Once, if you felt you were born the wrong gender in the wrong body, you had to put up with it. Now, there are up to 400 sex change operations a year carried out in Britain. Some transsexuals who resort to surgery live to regret it, others decidedly do not. David Batty hears their stories

Two months ago, Marissa Dainton changed sex for the third time in 11 years. She started life as Mark Dainton in 1967. In 1992, a year before her first sex change operation, she took the name Patricia Vincent. Four years later, Patricia decided to go back to living as Mark. Now she has become a woman again. Sitting in the lounge of the small terrace house she shares with her wife, her eyes stray to the wedding photo on the mantelpiece. "What happened to me should be a lesson in the need to make sure you're really ready before changing gender," she says.

Once Dainton had a penis, then a vagina, now she has nothing. Soon after her first sex change, she joined an evangelical church and became convinced her operation was sinful. She stopped taking oestrogen and was prescribed testosterone. Her beard and body hair began to grow back, and her sex drive soared. Before getting married to another member of the congregation six years ago, she had her artificial vagina removed. This left her with smooth skin where her genitals once were.

"My wife said she'd feel more comfortable about having a physical relationship if I didn't have a vagina. You'd have thought I'd have realised it was a mistake because I wasn't bothered about not being a 'complete man'. I never missed what was taken away," she says, smiling sardonically.

Her sex change reversal was hailed as a miracle by her church. "I became their cause célèbre." In secret she was still cross-dressing, although it wasn't until last year that she decided she wanted to become a woman again. "My biggest fear was spending the rest of my life shuttling between genders. But I realised I was heading for a breakdown and couldn't go on denying my true feelings. I had to become a woman again."

She went back on oestrogen and had electrolysis to remove her male hair growth. This time the only surgery she had was breast implants. Without genitals, the only way to create a new vagina would be to remove a section of her bowel, which could leave her needing a colostomy bag. "I can only possibly envisage putting myself through what is very painful and risky surgery if I had a new partner and we decided it would help our relationship sexually," she says.

Yet Dainton, 36, considers herself lucky. She works as a senior nurse in a local NHS hospital. She feels accepted as a woman and attracts no unwelcome attention walking through her home town of Eastbourne in a skirt, top and make-up.

Nevertheless, she feels she might have been spared her gender identity crisis had doctors better prepared her for her first sex change. "There was a lot of emphasis on deportment, ways of speaking and behaviour," she recalls, "some talk of what you could expect sexually with the results of the surgery, but in terms of addressing getting on with life afterwards, there was very little."

Around 5,000 people in Britain have had a sex change, with up to 400 operations performed each year. Public acceptance of transsexuals has grown in recent years. (In this year's Big Brother, transsexual Nadia is among the favourites.) The Gender Recognition Act, which gained royal assent earlier this month, will allow them to gain the legal status of their acquired gender, change their birth certificates and marry.

Paradoxically, a growing number of post-operative transsexuals are scathing about their medical care. International research suggests that 3-18% of them come to regret switching gender. The issue has gained public attention since January when the General Medical Council (GMC) began an inquiry into the UK's best-known expert on transsexualism, consultant psychiatrist Russell Reid. Last month the GMC announced that Dr Reid will face a charge of serious professional misconduct over allegations that he has put his patients' health at risk.

The controversy has led some medics and transsexuals to question whether it is appropriate for people confused about their gender identity to undergo an irreversible operation. I have spoken to several of those who now regret the surgery to try to find out what is going wrong, and how they cope with living in the wrong body. Some are attempting to go back to living in their original gender role. Others feel trapped in "gender limbo".

Claudia, 46, says there is "an obituary element" to her decision to speak out. "I feel I've taken this life as far as I can. I'm not saying I'm going to kill myself tomorrow but I don't know what comes next. I can hardly bear it any more." She had genital surgery in 1986. Growing up as a boy in Glasgow, she was bullied because of her androgynous looks. She started dressing as a woman full-time at 18 and found herself being complimented on her appearance. "Suddenly people weren't throwing stones at me," she says. But she believes she should never have been allowed to change sex.

"I changed for all the wrong reasons," Claudia admits. She hoped the surgery would save her troubled relationship with her boyfriend and business partner. "I'm not saying that I was deranged but I was certainly the saddest I'd ever been." Desperate to be referred to a surgeon, renowned in the transsexual community, who was due to retire, she went to see a psychiatrist. "I said, I want this doctor to do my surgery, and therefore the race is on. That should have set alarm bells ringing."

Her boyfriend left her in 1987 - a year after the operation. "It was horrible, I'd created a monster," says Claudia. "One day I was making love and something didn't feel right. There was this little ball of hair like a Brillo pad in my vagina." In 1995 she went to see a surgeon who pulled the hair out but warned it would grow back. "He said it would always be there because I hadn't had electrolysis on my scrotum before the sex change made it part of my vagina. When I heard that, I just sat and cried."

Access to surgery is controlled by transgender psychiatrists specialising in the treatment of gender identity disorders (GID). Their role is to check that patients are truly transsexual and possess an overwhelming desire to become the gender they feel they always should have been. The psychiatrists must rule out mental illnesses, such as schizophrenia or manic depression, as the cause of the patient's desire to switch gender, and ensure they are not a transvestite who just enjoys cross-dressing.

This is not an easy task. Many transsexuals suffer from serious mental health problems as a result of the prejudice they face and the torment of living in what they regard as the wrong body. It can be particularly difficult to judge whether patients with borderline personality disorder, characterised by impulsive behaviour, a poor sense of identity and self-harm, are genuinely transsexual. Transgender psychiatrists admit that the boundaries between transsexualism, transvestism and homosexuality are still not entirely clear to them, so a thorough exploration of the patient's history and lifestyle is essential.

Claudia believes her assessment was superficial. She says her psychiatrist was interested only in whether she looked like a born woman. "I was referred for surgery after one 45-minute appointment. The emphasis was on one thing - my appearance. My motives for wanting the operation were never explored. The psychiatrist asked the most general questions. Did I play with dolls, did I have a strong male role model. There was no interest in the life I lived or how I made a living. Now I'm living on my own in a council flat. This is the last place I ever wanted to be."

Dr Brian Ferguson, a transgender psychiatrist in Nottingham, says that patients are not referred for surgery on the basis of their looks alone. "There's a notion that if they don't wear pearls and a skirt, we'll send them away, but that isn't the case," he says. "We wouldn't want to judge someone on their appearance. You see some male-to-female transsexuals who manage to live very well in role despite some very masculine features."

But the transgender pressure group Press For Change, which campaigns for equal rights for transsexuals, believes that psychiatrists have stereotypical ideas about masculinity and femininity. One of its lead campaigners, Christine Burns, claims some psychiatrists refer for surgery only those patients whom they consider attractive. "The likely success - or otherwise - of a patient is often judged on their physical reaction to a client. They think, that's a good-looking woman, she'll do well in society."

Before her sex change, Claudia enjoyed success as a singer, performing at the Hippodrome and supporting Marc Almond. With her billowing brunette tresses streaked with grey, she still conveys the glamour of her old publicity shots. But she has lost the confidence to face an audience. Passing as a born woman is little help when dealing with prejudice, she says.

"My psychiatrist told me, you look great, you can pass. I've come to realise that human life is made up of connecting, not passing. I can 'pass' in a shop, I can 'pass' on the street. But when you tell a man your background, if you're lucky he'll walk away. Nothing can prepare you for that. I feel notorious in any group. You can say you're Napoleon but unless the whole world agrees with you, you patently are not Napoleon. I'm not a woman, I'm a thing - a chimera. As I move into my middle years, I'm genuinely worried that I just don't fit anywhere."

This sentiment is shared by Paul Rowe, who took the name Paula following genital surgery 15 years ago. Rowe, 54, believes he was wrongly diagnosed as transsexual while suffering from severe depression following a string of personal traumas including the death of his mother. He now considers himself "trapped between male and female", and dresses in baggy trousers and T-shirts to disguise his breasts and hips. "Sometimes I don't know which toilets to go into. I get challenged if I go in the ladies', but if I go in the gents', they stare at my boobs," he says.

Since Rowe stopped wearing women's clothes, he has regularly been harassed at his home in London. Gangs of youths have spat at him and called him names including paedophile and weirdo. He has considered surgery to try to reconstruct his penis but decided the results would be unsatisfactory. He was due to have a mastectomy in March but backed out of that, too. "I can never become a complete man again. There's no turning back."

The surgical options for men who regret changing sex are limited. Urological surgeon James Bellringer says the best a patient could expect is something that vaguely resembles an upside-down penis. The doctor, who has performed more than 200 male-to-female (MTF) sex changes in the past four years, says: "The erectile tissue has been taken out, so you need a prosthetic. The urethra's gone, so you'd have to construct one out of a tube of skin. The tip of the penis will have been made into a neo-clitoris and I don't think you could put it back in its original place. It would probably be at the base of the artificial phallus. It's a mess."

Yet a minority of those who regret changing sex do decide to resume their original identity. For Alan Finch, from Melbourne, Australia, the decision was agonising. Finch, who grew up in West Yorkshire, says: "My mother was terrified. She thought I'd be a freak. She said how could I possibly live like a man without a penis? For a year I felt the same way. Then I realised actually I am a man living without a penis. The only difference now is I don't have to wear stupid high heels and a dress."

Finch, 35, had a nose job to make his face look masculine again. Then a surgeon who treats female-to-male (FTM) transsexuals removed his excess breast tissue. He is considering surgery to remove his artificial vagina for "health and hygiene reasons". "It's made of skin that's meant to be on the outside of the body that's now scuffed and crusty." He will not have an artificial penis constructed because he wants nothing more to do with doctors involved in gender reassignment. "I can't see much point in mutilating my body any more."

Changing sex has always been controversial. The first recorded cases in the early 20th century show doctors were baffled when apparently healthy people requested gender reassignment. Some doctors considered them a type of homosexual, transvestite or hermaphrodite; others labelled them mentally ill, deviants or perverts. Some patients were treated with electric shock therapy, supposedly to relieve their depression. Many doctors preferred to let someone commit suicide rather than offer them treatment.

By the 1960s, patients were travelling across the world for surgery, usually to Casablanca. But during that decade the term transsexual gained greater acceptance among the medical profession, and gender identity clinics, providing hormones and surgery, opened in the US and UK. The first British clinic opened at Charing Cross hospital in west London. Back then, it received about 50 referrals a year. By the mid-1980s, this had risen to 100-200. Now around 1,300 patients are referred annually. Last year the clinic, which is the main NHS centre for the treatment of GID, carried out 100 male to female sex changes and the number is expected to rise to more than 150 by 2005. Of these, only a few are female-to-male transsexuals - 450 out of the total of 5,000 sex changes. Among these, genital surgery is less common - and harder to achieve successfully - and so the change is easier to reverse should it not work out well.

Rachael Padman, a physicist at Cambridge University, was treated at Charing Cross from 1977 to 1982. Now aged 50, she has no regrets about her decision to change gender. Although she had an overwhelming desire to change gender from early childhood, Padman believes the main reason for her post-op success is that her identity is not solely based on her being transsexual. She was working on her doctorate while undergoing gender reassignment. She saw genital surgery as just a step towards leading the life she wanted, rather than her ultimate goal. She says: "I don't think that surgery is what created me. I suppose it did make me feel more female because I wasn't loaded up with two competing sets of hormones any more. But being an astronomer and physicist is my prime identity. I do get the impression that some people lose sight of the rest of their life."

She believes this attitude helped her to overcome the only crisis she has faced since changing sex. In 1996, she was invited to take up a fellowship at Newnham, one of Cambridge's three all-women colleges. Germaine Greer, who was then a fellow of the college, subsequently argued that since Padman was legally a man, her appointment contravened college statutes. After a very public airing of the debate, Padman initially became preoccupied with whether she came across as female. But she says the experience taught her to get on with being herself rather than worrying how others judge her.

Padman, who grew up in Australia, says the support of her friends, family and colleagues is crucial to her happiness. "I'm amazed that people cut themselves off and try to invent a false history for themselves," she says. "I don't know how they cope. Who gives a toss what someone in the street, whom you've never met before, thinks if your friends and family are supportive." But she admits she is lucky to work in a laid-back and liberal environment.

Despite such success stories, primary care trusts remain reluctant to fund gender reassignment. Some health officials dispute its long-term benefits, while others regard it as a lifestyle, rather than a life-saving, treatment. This has led to a black market in transsexual hormones, increasingly accessible via the internet, and growing numbers of people travelling to the far east for surgery.

Guidelines set by the Harry Benjamin International Gender Dysphoria Association, based in Minneapolis, set minimum criteria for gender reassignment to prevent inappropriate sex changes. These standards of care are recognised in most countries. Patients should undergo at least three months of psychotherapy before taking sex-changing hormones. They should then live full-time in their desired gender role for at least a year before surgery, to see how they cope with work, family, friends and relationships. But the guidelines are not legally binding. They are flexible directions, which can be modified to suit a patient's needs. In Dainton's case this meant cutting short the time she spent living as a woman prior to surgery, called the real life experience (RLE). She says, "It suited me fine. I was due to start a nursing course in seven months and it was agreed I'd have the operation before that. But with hindsight it was not a good idea."

Two years ago, Ferguson carried out a survey that revealed wide variations in the treatment of transsexualism across Britain. Some clinics offered "surgery on demand", others no surgery. He believes a two-year RLE is preferable. "The patient is not just starting a new life; they're leaving behind the life they've lived and relationships that have been important to them - even if they've been traumatic relationships. But it can be very difficult to get them to be realistic about the future."

Dr Marguerite Paffard, a psychiatrist who works with Ferguson at the Stonebridge Centre gender clinic, shares his concerns. "We've seen individuals for whom two years' RLE was ideal because they expressed doubts or changed their minds about surgery only after 18-20 months."

Some people choose to conceal their doubts. Many transsexual websites offer tips on what to say in order to meet the criteria for treatment: how to dress, talk and behave. Dainton says patients encourage each other purposely to avoid discussing issues that might hold up their treatment. "Most people who go to psychiatrists with a view to changing gender have actually researched and know a lot of the things they should say - and some of the things they should stay clear of."

When she first changed sex, Dainton chose not to discuss the rejection she felt as a result of being given up for adoption. Nor did she talk about the impact of her adoptive mother's death, which affected her like another parental rejection. "I didn't dwell on it because I thought it might complicate matters and slow things down," she says with a half-smile. "I expected the surgery to solve those anxieties about my identity and when it didn't, I began to wonder whether I'd done the right thing."

The Royal College of Psychiatrists (RCP) has set up a gender identity disorder working party to draw up new UK guidelines to address the concerns of medics and transsexuals. Its chair, Kevan Wylie, a consultant psychiatrist in Sheffield, wants to see patients assessed and supported by a range of counsellors, therapists, psychiatrists or psychologists, rather than just one psychiatrist as is often the case. He believes a team of experts is more likely to spot a patient's misgivings.

The guidance will also set out what continuing care patients should receive. Better after-care would be welcomed by Dainton. "My follow-up care consisted of one or maybe two consultations with the surgeon to check everything was OK physically," she says. "I was offered an appointment with my psychiatrist but it wasn't mandatory. I can't think of another major operation where there's so little aftercare. Had it been available, it might have prevented me getting into the trouble I did."

Dr Wylie says that draft UK standards of care are expected to be ready next January. But this deadline looks increasingly unlikely. The GMC inquiry into Russell Reid has pitted members of the RCP working party against one another in what the college describes as "a dispute between experts". Some of the complaints against Reid were brought by four other doctors who specialise in treating gender identity disorders, one of whom has called on him to resign from the group. Wylie admits: "There is currently no consensus on treatment."

The lack of medical consensus has led some to call for a moratorium on gender reassignment. Alan Finch helped to set up the Gender Identity Awareness Association, to dissuade people from genital surgery and campaign against what he calls the "sex change industry". In April, the chief psychiatrist of Victoria State began an inquiry into the Monash gender clinic, Melbourne, where Finch was treated. But Finch wants all treatment stopped, arguing that transsexualism was invented by psychiatrists.

"Their language is illusory. You fundamentally can't change sex," he says. "The surgery doesn't alter you genetically. It's genital mutilation. My 'vagina' was just the bag of my scrotum. It's like a pouch, like a kangaroo. What's scary is you still feel like you have a penis when you're sexually aroused. It's like phantom limb syndrome. It's all been a terrible misadventure. I've never been a woman, just Alan."

Finch, formerly known as Helen, wants to know why people who want a sex change are treated differently from other psychiatric patients who hate their bodies. He says: "The fact that someone's suicidal and wanting something isn't a reason to provide it. The analogy I use about giving surgery to someone desperate to change sex is it's a bit like offering liposuction to an anorexic."

Does Finch have a point? Ferguson says only hormones and surgery have proved effective in treating transsexualism. "Psychotherapy has not been successful at 'curing' transsexuals in contrast to people with other body identity disorders, such as anorexia or body dysmorphia." Wylie says that all his patients' lives have drastically improved following surgery. But he admits that there is a lack of robust scientific research to support this positive anecdotal evidence.

Guardian Weekend asked Birmingham University's Aggressive Research Intelligence Facility (Arif) to assess the findings of more than 100 follow-up studies of post-operative transsexuals. Arif, which conducts reviews of healthcare treatments for the NHS, concludes that none of the studies provides conclusive evidence that gender reassignment is beneficial for patients. It found that most research was poorly designed, which skewed the results in favour of physically changing sex. There was no evaluation of whether other treatments, such as long-term counselling, might help transsexuals, or whether their gender confusion might lessen over time. Arif says the findings of the few studies that have tracked significant numbers of patients over several years were flawed because the researchers lost track of at least half of the participants. The potential complications of hormones and genital surgery, which include deep vein thrombosis and incontinence respectively, have not been thoroughly investigated, either. "There is huge uncertainty over whether changing someone's sex is a good or a bad thing," says Dr Chris Hyde, director of Arif. "While no doubt great care is taken to ensure that appropriate patients undergo gender reassignment, there's still a large number of people who have the surgery but remain traumatised - often to the point of committing suicide."

Given that each sex change operation costs the NHS at least £3,000, why has there been so little long-term research? Wylie admits more scientific evidence is needed. But he says it would be difficult to carry out: "With transsexualism being such a rare experience, it's very hard to put people through a series of procedures or trials to compare different treatments." Surgeon James Bellringer adds: "I don't think that any research that denied transsexual patients treatment would get past an ethics committee. There's no other treatment that works. You either have an operation or suffer a miserable life. A fifth of those who don't get treatment commit suicide."

Dr Andrew McCulloch, chief executive of the Mental Health Foundation, has asked the mental health minister, Rosie Winterton, to set up an inquiry into gender reassignment. He says: "I find it extraordinary that there's no long-term research into its outcome. It's a very drastic procedure to perform with no scientific evidence. To say you can't do research is a cop-out."

But Wylie says many patients drop out of follow-up studies because, after having genital surgery, they no longer consider themselves transsexual. Dainton says she wanted to "bury" her male identity when she first changed gender. "I remember writing in my diary, hello Patricia - excuse my French - sod off and die Mark," she says. "I wanted to forget I was transsexual. I wanted to maintain the impression that I was completely female. I used to carry tampons around in my handbag, just in case someone saw them or someone wanted to borrow them." Her determination to pass as a born woman led Dainton to cut her ties with other transsexuals. But doing so left her isolated. "Those that pass tend to leave the transsexual scene and pretend that they are a woman and always have been. What they're trying to do is deny to themselves who they really are and what their situation is. I'm sure that made me vulnerable," she says.

She joined a local evangelical church to find a new social circle. At first she was accepted. But in the spring of 1994, while preparing for baptism, she decided to reveal her past to the pastor and his wife. "I wanted to be honest about who I was," she says. "They were taken aback. They saw my surgery as an act of rebellion against God." Although Dainton accepts that the church thought it was acting in her best interests, she says that over the next two years, its teachings undermined her female identity. "I was swallowing the fundamentalist sermons week in, week out. I so wanted to be accepted."

This desire to conform led her to approach the evangelical Parakaleo Ministry, based in Bromley, south London. Keith Tiller, the man behind the ministry, says he was a habitual cross-dresser before letting God into his life. He now seeks to reconcile transsexuals with the bodies they were born with. Dainton contacted Tiller in 1996 and they went on to co-author a booklet called Male And Female He Created Them. Dainton wrote in the pamphlet that she had decided to resume living in her "once hated male identity" after God revealed her sex change to be "born of sin".

When her desire to cross-dress returned only six months after becoming Mark again, Dainton was confused: "I thought, I'm supposed to be healed and yet I'm drawn back to this. The church had made such a big hoo-ha, I didn't feel I had anywhere to go." So she fell into a cycle of accumulating women's clothes, then feeling ashamed. This continued until last year Dainton joined a transsexual website. Going out on the transsexual scene, she realised she had not been misdiagnosed and her desire to resume living as a woman became overwhelming. "I knew that things had gone beyond the point of holding my feelings in any more," she says. This time there were no medical criteria to meet. "Nothing I've done this time is irreversible - I've already lost my genitals."

Her wife was shocked because they had recently looked into adopting a child. Social services were concerned that Dainton would not be a good father as he might change sex again, so ordered him to be assessed by another transgender psychiatrist. The psychiatrist said he could not categorically state that Dainton would stay living as a man. "I thought that was very perceptive of him," she says. "That was one of the triggers to stop pretending to my wife. And I couldn't involve a child in this tissue of lies."

Remarkably, the couple have reached a degree of understanding. "I was all prepared for us to separate but we didn't want to, so we agreed to find another solution," says Dainton. They intend to stay together to try to work out an amicable separation. "It's a very hard situation. As she sees it, she's lost her husband. I find myself in this bizarre situation of trying to comfort her in her grief and I'm the person she's grieving for."

Tiller feels deceived by Dainton and suggests her latest sex change will not be her last. "I have always thought Mark was vulnerable," he says. "Unfortunately I relied on his integrity to tell me, truthfully, if he was struggling. It is now obvious that reliance was not justified." But he remains adamant that his cause is just. "I personally know people in the US and Australia who have resumed living in their original biological gender role. Nearly all claim to have done so as a result of Christian conviction."

For Burns of Press For Change, Dainton's story illustrates how important it is that transsexuals don't lose sight of their roots. "People ask me how I can identify myself as a transwoman. I reply that being transsexual will remain a second-class label unless it's attached to first-rate people! But my real concerns are for the waifs and strays of our community who become detached from the mutual support that transpeople rely on in the absence of professional care. When someone feels shunned by people around them and hasn't anyone else to turn to, they are vulnerable, and Marissa's story illustrates the heartache that is then likely to follow."

After a long struggle with her gender identity, Dainton believes she is now wiser. She says: "It's taken eight years finally to get to grips with myself and the reality of my situation. I know I will never be anything other than a transsexual. As long as I live, I will never be a real woman - no matter how well I pass. Unless you really come to terms with this, the transsexual lifestyle can be unbearably hard. If we throw away our support by burying ourselves in 'normal society', it can also become unbearably lonely. So my message is, proceed with caution."