Jyoti Singh, 23, had cause to celebrate. It was no ordinary Sunday. “Happiness was just a few steps away,” says her father, Badri Singh, a labourer. He and his wife, Asha, originally from Uttar Pradesh, had sold their family land, to provide schooling not just for their two sons but also Jyoti. “Papa,” Jyoti had instructed her father. “Whatever money you’ve saved for my wedding, use it for my education.” Badri’s brothers wondered why he was wasting money on a girl.

On this Sunday, 16 December 2012, Jyoti, a name that means light and happiness, had just completed her medical exams to become a doctor. Speaking excellent English, she spent nights working in a call centre from 8pm until 4am, slept for three hours, then studied. Her ambition was to build and run a hospital in her family’s village. “A girl can do anything,” she would say.

But that evening, in Delhi, she decided to go to the cinema to see The Life of Pi with a male friend. At 8.30pm, on the way home, the pair got into an off-duty charter bus. India’s Daughter, a powerful, brave and heart-wrenching documentary made by Leslee Udwin, provokes grief and anger but also pity for the ignorance. It charts what then happened on that moving bus as Jyoti was brutally raped by five men and a 17-year-old (“the juvenile”), eviscerated, then thrown on to the street. It shows how for the next 30 days across India, women and men demonstrated on the streets of the country’s cities, calling for the equality recognised in India’s constitution but never delivered, marking what a former solicitor general, Gopal Subramaniam, calls in the film “a momentous expression of hope for society”.

“It was an Arab spring for gender equality,” Udwin says. “What impelled me to leave my husband and two children for two years while I made the film in India was not so much the horror of the rape as the inspiring and extraordinary eruption on the streets. A cry of ‘enough is enough’. Unprecedented numbers of ordinary men and women, day after day, faced a ferocious government crackdown that included teargas, baton charges and water cannon. They were protesting for my rights and the rights of all women. That gives me optimism. I can’t recall another country having done that in my lifetime.”

Protesters mark the anniversary of the Delhi gang rape of Jyoti Singh in 2012. Despite legislation, rapes are increasing. Photograph: Adnan Abidi/Reuters

India’s Daughter is broadcast on BBC4 next Sunday, International Women’s Day, and simultaneously shown in seven other countries including India, Switzerland, Norway and Canada. On Monday 9 March, actresses Freida Pinto and Meryl Streep will attend a screening in New York, launching a worldwide India’s Daughter campaign against gender inequality and sexual violence against women and girls. It begins by 20 million pupils viewing the film and taking part in workshops in Maharashtra, a state that includes Mumbai.

Each country has its own appalling bloody tally. India has a population of 1.2 billion. A rape occurs every 20 minutes. In England and Wales, 85,000 women are raped every year. In Denmark one in five women has experienced a sexual assault. Sexual assault, rape, acid attacks, murder, domestic violence, the termination of female foetuses, sex trafficking and female genital mutilation are all manifestations of male power. What is writ very large in India’s Daughter, but camouflaged in other countries where equality is more strongly embedded in law, is the low value placed on females and the determination of some men, educated as well as the impoverished, to keep women padlocked to the past.

We have the best culture. In our culture, there is no place for a woman ML Sharma, defence lawyer in Delhi rape case

“We have the best culture. In our culture, there is no place for a woman,” says one man in Udwin’s film. What is shocking is that he is ML Sharma, defence lawyer for the men convicted of Jyoti’s rape and murder. A second defence lawyer, AP Singh, says if his daughter or sister “engaged in pre-marital activities … in front of my entire family, I would put petrol on her and set her alight”.

“I began this film with a narrow focus,” Israeli-born Udwin, 57, says. “‘Why do men rape?’ I discovered that the disease is a lack of respect for gender. It’s not just about a few rotten apples, it’s the barrel itself that is rotten.” Udwin was an actress before becoming an award-winning producer. Her work includes Who Bombed Birmingham?, about the miscarriage of justice that imprisoned the Birmingham Six, and East is East. For India’s Daughter she spent 30 hours interviewing rapists including Gaurav, a 34-year-old man serving 10 years for raping a five-year-old. “He told me in minute detail what he had done. How he had taken off her knickers. How her eyes were wide with fear. How he had done it front and back. I asked him how tall she was. He stood up and put his hand above his knee. I asked him, ‘How could you do something so terrible that would ruin a child’s life?’ He said, ‘She was a beggar girl, her life was of no value.’” Udwin found the girl, Neeta, now aged 10, and plans to make a film about her family’s resilience and resistance. “She is doing OK. Her mother is a beggar and has put Neeta and two other children through school.”

Central to India’s Daughter is an interview in Tihar jail, Delhi, with Mukesh Singh, driver of the bus. His brother, Ram, was found hanging in his cell months after the trial. The two lived in a Delhi slum. Also involved was Pawan Gupta, a fruit seller; Vinay Sharma, a gym assistant; unemployed Akshay Thakur; and “the juvenile”, living on the streets since he was 11. They had all been drinking before going out where “wrong things are done”.

India’s daughter

Mukesh Singh says: “You can’t clap with one hand – it takes two hands. A decent girl won’t roam around at night. A girl is more responsible for rape than a boy … about 20% of girls are good.” Jyoti fought back. Singh says: “She should just be silent and allow the rape. Then they would have dropped her off after ‘doing her’ and only hit the boy.

“The 15 or 20 minutes of the incident, I was driving the bus. The girl was screaming, ‘Help me, help me.’ The juvenile put his hand in her and pulled out something. It was her intestines …We dragged her to the front of the bus and threw her out.”

Udwin, in Hindi, reads a list of Jyoti’s injuries to Singh, caused by an iron bar and multiple rapes. They include bite marks and massive internal injuries. He shows no remorse. A gynaecologist who cared for Jyoti says for months she asked herself the same question. “Why?”

Jyoti, initially given the name Nirbhaya, meaning fearless in Hindi, to preserve her anonymity, died after 13 days. Her parents, given 2 million rupees (£21,000) by the government, set up the Nirbhaya Trust to help women who have experienced violence. “We want to help those girls who have no one,” Jyoti’s father says.

The government, to quell the protest that followed her death, set up a three-member commission, headed by JS Verma, a former chief justice of India and human rights lawyer. It received 80,000 responses and delivered a landmark 630-page report in 29 days, calling for the law concerning sexual violence to be modernised, removing terms such as “intent to outrage her modesty”. New legislation failed to fulfil many of the report’s recommendations. Since then, the number of reported rapes has increased hugely, as more women come forward.

The juvenile is serving three years. Two of the convicted men are appealing against their sentence, a process that could take years. The judge said they should hang because “this is the rarest of cases”. Except that it isn’t. It is one of many. Just over two years after Jyoti’s rape, a woman was raped by four men, beaten, her eyes gouged out. Jyoti’s father, a man of shining integrity, says of his daughter: “In death, she lit such a torch … whatever darkness there is in this world should be dispelled by this light.”

Storyville – India’s Daughter, BBC4, Sunday 8 March, 10pm