There was a moment when Claudia, as a young gay man living with the person she describes as the love of her life, was "blissfully happy". Now, approaching 50 and medically retired from her successful career as an opera singer and performer, she is full of regrets. "I feel I was railroaded into having a sex change," she says, "when I should have been enabled to live happily in my own skin."

Claudia, who does not wish to reveal her surname, is one of a growing number of male-to-female transsexuals who regret undergoing gender-reassignment surgery. In 1985, after a consultation with psychiatrist Russell Reid that she says lasted only 45 minutes, she was diagnosed as transsexual and referred for surgery. Reid, until his retirement last year, was the UK's best-known expert in gender identity disorders (GIDs). During more than 20 years of practice, Reid was responsible for assessing whether those wishing to change sex fitted the criteria for treatment. On Monday, after a case lasting three years, the General Medical Council's disciplinary committee ruled that Reid had prescribed hormones to five of his patients too soon, and referred them for genital surgery without properly assessing their mental and physical suitability.

The complaints were made by four doctors at the gender clinic at Charing Cross hospital based on the cases of five male-to-female transsexuals. Claudia was keen to be a complainant, but the GMC ruled that due to minor inconsistencies in her recollection of the consultation with Reid 20 years previously, and because they had sufficient witnesses with similar complaints, she would not be included in the disciplinary case against Reid. She is, however, currently pursuing a civil claim for damages against him.

Growing up in a tough working-class neighbourhood in the east end of Glasgow, Claudia was, she says, constantly reminded of the worst aspects of manhood, and had no desire to become like the men she encountered every day.

"The women wore the trousers in my family," she says, "with my mother and grandmother keeping things together." The men in the neighbourhood, meanwhile, "battered each other, got drunk, and molested children". Anything less than macho and violent, recalls Claudia, and you were not considered a "real man".

From primary school onwards, Claudia was bullied for being effeminate, and called a "he/she". "I grew up believing I could never live my life as a 'real' man. I never for one moment thought I was a little girl trapped in a boy's body; I just did not want to be the sort of boy I was expected to be."

Claudia was "terrible at all sports", had no friends and felt totally segregated. "I was battered every single day at primary school, and it only got worse at secondary school," she says. "I learned all about the rage of young men, and the last thing I wanted to do was become one."

By the time Claudia had her first real relationship, she was 18 years old and very sexually inexperienced. She met Martin (not his real name) in 1976 when she was at hairdressing college and he at Strathclyde University.

"He was beautiful," Claudia recalls, "like a cross between Jesus and George Best." They soon became lovers and moved in together in Glasgow. Martin, however, insisted he was heterosexual and referred to Claudia as "a woman with a penis."

Claudia had begun to dress as a woman in order to stop the homophobic bullying she endured on a daily basis. "I looked so androgynous," she says, "I had two choices. One was to butch up, the other to dress as a woman."

With Martin as her manager (he was from a family of musicians), Claudia's love of singing and performing became a lucrative career for them both. In her early 20s Claudia began touring abroad with her show. She soon found that her days of being bullied for her appearance were not over. On her way from Paris to the Hague, a border guard took exception to Claudia dressing in a feminine manner when her passport confirmed she was male. "He had a wobbly, and really battered me," says Claudia. "When I got home Martin said we had to 'fix it' once and for all."

Under increasing pressure from Martin, who insisted Claudia was "really a woman", she decided to undergo hormone treatment as a first step in the direction of a complete sex change.

Having been prescribed hormones by a psychiatrist in Glasgow, Claudia began to live as a woman, just before moving to London with Martin in 1985. Hearing from friends in the close-knit transsexual community that one of the only surgeons who carried out gender-reassignment surgery was about to retire, she made an appointment with a psychiatrist to whom many of her friends referred as "Uncle Russell" - Reid - who was then based at Charing Cross.

Claudia says that during the 45-minute consultation, Reid asked her how she was earning her living; how long she had been taking hormones; and whether she had played with dolls as a child. Claudia explained that her life was bound up with her boyfriend, who was also her manager. She told him she wanted to change sex because she was living with a man who was not gay and that he was having affairs with women.

"Warning bells should have been ringing for him there and then," says Claudia. "Even I was aware at the time that those reasons weren't good enough." However, Claudia was convinced her troubles - with bullying, and her relationship with Martin - would be over if she changed sex.

"Martin slept with women the whole time I was with him," says Claudia, "and would say, 'If you were a girl, this wouldn't be happening,' and of course I believed him." A year after the surgery, Martin left Claudia.

"If I had been properly assessed, it would have been obvious that sex-change surgery was inappropriate for me," says Claudia. "I was desperately unhappy and was going for a sex change because I felt under pressure from my boyfriend." No searching questions were asked about her background and no warning or preparation were given as to the impact of such life-changing surgery. That surgery took place just three months after her consultation with Reid.

Since the case against Reid began, many in the transsexual community have spoken in support of him. Websites serving the gay and transgender communities are full of comments about how Reid has shown phenomenal support to numerous transsexuals. He "has saved the lives of many trans people, treated them with respect and left them with the dignity they deserve," reads one post. Many others wrote in, agreeing.

Claudia's world, however, began to crumble soon after the surgery. "My body was not my own any more," she says, "and it turned out not to be the success I had been led to believe it would be, in more ways than one." She found sex difficult, as the surgery had not been entirely successful. In pain and discomfort, her confidence was at rock bottom and her desire for sex nonexistent.

Soon after her change, Claudia became sucked into the world of transvestism and transsexualism, even though it felt "alien" to her. "I was by then a very successful opera singer and drag performer," she says, "but as soon as I had my surgery I lost all confidence. Rather than going on stage in character, I was there as this thing. There is a huge leap from being a cross-dresser to being a transsexual."

When Claudia's relationship with Martin broke down, so did her professional and home life. Soon afterwards, she suffered a breakdown. Claudia moved in with her mother in Glasgow, and it was then that she first sought help for depression. "Before the breakdown I was in total denial that the cause of the problems was the sex-change operation and its consequences."

In 1995 Claudia suffered a sexual assault, an event she found deeply traumatising. At first police, not realising Claudia was a transsexual, were sympathetic. When the forensic examiner realised, however, everything changed. "Policemen would come into the room I was in, just to have a look at me. Some would laugh. It was then that they stopped taking the attack seriously. "It was during her recovery that Claudia had the opportunity to reflect further on how drastic a mistake it had been to have sex-change surgery to correct her psychological problems.

After reading the novel The Silence of the Lambs, which includes an account of a man who wanted to have a sex-change operation but was not referred for one because he did not meet all the criteria, Claudia realised that she had not met them either. "It was only on reading that book that I realised that there were any criteria in place for assessing patients for sex change," she says, "and that psychiatrists had to take account of these before referring somebody for such a drastic life-changing operation."

Before being prescribed hormones, patients seeking to undergo gender-reassignment surgery should be able to display demonstrable knowledge of the effects of hormones on the mind and body, and their benefits and risks. Three months before taking hormones, patients should be advised to undergo a period of psychotherapy. Before surgery is considered, the general guidelines stipulate that patients should live full time in their desired gender role for at least a year to see how they cope with work, family, friends and relationships. "I neither lived properly as a woman," says Claudia, "or had counselling to prepare me for what was coming." In 2004 another of Reid's former patients, the businessman Charles Kane, complained that he had been referred for gender-reassignment surgery after living as a woman for only a month.

Despite being an optimistic person, Claudia is dreading growing old alone. "I'll never have a relationship. Who's going to want me when they could get a real woman?" she says. "I am not a woman, I am a sex change, and men know that." For Claudia to live as a woman with a partner, she believes she would have to reinvent her past life and pretend she grew up as a woman, something she is not prepared to do. "It is not possible to integrate and 'pass' in the same way that it used to be, because of all the raised awareness. People know what to look out for."

Claudia is not bitter about her experiences, but would like an apology from Reid, and some financial compensation to reflect that fact that her sex change ruined her career and personal life. She would also like to help prevent other troubled young men going through the same traumatic experiences.

"I fundamentally regret having had surgery. I could have lived as a woman without mutilating my body, but no one talked to me about the possibility," she says. "I could have been enabled to live happily as a gay man. Instead I was put in this box - transsexual - simply because I did not conform to what psychiatrists think a real man should be."

What does Claudia miss about being a man? "Standing up to pee for convenience. Not waiting for the double take when an admirer first clocks me. And I miss having the newly acquired acceptance of my male body. I had just found some when I had the surgery."

As gender-reassignment surgery becomes more commonplace in the UK, with more than 400 operations carried out each year, and since the recent implementation of the gender recognition bill, which allows those who have had reassignment surgery to change their passports and birth certificates to reflect their new sex, society seems to be becoming more accepting of a person's right to decide to change their gender. For Claudia and others who regret having surgery, this is not good news.

"If we allowed people to be as they wish, whether that is a man being camp and feminine or a woman butch and unadorned," says Claudia, "then the need to chop up healthy bodies to achieve that acceptance would diminish".