After falling in love with Osama's elder brother, Carmen Bin Ladin spent almost a decade with the Saudi clan. Her experience left her bitter, she tells Emma Brockes.

Carmen Bin Ladin and her daughters, Wafah, Najia and Noor, are the only Bin Ladins in the Western world to be listed in the telephone book. They live in Switzerland, where Carmen grew up and where she fled 20 years ago from her marriage to Osama's elder brother Yeslam Bin Ladin. I am to meet her at a hotel on Lake Geneva today, because she wants to talk about what life was like inside the bin Laden clan (she differentiates between her immediate family and the wider bin Ladens by altering the spelling of the name - her only concession to obscurity). For nine years she lived at the heart of the world's most notorious family, and the only way to exorcise this, she believes, is to spill the beans. The bin Ladens would like her to shut up, but she will not even go ex-directory.

Unsurprisingly, the lives of Bin Ladin and her children have been enormously difficult since September 11th. The hotel at which we meet is one of those sinister international clubhouses for the world's most powerful, where men with earpieces guard the door and the car park is full of Ferraris. We sit on the terrace under a mauve sky and Bin Ladin twitches and jitters, chain smoking and apologising for her English. Her father was Swiss, her mother Iranian, and she grew up speaking French in Geneva. When people walk by she lowers her voice.

Bin Ladin's book, The Veiled Kingdom, is one she would rather not have written, given the hostility it will in all likelihood generate from an already hostile family. But she wanted to explain to her daughters why she fled their father's house and, to the world, why she continues to carry his name. She also, I gather, hopes that the book will do something to alleviate the loneliness of her position; she is exiled both from the society of her husband and from polite society in the West, where the name Bin Ladin doesn't open many doors. "For 14 years I fought alone. And nobody believed me. I fought the bin Laden clan in private." This is a plea for her struggle to be recognised.

Carmen Dufour met Yeslam Bin Ladin in 1973, when he rented a floor of her mother's house in Geneva for the summer. She was already accustomed to luxury: her mother's family, the Sheibanys, were Persian aristocrats, and their life in Switzerland was awash with money. But Yeslam came from a background of staggering wealth. He was 24, a little older than she, the 10th son of Sheikh Mohamed bin Laden, one of the wealthiest men in Saudi Arabia. After they married they moved to Los Angeles, to study at the University of Southern California, and then, in 1976, Yeslam asked her to return to Jiddah with him, so he could work in the family firm: the multibillion-dollar Bin Laden Corporation, a construction company. She reluctantly agreed. "I loved my husband," she says. "That's it."

The life that awaited her in Saudi Arabia was one that her husband tried to prepare her for but that still came as a shock. They moved to Kilometre Seven, a district of Jiddah where most of bin Laden Sr's 22 wives, 25 sons and 29 daughters lived. Each wife was referred to by the name of her eldest son, so her mother-in-law was Om Yeslam - in the absence of a son a mother would take on her daughter's name - a woman who, despite being disappointed that her son had married a Westerner, was cautiously welcoming.

Bin Ladin made her first mistake minutes after stepping off the plane, where one of Yeslam's brothers had come to meet her. "Hi, Ibrahim!" she called. She wondered why he frowned so before remembering that women were not permitted to speak to men in public. She would make the same mistake, some time later and to more violent effect, with Osama.

In the meantime Bin Ladin had some fitting in to do. She writes that adapting to life as a Saudi woman was like undergoing an anaesthetic. "Only the men could come and go as they pleased. We women were confined to the house. . . . Even to go into the garden we had to notify the male employees to vacate the premises." She couldn't go anywhere without a chaperone. "We took no exercise. Walking anywhere was unthinkable. Hotels, sports arenas, theatres, swimming pools, restaurants, if they existed at all, were only for men."

And yet, she says, she had high hopes for the future both of the country and of her marriage; Yeslam was one of the more liberal of the brothers, a fact he had demonstrated while they were engaged by allowing her to smoke in front of his brothers. Breaking with custom, he also asked her opinion before making decisions and groused to her about the inefficient workings of the family business.

The life she led was subtly superior to that of her sisters-in-law: she didn't wear a veil when travelling by car, she held tennis parties at the house, she smuggled in banned books from trips to Switzerland (the bin Laden name ensured her luggage was never searched) and she was permitted by her husband to instruct the carpet fitters on what she wanted for their front room. (They threw a fit at being spoken to by a woman and went straight to Yeslam, who backed his wife.) She won a major feminist victory by crossing the road unaccompanied. Meanwhile, pineapple chunks were introduced to the kingdom and the first Safeway opened in Jiddah. Things were looking up.

And then she met Osama. He was a student at King Abdul Aziz University, in Jiddah, and when she opened the door to him he freaked out. Her face was uncovered. Osama started flapping his hands and wouldn't come in until she had made herself scarce. She met him only a couple of times after that, and while his zealousness was extreme he did not seem remarkable to her, either within the family or the wider Saudi culture.

"He was very religious, but he was not the only one being that religious. He had other brothers who were that religious. Some of the other brothers seemed more Westernised, like my husband, but deep down their beliefs were closer to Saudi Arabia than the Western world. Deep down this was their way of seeing."

Contrary to her expectations the country never did liberalise, and it wasn't until Bin Ladin had her second child that she began to exhaust her husband's liberal streak. He resented the way she was bringing them up. He told her the children were not permitted to celebrate their birthdays, as this was a Christian affectation. He made no attempt to assuage his wife's concerns about what would happen were he to die: in Saudi culture the widow is bequeathed to her husband's surviving male relatives.

They lived in palatial splendour - she cattily remarks that the bin Ladens have no taste in interior decor, all gold taps and terrible paintings - and it wasn't unusual for Yeslam to give her €40,000 to go out shopping with. But he started to exclude her from his decisions, and after a fall-out with his brothers he struck out alone and made another fortune - she puts it at €250 million - when he set up Saudi Arabia's first brokerage firm.

The deranged double life they led wore her out; one weekend she and the girls would be waterskiing in France, the next encased in black cloth, virtual prisoners in their own home. "There was always a part of me that kept worrying about the future of the girls. I sometimes wonder whether I'd have been so observant if I had had two boys. You see? My main responsibility went to the future of my daughters."

As the marriage disintegrated she started to think about getting out. "I didn't know any other foreigner who was married to a Saudi who was able to keep her children and bring them up." There was, she says, an underground network that smuggled women out of the country on fake passports, a relatively easy feat given that the men in the passport booths were not permitted to look under a woman's veil to check her appearance.

Luckily, Bin Ladin had kept her Swiss passport, and in 1985, on a trip to Geneva, she informed her husband thatshe had no intention of returning to Saudi. They lived together in Switzerland for a while and had a third daughter, but the marriage was effectively over, and in 1994 Carmen started divorce proceedings. They are still going on. She says her husband, who to her horror was given Swiss citizenship, refuses to acknowledge his daughters. For a while she kept in touch with some of her sisters-in-law in Saudi, but they have been silent since September 11th.

When news of the attacks reached her, says Bin Ladin, she thought immediately of her brother-in-law. She hadn't spoken about him with her husband since 1994, when Yeslam told her that Osama was in Sudan. But she had followed his activities in the press, his connection to the first bombing of the World Trade Center and that of the US embassy in Tanzania. "And when the second plane hit I knew that their name would be involved."

All of which makes it so strange that she should choose to hang on to the name. "I discussed it with the girls and we realised very deeply . . . we came to the conclusion that, unfortunately, the name is too well known, that people would just say, oh, in reality she is a bin Laden - she changed her name. Like people still talk about Hitler's nephew changing his name. There is no escape. The best thing is to face it and to explain that we are Westerners carrying the name. We fought to gain our freedom; the truth always comes out."

After the attacks the phone more or less stopped ringing. All four of them lost friends. They couldn't get bookings in hotels or restaurants. Some months before the attacks her eldest daughter, Wafah, had returned to Switzerland from the US, where she'd studied law at Columbia University. She decided not to go back. They have visited the US once since then, informing the US embassy in advance, so as not to cause panic at immigration when their name was read on their passports.

Wafah is 26 and finding it hard to get work, as is her 24-year-old sister (the youngest is still at school). "It is understandable," says Bin Ladin, "that an employer may worry whether his clients will be offended that he has hired a bin Laden. The situation is very complicated, and I don't know when it is going to clear up. These three girls are trapped. It's a fact they carry a name, it's a fact they have values that don't correspond to that name."

They have been totally rejected by the bin Laden clan. "When they come to Europe they don't even call. Since 9/11 not even their father has called to see how they are coping with this situation." And she is unconvinced that they have cut off all ties with Osama. "They have never condemned Osama. They have condemned the terrorist act. But they have never admitted any involvement of their brother in those acts. He has sons in Saudi Arabia who work at the organisation. When my mothers-in-law used to speak of him, especially after he had gone to Afghanistan, it was with pure admiration. They respect his faith."

The life Bin Ladin lives in Geneva is not a happy one, but where, she says, can she go? She feels as if she has been fighting for a very long time. She is tired but hopes her resources will outstrip those of her husband and his family. "You cannot change, you cannot hide, you have to face it. Our only way out is to explain. We stand, and this is how we are." She puts her hands over her eyes. She is shaking. "I am sorry." ... - Guardian service

The Veiled Kingdom by Carmen Bin Ladin is published by Virago, £10.99 in UK