There is a certain type of nice, middle-class Irish boy that specialises in easing the stress of a certain type of nice, middle-class Irish husband and father. The stigma of homosexuality still has such a grip on Irish men that many who are homosexual live a charade of a life. They marry, have children, follow careers, play golf and do all the things that Irish men are supposed to do, all the while living on a kind of emotional auto-pilot. They suppress their true sexuality at great psychological cost. Then, when it all becomes too much to contain, they seek a brief sexual encounter with a male prostitute. No prizes for guessing who the winner is in this situation, where a "masseur" can make between £50 and £300 per session, often seeing three or more clients a day.

Prostitution "gives me an opportunity to enjoy myself and make money", says Paul, a self-employed masseur. Men such as Paul regard their sexual contracts as being above prostitution and look down on the "rent boys" who ply their trade at the Phoenix Park's Wellington Monument and on Burgh Quay, among other places, in Dublin. "That term [prostitute] applies to those who work the streets. I'm an escort, not a prostitute," says Frank, another nice middle-class boy.

Paul and Frank were talking to Evanna Kearins, author of Rent: the Secret World of Male Prostitution in Dublin, which is published today. Evanna is a 24-year-old reporter with Today FM who investigated the male prostitution scene for her masters thesis in journalism at Dublin City University. Her undergraduate thesis was on male cross-dressing, an investigation inspired by her experience of being chased in Drumcondra in the early hours of the morning by a man in full women's regalia - including stiletto heels.

In a scene straight out of Charlie's Angels - drag-queen version - Evanna, also in heels, ran for her life and escaped unharmed but was left with a fascination for transvestites who, she later discovered, are a benign lot who rarely attack anybody. "The guy who chased me was a freak," she explains. After graduation from DCU, Evanna went into PR for two years before returning to DCU to do her masters. She wanted to do a thesis on female prostitution but her adviser, Brian Trench, suggested that male prostitution as a thesis subject would have more bite. Trench and his DCU colleague Colum Kenny recommended that Evanna get her thesis published, which she has done, receiving no advance money but the promise of royalties should the book do well.

Evanna, from Beltra, Co Sligo, has two brothers in the Garda and used her police contacts to engage with male prostitutes, both rent boys and masseurs/escorts. Her initial interviews were conducted in the safety of Cabra Garda Station, where a friendly garda brought in a male prostitute who was willing to be interviewed in the station by Evanna. And so began the process of Evanna losing her innocence. As she began to develop contacts, a gay friend took her to a well-known cruising spot in the Phoenix Park one night to show her the reality of street prostitution.

"I was very naive; I thought there were only three or four male prostitutes in Dublin. I knew it existed but didn't think it was such a big thing. I was surprised at how concentrated it was," says Evanna, who now estimates the number of male prostitutes in Dublin at 600. With the persistence of a David Attenborough, Evanna returned regularly to the Phoenix Park during daylight hours to observe the sexual habits of rent boys and their clients.

"They are not visible to someone who would not be looking out for them or unless you knew where to find them," she says. Rent boys supporting heroin habits were willing to accept as little as £5 in exchange for their services and insisted that they were not homosexual because they only gave attention and didn't accept it for themselves. To prove their heterosexuality, they also tended to talk about girlfriends.

There was no such smokescreen among the middle-class boys, who were much better educated and usually had full-time jobs in mainstream society, in addition to their lucrative sidelines in the sex industry. Rather than denying their homosexuality, they tended to classify themselves as homosexual or bisexual, and chose to become involved in prostitution because they enjoyed it.

David, who is in his mid-20s, has a "plush" two-bedroom apartment in Dublin's city centre. He's clean, good-looking and well-built with short, black hair, brown eyes and tanned skin, Evanna tells us. He spends a lot of money on clothes and is very well spoken, has a university degree and works part-time in a normal job while providing a massage service at his apartment on weekday afternoons. He's very polite and friendly, with an average, middle-class upbringing which he describes as "loving and supportive".

Although a childhood trauma - the death in a car accident of a sister when David was only seven years old, an event which David says his mother never recovered from - may hold some key to the darkness in his psyche, David himself feels that he is happy and well-adjusted and enjoys what he does because, by seeing 15 clients per week in the afternoons, he can make a lot of money: £50,000 tax free per annum, on top of his normal part-time job.

He says that 75 per cent of his clients are married: "A lot of married guys, all they want to be able to do is touch and feel another guy . . . They are generally confused about their sexuality. "This generation is changing and it is becoming easier to be gay, but in the last generation everybody got married . . . At the end of the day, most gay guys can perform with a girl. Even I have been with some girls . . . I have a lot of regulars whose sex life with their wives has failed to satisfy them, and I know there are a lot of frustrated women out there."

Evanna listened neutrally to such confessions and reported them without judgment in her book. Rather than analysing her subjects, she was left with more questions than answers about the male prostitutes, who "infuriate gardai, confound psychiatrists and bewilder legislators".

Calling for Ireland to confront this invisible profession, she believes there is a need for a single agency with the power, resources and ability to respond effectively to the diverse experiences and needs of men involved in prostitution.

In the end, she takes a moral stand and states that male prostitution should be prevented, but that those already working the streets as rent boys deserve an outreach service. "I feel the greatest amount of sorrow for street prostitutes and I wish I could do something for them, but I don't feel bad for the off-street prostitutes, who are in control," she says.

Did the whole experience change Evanna? "I would believe anything now in terms of what is happening out there," she says. "I've become much more open to what is going on and more receptive. More observant. Eyes opened. I've left a bit of naivety behind that I'll never find again, but I think that's a good thing."

Rent: the Secret World of Male Prostitution in Dublin by Evanna Kearins, is published by Marino today. £7.99