For the Anglo-Saxons, adultery is as French as red wine and baguette

Paris Letter : Like so much of French cultural life these days, the manner of Isabelle Adjani's break-up with the musician Jean-Michel Jarre was imported from Americam writes Lara Marlowe.

When the star learned that her lover of two years had started a liaison with the actress Anne Parillaud (best known for her role in Luc Besson's Nikita), Adjani told Jarre to get lost - on the cover of Paris Match magazine.

The US actress Uma Thurman "was an inspiration to me", Adjani admits in yet another cover story, in L'Express, this week. Her Siberian husky blue eyes and pale pink cleavage illustrate the magazine's "Investigation into Infidelity" - a sure seller in the slow summer season.

Thurman was married to the actor and director Ethan Hawke, Adjani explains. "He cheats on her with a model... She forgives him. He cheats on her again. This time, it's no. She tells the magazines it's over, that she's leaving, and he learns it through the press." Adjani's previous great love, Daniel Day Lewis, sent her a fax to tell her he was leaving her.

This time, Adjani beat her partner to it, telling Match that she had "irrefutable proof" of Jarre's infidelity. "Of course he denied it, before confessing," she said. "I think he's sincere when he lies... Jean-Michel had explained to me that it was impossible to spend a single day of vacation with me this summer, whereas he'd planned a trip to Sardinia with his future new companion."

The French actress admits that her own behaviour in baring her soul to Match and L'Express "is absolutely un-French". Her compatriots are hypocritical about such things, Adjani says. "I'm a public figure," she told Match, justifying her decision. "It's up to me to take the initiative to explain things. It's my responsibility."

But despite modelling herself on Uma Thurman, Adjani does not approve of what she calls American "sexual puritanism". It was disgraceful to try to drive the former US President Bill Clinton out of office because he had an affair with an intern, she says: "American hypocrisy consists of thinking that everything is serious; French hypocrisy is to think that nothing is serious."

The Adjani-Jarre saga could run all summer. Looking like a 55-year-old sheepdog in jeans, Jarre and his new paramour snuggle on the cover of this week's Paris Match. Parillaud bears the slightest resemblance to Adjani, but is about 15 years younger. "Their love story... was revealed against their will," Match reports disingenuously. "They obviously have their version of the facts, but they don't want to explain it."

Jarre spent 17 years with the British actress Charlotte Rampling, whom Adjani describes as "an extremely warm woman, very British in her reserve. She suffered secretly... the despair of a woman who discovers that her husband has a double life."

If you cut through the glossy photos and sniping - Adjani implies that Jarre is "an emotional serial killer" - their story exemplifies the contradiction between the French belief in romantic love and family life and their horror of routine.

At the end of June, L'Express published a cover entitled "Marriage: A New Passion", explaining that the institution is back in fashion. After a low of 254,000 weddings in 1994, the number climbed to 305,000 in 2000. Polls show that two-thirds of the French prefer marriage to living together, and young people are overwhelmingly in favour of fidelity and commitment. When Adjani and Jarre announced they were in love two years ago (where else: on the cover of Paris Match) they promised to marry this summer.

Yet after passion for marriage, L'Express has served up infidelity, as if the two went together like a horse and carriage. The fact has not gone unnoticed chez les anglo-saxons, Adjani says. "Their equation about the French is simple," she explains. "French = baguette + red wine + mistress."

Forty per cent of French marriages now end in divorce, and adultery is the leading cause. In 88 per cent of cases, it is the woman who asks for divorce, lawyers say. The only novelty is that women, traditionally more docile and faithful, are narrowing the infidelity gap.

In the past 30 years, no contest divorce was introduced in France, illegitimate children were awarded equal status with children born in marriage, and adultery became a strictly private matter, no longer a misdemeanour. Under the 1804 Napoleonic Code, an unfaithful husband risked being charged a fine while a wife could be sentenced to up to two years in prison.

In ancient Greece, fathers, brothers and husbands were granted the right to murder an adulterous woman. Caesar Augustus tried to stem debauchery in Rome by making adultery a criminal offence. Justinian replaced the death penalty for adultery with flogging and banishment to a monastery.

In France in the 21st century, you only risk denunciation in Paris Match.