife Bernadette. Félix Faure apparently died at the Elysée Palace while having oral sex with his mistress in 1899. There are worse ways to go.

For the French, a leader’s sex life has no bearing on whether or not he can or should run the country. Public trust and private lust are kept separate.

They were astounded by the fuss made of the Bill Clinton and Monica Lewinsky liaison. “For us, if the President has sex with an intern it’s not a bad thing,” one friend told me. “Because men are terrible if they don’t have sex.”

Women are just as entitled to their petites aventures, which is why the public has not turned against Cécilia, despite rumours of a divorce being imminent. “I would imagine most Frenchwomen would applaud her for getting out of what I presume has become a loveless marriage,” says another French friend. “Or has she been bonking someone else? In which case they’d applaud even louder!”

The French rather like Cécilia. A mother of three, she is everything a chic French woman should be: tall, slim, elegant. Most people don’t care what goes on between her and her husband. “We’ve had enough of this!” said one commentator on the Nouvel Observateur website commenting on a possible divorce. “With all the problems going on in France, this is really insignificant.”

Another reader pointed out that they didn’t vote for Cécilia, they voted for her husband – something Cécilia apparently failed to do herself during the election.

Since Sarko took office in May, she has been conspicuous by her absence from his side. “I don’t see myself as a first lady,” she has been quoted as saying.

“That bores me. I am not politically correct.” She refused to have tea with President Bush when the couple visited America. She skipped a visit to Bulgaria last week, where she was due to receive the country’s highest award for her part in freeing six Bulgarian medics from a Libyan jail. Nor did she show up at the Rugby World Cup semi-final on Saturday.

Maybe she had a premonition of the final score – or another rendezvous?

The latter is more likely. Let’s face it, if Frenchmen are sleeping around, then so are Frenchwomen. They see their petites aventures as one of the good things in life that one shouldn’t deny oneself, rather like a mature piece of Brie or a square of exquisite dark chocolate.

French female infidelity has a long and illustrious past.

Eleanor of Aquitaine, for example, cuckolded her husband Louis II way back during the second crusades. Nobody in France disapproves of literary heroine Emma Bovary for cavorting with the young Léon in the back of a horse-drawn carriage.

“Our culture of l’amour libertine is a heritage we cannot avoid,” says a friend of mine. “We have grown up with Les Liaisons Dangereuses and with characters such as the Marquis de Sade and Colette.”

It is said that if you cut a Frenchwoman in half, you will see the words liberté, égalité, fraternité written throughout, like a stick of rock. Of these the most important is liberté. Women are free to marry, and then to misbehave.

“Everyone does their own thing in their own corner,” the French designer Chantal Thomass told me. But what Frenchwomen do insist on is discretion.

If they criticise Cécilia it is not for being unfaithful but for getting caught out. Never before has a first lady publicly humiliated a president.

So are we seeing a new generation of Frenchwomen who will not put up with infidelity, or who will stray before their husbands get the chance?

The stoical behaviour of women such as Bernadette Chirac is seen as old-fashioned and weak. “Women are not willing to put up with being treated badly any more,” says a businesswoman acquaintance in her mid-thirties.

“And now that they have their own careers and incomes, I think we will see a lot more women acting like Cécilia.”

Rumour has it that she has left the Elysée Palace and moved to a suite at the five-star Beau Rivage Hotel in Geneva.

The occasional presence of Richard Attias in the city has been hinted at as a factor but he is known to be dating the French actress Mathilda May.

It is claimed that the first lady is to give an interview next week putting her side of the story, and if, as one Swiss newspaper is claiming, Cécilia has simply tired of Sarko’s multiple infidelities, then the rules of love and fidelity in France have been dramatically redrawn.

And it is Sarkozy who looks like becoming the first victim of the new regime.

• Helena Frith Powell is the author of ‘Two Lipsticks and a Lover’, published by Arrow at £6.99