Some men do not feel men enough. Others love men. And some others feel like a woman. And there are women that feel like a man, too. Many of those who have been through sex change operations claim it was the only solution to a stressful condition. But others disagree.

"I should never have had sex change surgery," Claudia MacLean, a transsexual woman told the audience at a recent debate organized by the BBC Radio 4 programme Hecklers and the Royal Society of Medicine in London.

"As a result of the surgery, I am incapable of sex and I have lived a life apart."

Julie Bindel, a leading feminist campaigner and journalist, leads this campaign attempting to persuade medics and trans people that sex change surgery is a harmful mutilation, based on unscientific ideas.

The statement that someone can be "born into the wrong sex" is a deeply threatening concept. Many feminists think that typically masculine or feminine behaviors and feelings are socially determined.

Many in the transsexual lobby say that the tendency to feel masculine or feminine is innate and displaying that gender stereotypical behaviors could be "natural" rather than a social learning. That's why Bindel has a strong political motivation for her skepticism about sex change surgery.

But beyond politics, medical research on transsexualism misses scientific evidence of satisfactory outcomes for patients and there are many stories of post-operative regret.

"I was referred for surgery after a single 45 minute consultation. At no time did I say to that psychiatrist that I felt like a woman. In my opinion what happened to me was all about money." said Claudia.

Another person who expressed publicly regrets about having had sex change surgery is Charles Kane who, as Sam Hashimi, subject of a BBC documentary, showed Sam, a transsexual woman, undergoing a reverse surgery, to be a man again.

"My desire to become a woman had developed following a nervous breakdown," said Charles.

These feelings were induced by a longing to retreat into a fantasy character, not by a real crisis of gender identity.

"When I was in the psychiatric hospital there was a man on one side of me who thought he was King George and another guy on the other side who thought he was Jesus Christ. I decided I was Sam."

Other trans people, like Miranda Ponsonby, say the lack of willingness from society to accept transsexual people can make the surgery rather ineffective. She felt like a woman in a man's body from a young age but following surgery, she has lived a life apart. The results are not the expected ones and she prefers not to have done it.

Of course, there are also stories of overwhelming satisfaction, not just of disappointment and regret. But there isn't any scientific research to asses the overall level of satisfaction following such surgery.

A review made at the School of Health and Related Research at Sheffield University points the poor quality of research in this domain and "little robust evidence exists" on the outcomes for sex change surgery patients.

"The problem is that we tend to lose touch with our patients after a relatively short period of time following surgery." said Dr Kevan Wylie, head of the British body looking into standards of care for sex change surgery patients.

Some local health authorities do not fund sex change operations due to the lack of evidence about the surgical efficacy and psychological benefits of the procedure.