Thirty miles west of the Taj Mahal, on the road to the pink city of Jaipur, tourists on buses pass a sight that the guide books rarely mention.

	In pictures: 14-year-old's virginity for sale

A mile beyond the town of Bharatpur in Rajasthan, where the highway is being widened to four lanes, traffic slows down for roadworks. But the workmen who lounge by their bulldozers have their eyes on something else - a cluster of makeshift shelters where girls, several under 18 and at least two younger than 15, can be seen strolling or sitting, in view of the dusty carriageway.

Tonight, one girl in particular is attracting attention as she sits on a stool by a fire so that she can be seen by passing vehicles. Her heavily made-up, striking face and beautiful pink sari make her look as if she were on her way to a party. But the truth is different. Suli, 14, is a virgin and a bidding war is being held for the right to be the first to sleep with her.

The collection of shelters where she lives houses 59 families, all members of the Bedia tribe, which has a long tradition of caste-based prostitution. Girls born here become prostitutes in a rite of passage into "adulthood" as routine as marriage is to the rest of Indian society.

The "first time" is a valued commodity for which the middle-class businessmen who pass this way are prepared to pay a premium.

The normal rate is 100 rupees (£1.30) but a virgin is sold to the highest bidder for anything over 20,000 rupees. If she is very pretty, the community would hope to get up to 40,000 rupees. For this, the man can have access to the girl for as long as he likes - several hours, days, or even weeks. When he tires of her, there is a celebration. Because it is considered unlucky for a girl to keep the money from her first time, it is spent instead on an extravagant party. Jewellery is bought for her and for her relatives, goats are slaughtered and alcohol runs freely. There is dancing, and offerings are made to the gods.

Once a girl has lost her virginity she cannot marry. The choice has been made and the community celebrates it - this is her non-wedding night.

	Bidding war: Nita [left] is so pretty that a 'client' may pay £600 to take her virginity, say her sisters

Suli said she was happy to enter the trade. "I chose it," she said, though she admitted being "a little" frightened. "I do not know how it is going to be. I know other girls who are in the trade but I have not asked them how it is."

She claimed it did not matter what the man looked like. "I will go with whoever pays the highest price," she said, before running off as her mother called her for supper.

Nita, a virgin in the hut next door, has four sisters, all prostitutes. She wears jeans and a skimpy top, and giggles a lot. One sister boasts that as Nita is particularly pretty, they hope to get 40,000 rupees (£600). "We have been offered 25,000, but it is not enough."

Nita is only 13 but has opted to follow her sisters into the trade. It is her own "choice", because, she giggled, "I won't have to do any housework."

But in avoiding making chapatis, Nita has signed up to a life in which she will deal with 20 to 30 clients per day, until she reaches her forties. After that, when she is no longer considered desirable, she will depend on any children she may have for support.

Two of her sisters, Ritu, 35, and Manju, 25, have built one of the few stone houses in their village, for which they paid the equivalent of £14,600, and are proud of their success. "There was a lot of poverty, we had nothing to eat," said Manju. "What you see now has come with hard work." They support 50 family members - 35 children and 15 adults.

Elsewhere in India, the birth of a boy is celebrated with dowries paid by the bride's family, one of the reasons given for the high abortion rate for female foetuses. But in the villages around Bharatpur there is a shortage of girls to marry, and the custom is for the boy's family to pay the girl's family a large lump sum before the wedding can take place.

Possibly because the money comes from prostitution, and because any granddaughters will be destined for the trade, the sums are high.

Ritu and Manju paid for four of their five brothers to marry, and now support their sisters-in-law, nieces and nephews.

They earn between 1,000 and 1,500 rupees a day. It was more before the government knocked down their shelters to make room for the highway.

"We need a shelter by the road," they said. "Tell the government to build us somewhere we can work. We used to have 25 or 30 clients a day, now the average is 10 or 15." They said they were able to keep their rates up because they could provide a nice room and running water for their clients, who are mostly married businessmen from Agra.

The prevalence of caste-based prostitution in certain tribes in the region - the Bawaria, Nuts, Bedias, Kanjars and Sansis - came to light after a raid on a brothel in Delhi. Now an attempt is being made to break the cycle by which the girls of each generation enter the trade.

Dr KK Mukerjee, a social work professor at the University of Delhi, who was commissioned by the government to research the scope of prostitution, has founded a group, known as GNK. Supported by Plan International, a child-centred community development agency, the organisation has set up a hostel to look after prostitutes' children.

Many of the women said they did not wish their daughters to follow them into the trade. Ritu and Manju each have a daughter, whose fathers were clients. "My daughter will get educated, and not enter this profession," said Ritu. "I have seen what it is like. I don't want it for her."

A young boy at the hostel told proudly how he had persuaded his grandmother not to push his aunt into prostitution. "My grandmother said that she would kill herself if my aunt did not go into the trade and earn money," he said. "But I persuaded her, and my aunt got married."