Ngawang Sangdrol was just 13 when she was first imprisoned by China in Tibet. She was so small her prison guards found it easy to pick her up by the legs and drop her, head first, on to the stone floor of her cell.
They beat her with iron rods, placed electric shock batons in her mouth and left her standing in the baking heat until she collapsed of exhaustion. They called her the "ballerina", because when the pain became too much for her, she would stand on the tips of her toes like a dancer. "The more we cried out in pain," she said, "the more they laughed."
"They would put a rope around your neck, tie both your hands and hang you down from the ceiling. They used iron bars to beat you systematically," she says. "And once you are imprisoned there is no difference between a child and an adult and an elderly person, or between a man and a woman. All punishments and torture methods are equal for everyone."
Ngawang Sangrol, now 28, is a Tibetan nun who spent more than a decade in prison. Released shortly before a visit by the then Chinese President Jiang Zemin to George Bush's Texan ranch, she was made to sign papers promising she would never speak of her experiences in the notorious Drapchi prison.
She was critically ill after years of abuse and doctors believed she would not live long. But she has survived to tell her gruesome tale, to the acute discomfort of the Chinese authorities.
The nun was arrested in 1990 for joining a peaceful demonstration calling for independence for Tibet. She was freed after nine months, and rearrested in 1992. In an interview with The Independent, she said: "I was imprisoned for saying just two things. 'Long live the Dalai Lama' and 'Free Tibet'. For these I was imprisoned and tortured. The sufferings our people went through after the invasion are well documented: everyone seems to know about them. But people seem to think that these days our problems are over, and this is not true. I have experienced persecution at the hands of the Chinese, and I can see it continuing."
There are an estimated 200 political prisoners in Tibet, almost all monks and nuns whose only crime is to have pledged support to the Dalai Lama, the head of the Buddhist faith, who leads a government in exile in India but whom Beijing regards as a separatist threat.
The London-based human rights group Free Tibet, says torture "forms a part of these prisoners' everyday lives". Human Rights Watch reports document the "mistreatment in detention" of religious figures and activists, citing Tibet as one of the two regions in China where torture is most rife. Beijing denies this, but none of the numerous claims of torture has been investigated by the Chinese authorities.
Life outside the prison walls is also tough, say rights activists. Since direct rule was imposed by Beijing in 1950, the authorities have denied charges of restricting basic freedoms.
Ngawang Sandrol, now living in the US, is in London to urge the UK to use its forthcoming EU presidency to appoint a special EU rapporteur for Tibet and to promote negotiations between Beijing and the exiled Tibetan government.