Esther is a softly spoken young woman who is rather reluctant to talk about herself. She is currently living quietly, going to college and looking after her baby son. But she has already experienced more in 19 years than most people do in their entire lives. Her childhood, in Freetown in Sierra Leone, was happy enough. "I had a nice life with my brothers and my mother and father," she tells me when we meet in her tiny flat in a large estate in Hackney. "The only difficult thing I had to face was that my aunts used to come from the village to see my father and tell him it was time for me to join the secret society. That meant that it was time for me to be cut, to be circumcised."

In Sierra Leone, the vast majority of girls undergo this practice. Genital mutilation can involve different procedures in different places - in that country it includes the removal of the clitoris. "My father would give them excuses, and say he would bring me one day," Esther goes on. "But he didn't want me to go, he said, it's evil. We are Christian and this is not what Christians do - he had converted and his family back in the village didn't like it. He protected me and said I didn't have to do it." Esther stops for a bit, until I prompt her. "But then the war came."

Esther was about 12 when she was taken by a soldier into the bush to be his sex-slave. Many girls and young women were abducted in this way by the rebel army. "These soldiers were terrible, I saw things that no one should have to see," she says. After the war, Esther returned to Freetown, but found that all her family had been killed and that it was impossible for her to remain there. "Everyone knew I had been taken to the bush, and they shouted and pointed me out in the streets. I had to go back to the village, but I was scared because I knew that there I would have to join the secret society."

Luckily, her uncle came from America, looking for anyone who was left of the family, and said he would help her to get away - not to America, because he already had family to look after there, but to England. "He said, claim asylum when you arrive. I didn't know what it meant. But a social worker came to get me at the airport because I was all alone and I was only 15. I told them what had happened to me and how if I went back I would be circumcised. The social worker said, 'You are in England now and you don't have to do that; in England there is a law against circumcising girls.' "

Although female genital mutilation is practised in many countries, Sierra Leone is generally recognised as one of the most intractable for reform, since there the practice is so widespread and so deeply embedded in tradition. One leading Sierra Leonean activist, Rugiatu Turay, has described in a World Health Organisation report what she went through when she was cut: "They used a crude penknife, it was so painful. I bled excessively for two days and fainted when I wanted to walk. Afterwards the scar itched and got infected."

With no law against female genital mutilation and no protection for girls who resist it, Esther is afraid to return to Sierra Leone. But her application for refugee status has been opposed by the Home Office and, very unusually for asylum cases, has gone all the way to the House of Lords, which will deliver its judgment today. Although she is not in imminent danger of being sent back - she has been granted temporary leave to remain for three years on humanitarian grounds - a positive decision today would not only give her greater security, it would also be a sign that the UK might be beginning to take its obligations to women refugees more seriously.

Esther's case goes to the heart of a tense debate about what western countries owe women who come here seeking safety. According to the 1951 Geneva Convention on the Status of Refugees, which forms the basis for our asylum laws, people must be given asylum if they have a well-founded fear of persecution "on account of race, religion, nationality, membership of a particular social group, or political opinion". Because this law does not explicitly mention gender, the persecution that women face because they are women - forced marriage, honour killing or genital mutilation - is often discounted.

In Canada since 1994, in the US since 1996, and in Australia since 1997, a number of women have sought and gained asylum on these grounds; in US law it has now been described as "well-settled" that asylum should be granted if there is a genuine fear of female genital mutilation. But in the UK the situation is more mixed. Asylum has sometimes been granted to women fleeing genital mutilation, but the judgments on Esther's case show how open the refugee convention is to interpretation.

For example, Lord Justice Auld argued in the court of appeal that it is the fact that so many women in Sierra Leone accept and even carry out genital mutilation that makes it impossible to see it as persecution for the purposes of asylum law: "The practice, however repulsive to most societies outside Sierra Leone, is clearly accepted and regarded by the majority of the population of that country, both women and men, as traditional and part of the cultural life of its society as a whole." Frances Webber, the barrister who argued Esther's case in the House of Lords, cannot comment directly on her case, but is concerned by the attitudes that women asylum-seekers often encounter. "There is an institutional refusal to accept the reality of the situations that women face. There is a real battle going on. A ferocious battle." And the terms of that battle have, unfortunately, been muddied by our current fears about how many migrants western countries can accept.

But the truth is that the numbers do not rise in frightening leaps and bounds when asylum law begins to respect women's experiences. I spoke to Pia Zambelli, a lawyer from Canada, where the fear of female genital mutilation has been accepted as the basis for refugee claims since 1994. She has sat for many years on the board that oversees all asylum claims in Canada. "We didn't see an explosion of numbers of women coming with these claims. That idea is unrealistic, because so few women want to make that journey or can make that journey. We did see some - at the very outside I'd say 100 women a year, although it's probably far fewer than that."

While Esther's case is important in clarifying the way the law in the UK regards female refugees, it is also true that many women who claim asylum on the basis of a threat of genital mutilation will never see their cases considered by senior judges. This will not change if Esther wins her case - a wider and deeper change in awareness is required. For instance, a woman, whom I will call Jane, is currently living in Leeds. She left her family in Nigeria because her uncle wanted her to be circumcised before her marriage; she fled to Lagos but her family tracked her down and had her arrested and jailed. She was only released when she promised to go back to her family - but she managed to flee again and this time left Nigeria. Even though her solicitor produced documentary evidence, including a newspaper report of her family's search for her, and police records of her arrest, the Home Office has refused to believe her story. Jane has already been detained once and is now living in constant fear of deportation. "They could come for me at any time," she tells me. "What kind of a life would I have then? I know my family would circumcise me and my child. I would rather kill myself and my daughter than be sent back now."

Women in the west are often reluctant to speak out about female genital mutilation because they fear being seen as patronising and paternalistic about other women's experiences. Germaine Greer has even argued, in The Whole Woman, that "infibulation and clitoridectomy could well be as gratifying to the Somali woman as Jen Angel's dangling hardware [ie, as a western woman's genital piercings]". But this ignores the fact that female genital mutilation is carried out on children, rarely on women, and that there can be no real choice in those societies, like Sierra Leone, where a woman becomes unmarriageable and an outcast if she refuses to allow her clitoris to be cut away.

Ayaan Hirsi Ali, the Somali-born Dutch ex-politician, who herself underwent a minimal form of female genital mutilation as a child, has become one of the strongest voices speaking out against it. Although she is often painted as being anti-immigration, when I asked her if she thought women fleeing mutilation should get asylum in the west, she was unequivocal. "My answer is an outright yes," she told me on the telephone from Holland. "If women are asking for asylum, and if they are given it they will not be mutilated and if they are sent back they will be mutilated, every country that has signed the refugee convention must give protection."

But even if asylum is a solution for a few women, there are many other steps that need to be taken. Waris Dirie is another Somalian woman who was herself mutilated, at the age of five. She is now a model, and has written powerfully about the experience in her book Desert Flower: "There's no way in the world I can explain how it feels. It's like somebody is slicing through the meat of your thigh, or cutting off your arm, except this is the most sensitive part of your body . . . I will never know the pleasures of sex that have been denied me. I feel incomplete, crippled, and knowing there is nothing I can do to change that is the most hopeless feeling of all."

Dirie has become a campaigner and UN spokeswoman on the issue. She too supports the rights of women to seek protection in the west, saying that at the moment they face a "double torture": "They leave their country with great expectations, that they will find safety, and then find themselves in such a bad situation here." But she also calls on European governments to assist the African governments that have passed laws against female genital mutilation, to help them to enforce the laws and to give protection to those women who would resist the practice: "I think that every woman in the world should take a stand on this - we are all in this together. The more of us stand up for our rights, the faster the world will become a more balanced place".

· Some names have been changed.