Late at night, a makeshift temple is being erected within the stone walls of an urban dwelling in the city of Birganj, just minutes away from the Nepalese border with India. Pearls of sweat hang on Gayatri’s brow as she chants and prays over the Hindu offerings - sandalwood paste, incense, a lamp, fruit and flowers. She and the pundit (priest) make one last offering of grain before the groom, Parbhu, joins in the rituals that will last until the early hours of the morning. Blinded by her veil, Gayatri is led through each rite by the matriarchs of her family, who huddle around her.

Finally, with their clothes tied together, signifying a lifetime bond, Gayatri and Parbhu are pronounced husband and wife. Though Parbhu is 18, his spouse is just 11 years old and has had a mere two years in school; she is almost literate enough to read the Nepalese law prohibiting child marriage. Within a month of the ceremony, the marriage will be consummated and Gayatri will assume full responsibilities as Parbhu’s wife. Gayatri’s family is so poor her mother spent the wedding day begging for donations for the dowry. But as Gayatri will begin living with her husband immediately, there are financial benefits. The marriage will not only secure her future, it will rid the family of the economic burden of providing for her.

In India, the killing of unwanted infant girls is being replaced by foeticide as women who discover they are pregnant with a girl terminate the pregnancy - even though sex-selective abortion is illegal. The same prejudices exist towards girls in impoverished rural communities in Nepal, where abortion is illegal and carries a heavy sentence. On both sides of the border child marriage is still a common way of shifting the economic responsibility for females from father to husband.

In India the problem is most widespread in the populous northern states of Rajasthan, Madhya Pradesh, Uttar Pradesh, Bihar and West Bengal, which have a combined population of about 420 million, roughly 40 per cent of all Indians. A survey of more than 5,000 Rajasthani women conducted by the national government in 1993 revealed that 56 per cent had married before the age of 15; of those, 14 per cent had married before they were 10 and 3 per cent before they had reached five.

“Child marriage is an accepted tradition, a cultural practice,” explains Jyotsna Chatterjee, director of the joint women’s programme in New Delhi. “A girl is considered property that must be kept in the parents’ home until she reaches puberty and is able to become a wife and give birth to a boy.”

In India the legal age of marriage is 18 for girls and 21 for boys. Child marriage carries a prison sentence of up to three months, and a fine. In Nepal the same minimum ages apply, and violation of the law can result in a prison sentence of three years and a fine of up to pound;48 - in a country where 38 per cent of the population live on less than 60p a day. As in India, however, the law is rarely enforced and bal biwoha (child marriage) continues: around 7 per cent of girls marry before they are 10 and 40 per cent before 15. Nepal is the only country in the world where the life expectancy for women is less than that of men, and early marriage and childbirth are the two main reasons.

“The law ensures that boys will have more time to develop themselves before entering into married life,” says Narendra Kumar, a lawyer in Kathmandu, the capital of Nepal.

“Psychologically, everyone has made up their minds that the boy must be better than the girl in every way,” says Dr Rajyalakshmi, a sociologist at New Delhi University. Moreover, he says, the better educated a girl is the more difficult it is for her to marry. Because girls are seen as guests in their own homes and education is an investment that will only make it harder to marry them off, there is little incentive to provide them with life skills that will be of use outside the home.

Samphe Lhalungpa, head of the child protection and education section at Unicef in Nepal, says: “In some places, if you promote girls’ education the families will say ‘Why should we water our neighbour’s trees?’ The girl is seen as staying only temporarily. Her real home is her husband’s house.”

Although there is a school in the village of Mandalya, an hour’s drive from Jaipur in Rajasthan, none of Ramphl’s four daughters has received a day’s education. Ranging in age from six to 14, the peasant farmer’s daughters were all married in a joint ceremony on the night of Akha Teej (usually in late April or early May), the day of the year judged most auspicious for weddings by astrologers. In the run-up to Akha Teej, villages, towns and cities across the state take on a holiday atmosphere as guests flock to the big wedding tents where the mass ceremonies take place.

Marrying one’s daughter in the Hindu religion is traditionally considered one of the holiest of mortal responsibilities, and ancient holy laws (shastras) say the girl has to be married before she reaches puberty, otherwise her father has failed in his duties.

Legend has it that the tradition goes back to Muslim invasions of 1,000 years ago, when unmarried Hindu girls were raped or kidnapped; Hindus responded by marrying off their daughters as soon as possible to protect them. The story has taken on a modern twist with the widespread fear that unmarried pubescent girls will suffer similar sexual violence at the hands of men who believe having sex with “pure” girls can cure them of sexually transmitted diseases, including Aids.

These days child marriage has more to do with economics than faith or superstition. Girls are an economic burden on their families, and the financial incentive of the dowry is attractive to the families of the grooms. The marriage in Birganj of 10-year-old Ashok Ram, who has one year of schooling, to eight-year-old Kanti, who has never attended school, guaranteed his family a bicycle, a television, a watch and 35,000 Nepalese rupees (pound;314).

“People are still guided, to some extent, by their own practices and by what they consider right for their own families, for their daughters and sons, especially given their economic circumstances,” says Samphe Lhalungpa. “That is the challenge: how do you bring the two - custom and law - into alignment?” Jyotsna Chatterjee says the acceptance of the dowry system and complacency about child weddings have created conditions under which girls are sold under the guise of marriage, with pimps and traffickers staging false marriages to procure girls.

Fatima, 14, who lives in a slum in Delhi, can’t wait to move to the country. “Delhi is so dirty, so polluted,” she says gleefully, imagining what her new life will bring. Within the month her “groom”, 11 years her senior, will come to take her away.

According to Stop, a non-government organisation that rescues trafficked girls, her situation is typical of those at risk of being sold into bonded labour or prostitution. Fatima suspects nothing. Her father is a rickshaw driver and the groom is a distant relative, but her family is not paying a dowry. Instead, the groom is paying them, which was a deciding factor for the parents in allowing the “marriage” to go ahead.

The joint women’s programme believes that only an unambiguous act of parliament banning child marriages can begin to address the problem. “We have given a drafted law to the Department of Women and Child Development, the National Human Rights Commission, and the National Commission for Women, who have all endorsed it, but so far parliament has done nothing,” says Jyotsna Chatterjee. “We must protect these girls. Let us allow these girls to survive. Let them participate in their own decision-making.”

But only when law enforcement is combined with a change in attitudes towards education and vocational training will things improve. And the burden of poverty will not be lifted by new laws. “If we are able to create a movement for the education of girls, that will have a knock-on effect on the practice of child marriage,” says Samphe Lhalungpa, “especially if we say that girls must get quality basic education, sustainable literacy and a range of life skills. If girls do not have this and go into early marriage, it reinforces their subordinate status.”

Once a girl is seen as a person who can contribute financially to her own family, rather than as an unpaid servant to someone else’s, the need to marry off young daughters will disappear. Unicef’s communications officer for India, Geeta Atherya, says that in certain areas industrialisation is breaking down gender bias, with girls being trained to work in factories. “The parents there are not interested in getting the girls married because they are earning money for the family,” she says. “That could be an incentive, to get the girls into vocational training of some kind, where they are actually earning money.”