Years ago, a distressed young woman walked into Dr Mahinder Watsa's clinic in Mumbai. She was not unwell, just sick at heart. Her parents had arranged her marriage. She liked the young man but she was terrified about her wedding night. As a child, she had been sexually abused by a male relative. What would happen when her husband discovered she was not a virgin?

"He will throw me out and my parents will die of shame and I will be ruined," she said. "What do I do?"

Watsa was an obstetrician and gynaecologist. What the woman needed was advice and counselling "but there was no one I could refer her to", says the doctor. "There were no counsellors in India then who could deal with these problems. So I took it up myself."

That decision, taken in the mid-1970s, proved to be a good career move. More than three decades later, Watsa is a household name in the city, thanks to his hugely popular Ask the Sexpert column, which appears in the Mumbai Mirror tabloid. In the column, he answers readers' questions about sex in an inimitably terse, direct and witty fashion.

"Every month, he gets about 8,000 queries. He's vastly popular, not just because he is upfront and direct about sex, which is unusual in India, but because he is very practical," says Meenal Baghel, the editor of the Mumbai Mirror.

Baghel says she relishes her occasional lunches with Watsa, a dignified and elegant gentleman, because that's when she gets to hear the stories that cannot be published in a family paper.

Watsa took up sex education and counselling not only to help people but also to address the shocking ignorance among Indians about sex. In this highly conservative society, sex is enjoyed - witness the 1.2 billion population - but any discussion of it is regarded as obscene.

"I was upset at the unhappiness caused by sexual problems and the fact that people had no choice but to go to quacks who gave them silly potions and even sillier advice, such as sleeping with a virgin to cure themselves of sexually transmitted diseases," he says. "I also saw that sexual problems were behind a lot of marital conflict."

In 1976, he organised what he says was the first residential work-shop on human sexuality in Asia, in New Delhi, the Indian capital. After that, there was no looking back. Countrywide training programmes for sex counsellors followed.

Today India has numerous sex experts but Watsa was in the vanguard, talking openly about the subject in magazines and newspapers at a time when Bollywood films used to cut away from a couple about to kiss and show shots of bees and flowers instead, so prudish were attitudes towards public displays of intimacy.

Even now, married couples rarely hold hands in public. Kissing in public is out of the question. Showing cleavage is not acceptable, except among a tiny overseas-influenced elite. Foreign female visitors to religious pilgrimage sites are ordered to cover their arms. On television recently, censors bleeped out the word "period", even though it was being used by a schoolgirl talking about a class, or lesson.

Watsa, by contrast, has always been open about sex. Nothing surprises him any more. At 89, he has had to scale back a bit, though - his clinics now last just a couple of hours each, every morning and evening.

As a man well qualified to talk from experience, Watsa says that when it comes to sexual behaviour much has changed - and much has not.

"I'm fed up with it. It shows no sign of letting up. The letters and e-mails keep pouring in from men who masturbate, or have masturbated at some point in their lives, and fear terrible consequences," he says.

Sitting in the living room of his Dadar West flat, overlooking the Arabian Sea, where he has lived since he was a young boy, he pulls out huge ring binders bulging with cuttings, all of which deal with that one topic. "Will masturbation make me infertile?" "Will it cause pimples?" "Will it make me impotent?" "Will it make hair grow on the palms of my hands?" "Will it lead to weakness?" "Will it stop teenagers growing?" And even, "Will it make me go mad?"

"I tell them it is totally harmless and normal," he says. "But it comes back to haunt them at different stages of their lives. When they are married, it is, 'Will I be able to have children if I masturbated when I was young?' When they get older and their erections weaken, it is, 'Is this because of my earlier bad habit?'"

The neurosis, which lurks in many a male mind, can be traced back to the deep-seated Hindu belief that semen has magical properties. According to the myth, each time semen is "wasted", the body and mind are made weaker, and the former is deprived of a "life force"; whereas well-preserved semen produces male children.

Watsa is fed up with telling patients that this is all nonsense but the conviction that preserving semen is the elixir of life remains. Mahatma Gandhi, famous for sexu-ally experimenting with young women to test his celibacy, must take some responsibility for validating this belief, which has also been propagated by Hindu ascetics and spiritual leaders. The independence activist wrote about how he used to sleep with his 19-year-old grand-niece to practise sexual forbearance and retain his semen. Any number of Hindu websites contains articles that state it takes 80 drops of blood to produce a single drop of semen.

The even stranger side to this irrational obsession is that when it comes to other bodily fluids, Hindus are obsessed with ejecting them from their bodies, which explains the noisy hawking, spitting and preoccupation with metronome-like bowel movements much in evidence across India.

A humanist to the core, Watsa is devoid of prejudices against women. On the contrary, he works to help them escape the consequences of the misogyny that is widespread in Indian society - as seen in the high numbers of rapes, dowry deaths and female feticide. Indian brides (with the exception of members of the Westernised elite), for example, are expected to be virgins. If they show the slightest carnal knowledge, in the way they move or touch their husband, during the first act of love-making, the husband will be suspicious.

"A man who had no sexual experience married a woman who happened to have received some basic sex education at her Catholic school," Watsa says. "The first time they made love, neither had any idea what to do. So she made a suggestion. He was so horrified that she seemed to know about sex that he divorced her."

For decades, Watsa has received cris de coeur from women who are not virgins but are about to get married. Traditionalists despise him for advising these brides-to-be to sprinkle a few drops of blood on the bed sheets on their first night.

Women also get a raw deal when it comes to conception. If a couple cannot conceive, it is always the woman who is blamed, a prejudice deeply rooted in the culture.

"I had a 28-year-old woman from a rural background with no child. I told the husband to get a sperm count done. Before he could do it, she jumped into a well because the family kept blaming her," says Watsa. "It's only when men remarry, after divorcing their wife for so-called infertility, that they realise it's their problem, because they can't conceive with the second wife either."

Unsurprisingly, the gentle and softly spoken doctor is a victim of hate mail. There are currently two complaints registered against him with the police, alleging that he is corrupting the young and propagating indecency. In a country where sex education remains largely unheard of, taught in some private schools but not in most government schools, the PowerPoint presentations, complete with images, he uses to train sex counsellors horrify conservatives.

Watsa has had tomatoes thrown at him and he has been accused of being a pornographer.

While many aspects of sexual behaviour in India have remained static over the past few decades (worries about penis size coming a close second to those about masturbation), others have changed. For example, women are more willing to consult Watsa, he says, either on their own or with their husband; more homosexuals are coming out; more married women are unabashed about satisfying their sexual needs; older couples are seeking to continue their sex life; and online pornography has emerged as a new source of unhappiness.

"When the husband is too absorbed in porn, watching it whenever he can, he isn't interested in having sex with his wife because it doesn't live up to his expectations," says Watsa. "They can't get aroused with-out looking at porn and their wives become boring to them. It's a growing problem."

In terms of his writing style, Watsa could teach many journalists a thing or two about economy of expression, as the following exam-ples demonstrate:

Q: I am a 20-year-old man. If I have sex with a married woman and ejaculate inside her, will it create a problem for me?
A: It might create several problems for you. For one, her husband will be after your blood. She may also get pregnant with your baby. If she is infected with a disease, you might contract it, too. I hope she doesn't blackmail you later. Also you'll be easily caught; neighbours are good at snooping.

Q: I am 45 years old and my wife is 41. My wife has never allowed me to have sex with her during the day, only at night. How do I convince her to have sex during the day, too?
A: Learn to negotiate a deal with her, or buy dark curtains.

Q: To stop my girlfriend getting pregnant, I drop some lemon juice and salt onto her vagina after intercourse. Can you tell me if this works?
A: Are you a bhel-puri [a roadside snack] vendor? Where did you get this idea from? Use a condom instead of a condiment.

Asked why his manner is so terse, he replies: "Who wants to read a tome? I want to educate but I don't want to bore. One should never make sex boring."