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."