Faduma Ali, 86, still remembers the pain of being circumcised at eight. Horrific as it was, she allowed her own daughters to go through the same ordeal. But when it came to her granddaughters, she decided to step in and stop it

"As a little girl I would go looking for the cutters and ask them when it was my turn," Faduma Ali says. "I thought it was exciting. I wish I had known then what I know now."

It's almost eight decades since Faduma underwent female genital mutilation (FGM), sometimes known as female circumcision, in Somalia. Today, sitting in her daughter's lounge in north London, she says it has left her with a lifetime of pain and medical problems. Yet despite her own agony she felt powerless to resist the societal pressure driving the tradition, and insisted her own daughters have it done too.

But when her granddaughters faced the same fate, she knew something had to change. And as an older woman, her voice carried more weight. Faduma told her daughter not to let her granddaughters be cut. "Women can eradicate this," she says. "Mothers are responsible for refusing the practice."

Campaigners say that a tangled mix of family pressure, cultural traditions and religious motivations make FGM – illegal for almost 30 years in the UK – hard to eradicate. It has been documented in 28 countries in Africa and in a few countries in Asia and the Middle East. The practice involves removing all or part of the external female genitalia (including the clitoris, labia minora and labia majora – and in some cases the narrowing of the vagina), and is usually carried out before the age of 15. As well as the risk of bleeding to death or infection, a terrifying array of physical and psychological problems can follow.

Today 30,000 girls in the UK are said to be at risk of this form of mutilation, while 66,000 live with the consequences of it. Yet no one has ever been prosecuted for carrying out or abetting the practice (which carries a maximum prison sentence of 14 years).

This, say campaigners, is because children are unwilling to speak out against their families and communities and that is why Faduma, along with her daughter, Lul Musse, and granddaughter, Samira Hashi, have agreed to explain how – even in a loving and close-knit family such as theirs – such a custom can be perpetuated.

Samira, 22, is translating for her grandmother, who explains that growing up in the suburbs of Galkayo, a city in south Somalia, being "cut" was not just something she looked forward to, but insisted upon. "Everyone had it done," says Faduma, 86. "If you didn't, you were shunned. I saw it as something exciting."

She was under no illusions about how painful it could be, however. "I saw it being carried out – most girls would try and run away. But it was part of our way of life. My grandmother and mother had had it done, so it seemed natural."

Faduma's father, who was in the Somali military, was not convinced. "He had a city attitude because of his travels," says Faduma. He told her grandmother, with whom Faduma lived, that she was not to be cut. But Faduma convinced her grandmother to take her while he was away.

The cutter had no medical qualifications and performed the operation in the open air, without sterilisation or pain relief. Faduma was eight.

"There were four of us," Faduma recalls. "But because I was the bravest I was told to go first.

"My grandmother and the other girls' mothers held me down and the woman cut me with a knife. It's like someone is cutting your finger off without pain relief. My blood was shooting into her face and eyes."

Next, the wound and her vagina were sewn up, leaving her a hole the size of a match head through which to pass urine and menstrual blood. With no medical equipment, three thorns were used in place of stitches. Yet her ordeal was far from over.

"They gave you milk and waited to see if you could urinate," she recalls. "If not, they cut you open a little more. For two weeks it is agony."

Afterwards, she says, she boasted to her friends she had been cut, but never realised it would have such severe complications. "The minute you have it done you have problems," she says. "When you have your period, it is very painful and when you have children it is very painful."

Female genital mutilation, says Faduma, was intended to guarantee virginity before marriage by ensuring sex would be frightening and painful for girls. Giving birth, however, was nothing short of torture. Faduma had 10 children, but her first labour lasted five days with midwives forced to "cut me everywhere" to get the baby out.

Yet when her daughters turned seven, Faduma could not shun the custom. "Without it, my daughters would not have been allowed to marry," she says. "There was not a girl in sight who hadn't had it done."

Now 52, Lul agrees: "You couldn't go to school without it, or people would laugh at you," she recalls. Her operation was in a hospital under anaesthetic, aged seven. "I tried to run from the operating table, but my mum and her friend held me down."

The operation, she says, had a devastating effect on her life and affected her marriage. "When you have sex it is very painful and you don't feel any pleasure. You will never enjoy sex."

Giving birth was excruciating and complicated for Lul. Yet, amazingly, this did not affect her decision to have her own daughters cut. But her mother stepped in. "I was sick of it," Faduma says, firmly. "Times had changed. Women were freer and had more power."

She told her daughter not to do it. Yet Lul says she would have rebelled had they stayed in Somalia. "I would have done it even though my mother said no. All men wanted circumcision. If your daughters weren't cut they would say they are like hookers."

She believes it is up to men to take a stand. "This has to be a man's campaign. Until men say stop, that this is not part of our religion and not part of our culture, it will still go on."

For Samira, the very idea of this kind of mutilation is incomprehensible. Brought up in London, she was working as a model when she was approached by BBC3 to present a documentary about Somalia. Visiting the war-torn country, she met women who planned to have their daughters cut and saw a six-year-old girl who had been recently subjected to FGM. "I just didn't understand how a mother who had gone through this pain could have it done to her children. I don't blame the women, I blame the society that doesn't stop it."

Since the film came out last year, Samira has been touring schools with Save the Children to highlight issues facing Somalia. "One thing I have learned is that while people may say we are moving on, it still continues."

According to Forward, a leading UK charity that campaigns to end FGM, the practice takes place in many cultures and occurs in several different religious communities. However, mainstream spiritual leaders have denied that the practice stems from religion. Samira believes the desire to control women's sexuality lies behind it.

"I think women here are scared their daughters will become too westernised and not get married – that they will have boyfriends and go out, and this is why they have it done."

Yet the subject, she says, is rarely discussed. "I go into schools with a high number of Somali girls, and they always seem shocked that it is part of our history and culture. We need women to talk about their experiences, men to talk about their marital experiences, clerics to explain it is not linked to religion and doctors to talk about the problems it causes. Then things will change – when we discuss what FGM is really doing."

• This article was amended on 9 September 2013. The original included a phrase which could be read to mean that FGM was practised within the Jewish community. That is not the case although there is some evidence that FGM was practised within a minor Ethiopian Jewish sect.