Indeed, he says that public attitudes in Ulster to those seeking a sex change remain so hostile that many of those able to afford it will avoid the NHS and travel to the Far East for surgery to try and have it done discreetly.

"There is a common misconception that people who want to change sex are sexual deviants. That's simply not the case. The condition is also very distinct from transvestitism, which it is often wrongly confused with," asserts Dr Ingram.

"It's not a disorder of sexuality or sex. Sex is to do with the body. It's a disorder where there is a dissonance between the gender a person feels and the sex of their body.

"We are talking about a very small group of people who have often suffered dreadfully, and probably more so in Northern Ireland because our culture makes it even more difficult for them to come forward than, say, in London or a large city in England.

"Here, there is little chance of anonymity so people tend to be much older by the time they seek help. That means they often have other complications - many have married and have children which creates other issues.

"And it must be such a terribly difficult situation to find yourself in, where you know you are one particular gender, but the sex of your body does not respond to that. It leads to difficulties in relationships, in being intimate with people, and in all that is important for emotional health.

"In fact it often leads to depression, suicide or self-harm - where a person not just wants to be the other sex but cannot look at their own body without feeling an intense hatred of it.

"Often they seek a solution by trying to act the role of the gender that corresponds with their sex but that leads to intense inner conflict until they can no longer live like that."

On average Dr Ingram's patients split 50:50 into men who want to become women and women who wish to become men. In medical terms such people are classified as transsexuals, though many patients balk at the description. They prefer the term 'trans people', or for a female-to-male, 'trans man,' and for a male-to-female, 'trans woman.' "We try to be sensitive over nomenclature. These people often feel marginalised and misunderstood enough without us adding to it," says Dr Ingram.

"For example, we are known as the Gender Identity Clinic but those coming here would say they've no problem at all with knowing what gender they are - it is the sex of their body that is the difficulty."

Occasionally patients concerned they may need a sex change discover they have, in fact, some other condition.

But the vast majority are only too well aware of their predicament and will already have done a great deal of research into it.

Usually patients, who have often waited years before seeking help, are anxious for surgery as quickly as possible.

Yet the operations are so radical they must be regarded as a 'no way back' option, so patients must go through an assessment period, lasting between a year and 18 months.

"First they enter into the 'real life' experience of the sex they wish to become. They change their name by deed poll, all their documentation, how they dress and how they conduct themselves with family and friends," says Dr Ingram.

"We look at how well they adjust - their emotional state, social functioning, how they get on at work."

"Of course, it can be a great shock for a patient's family but I'm often surprised at how well many adapt. Children are offered counselling and they often accept it much better than one would expect.

"Parents and other relatives can take the news quite well, too.

"Many have been aware of some sort of problem for a long time so finding out there is a name for it and that something can be done can be a relief. Who wants to see a relative suffering?"

The next stage is for patients to begin hormone therapy. They will be warned it carries health risks. Oestrogen, given to male-to-females, can cause liver damage, blood clots and high blood pressure. Testosterone, necessary for females-to-males, can also cause liver damage plus increased risk of heart disease.

"Very rarely, when hormone therapy begins there are cases of spontaneous changing in gender. For example a man becoming a woman and given oestrogen suddenly finds his masculine side reasserting itself so strongly in reaction to this that the sex change process ceases," explains Dr Ingram.

Some patients stop short of genital surgery, finding the 'real-life experience' along with hormone therapy has provided sufficient readjustment to feel comfortable.

But most board the plane for London, where such operations are carried out. On average surgery takes four hours and, says Dr Ingram, is "fairly expensive, like any major operation."

Male-to-female gential surgery is now highly successful. "A nurse who checks our patients reports that it is very convincing," says Dr Ingram.

And most don't stop there - going on to have breast augmentation, larynx surgery and electrolysis for hair removal.

For females-to-males there are increasing options. "Many have a mastectomy," says Dr Ingram. "They may also have a phalloplasty, where a pseudo-penis is fashioned. It will never function fully though certain techniques can be used during sex."

Dr Ingram (40), a quietly-spoken Belfastman, never planned a career in gender identity which makes up half his workload. But now he finds it absorbing. He has "never encountered any antipathy to what I do." He says: "The reaction of friends to my job tends to be one of intense interest."

He is convinced the roots of public animosity to trans people lie in our own fears about our sense of gender.

"Freud said 'it is important to understand clearly that the concepts of 'masculine' and 'feminine', whose meanings seem so unambiguous to ordinary people, are amongst the most confused that occur in science,'" he says.

"Transsexualism is a frightening area that strikes at something in all of us."

But Dr Ingram adds forcefully: "It is a well-established, well-understood condition. Most trans people just want to lead an ordinary life and fade back into the background. Six months after surgery they usually leave our clinic and do exactly that.

"And I think anyone aware of the level of suffering this condition causes would be sympathetic towards those affected and would wish whatever could be done to help it, would be done."

How does someone end up in the wrong body?

Dr Ingram cites one post mortem study that found a certain area of the brain in male to female trans people showed similar characteristics as those in a normal woman.

"That would seem to show there is some sort of biological predetermination, though it is a very small piece of evidence," he cautions. "There are also lots of psychological theories linking it to a person's development in early life.

"But the likely truth of the matter is that it is a combination of the two factors."