Will we upset nature's balance by favouring one sex over another, is sex selection unnatural, and will parents driven by the vision of the perfect designer family find themselves bitterly disappointed by the reality? The GCC is run by Dr Peter Liu, a Hong Kong-born biochemist, and Dr Alan Rose, a chemical pathologist and one of the world's leading experts on kidney stones.

The two doctors use an insemination technique developed in the United States by Dr Ron Ericsson in 1973, in which sperm are separated in a centrifuge using albumen (egg white) and those carrying the desired chromosome are implanted into the woman.

According to Dr Liu, who trained under Dr Ericsson in London, sperm carrying the male Y-chromosome swim faster, reaching the bottom of the test tube quicker than the female X-chromosomes.

He said the success rate for a boy was about 75 to 80 per cent, and around 70 per cent for a girl.

''We then pinpoint the wife's ovulation date and when it is near to the time she is to ovulate she needs to come into the clinic and we run urine sample tests,'' Dr Liu said.

''About 24 to 56 hours' notice is needed for the treatment.

''On the day of the actual treatment the husband produces a semen sample at the clinic, and we then check the quality and sperm count.

''The sperm is separated in a process that takes three to four hours and then the selected sperm is inseminated into the wife.

''That is a simple procedure which takes about five or 10 minutes. The whole treatment takes about half a day.'' He estimates the GCC will be able to perform three treatments a day.

''We don't treat a couple unless they have already had a child. The second criteria they have to meet is they have to want the opposite sex of the existing child,'' he said.

''So if they have a girl then we will only help them to have a boy. If, for instance, they have one boy and one girl already then we will not treat them.

''But say they have four boys and one girl then we will help them have another girl to help them balance their family.'' He stressed ''our main role is to help couples balance their families, not to distort them''.

The treatment costs $28,000, but Dr Rose will first check the suitability of a couple, and parents will have to pay another $800 for that initial consultation.

''We prefer married couples. We only provide treatment after checking marriage certificates and birth certificates of existing children,'' Dr Liu said.

Although sex selection is not foolproof, its success rate is growing and Dr Liu estimates that within 10 or 15 years, it may be almost 100 per cent successful.

Sex selection on medical grounds is already widely practised. There are several genetic conditions such as haemophilia, Duchenne's muscular dystrophy and colour blindness which can be prevented by determining the sex of a foetus.

This is usually done with amniocentesis, where sex can be determined in about 15 weeks, or chorionic villus sampling by selectively aborting those whose cells containing the male Y-chromosome.

The same technique can obviously be used for sex selection on social grounds. This is reputedly prevalent in Asia, where Chinese, Muslim and Indian cultures prefer male children.

In India daughters are seen as a financial liability because of the dowry system and one of the greatest compliments that can be paid to an Indian woman is still: ''May you be the mother of a hundred sons.'' A recent study in six Bombay hospitals found that of 8,000 abortions following amniocentesis, all but one were of female foetuses.

China's ''one child'' policy has also created a preference among mainland parents for sons.

This is the doctors' second clinic. Their first GCC opened in London in January, and Drs Liu and Rose have seen almost 500 couples and performed more than 200 treatments so far.

''We had an overwhelming response in London. After we opened, the telephone didn't stop ringing for two or three weeks and then we also had lots of letters from prospective parents wanting to find out more about the clinic,'' Dr Liu said.

''We're hoping to have a similar response here.'' Although the equipment involved in sperm separation costs little, there is a lot of money to be made. Dr Ericsson reportedly sells his technique.

There are already more than 60 clinics in the US, the Middle East and now Hong Kong, using the method which has reportedly made Dr Ericsson a multi-millionaire.

Dr Ericsson defended his technique in British newspapers earlier this year: ''I don't think it is controversial. I am getting irritated. This has been going on for 20 years in the US. You can't ignore what's going on in the rest of the world.'' But the opening of the London Gender Choice Centre created an uproar. The British Medical Association (BMA) declared itself ''dead set against it'', and said sex selection was ''unethical''.

The British Government's statutory body which licenses test tube baby clinics, caught by surprise by the clinic's opening, sprang into action.

The Human Fertilisation and Embryology Authority (HFEA) sent out consultative documents to doctors, parents, organisations and the public asking for their comments.

The overwhelming response from the public was that sex selection should be allowed for medical reasons but not where the reasons were purely social.

Following this the HFEA banned all 107 test tube baby clinics in Britain from providing treatment which would allow parents to choose the sex of their baby unless there was a risk the child would be born with an inherited disease.

But Professor Colin Campbell, head of the authority, did not recommend a total legal ban because, he said, ''we think it is possible public opinion may develop or change over the years''.

The ban ironically does not include the London GCC: it used a method that does not involve test tube baby techniques, and therefore is outside the authority's jurisdiction.

Dr Liu is expecting a similar response in Hong Kong.

''I expect some will oppose what we are doing. Remember how people were opposed to the introduction of contraception and then to test tube babies?'' he said.

''There were so many against it and now it's widely accepted. I think it will take a lot of education and that takes time.'' But if the reaction of the territory's top doctors and academics is anything to go by, that acceptance may not be forthcoming.

Pro-life groups, legislators, doctors and women's organisations have called on the Government to look into the whole question of sex selection.

Dr Liu defends the clinic against its critics.

''We are doing unnatural things all the time. Having a fluorescent light on is unnatural, taking antibiotics is unnatural.

''After we physically separate the male and female sperm, we inseminate the wife and then leave nature to take its course.

''This is not genetic engineering, we are selecting what is already there, not introducing new genetic content.

''Our purpose is to balance families and help reduce family size, it should also help couples financially and, dare I say so, help the state and everyone have stable families.

''I think this is a progression of life.''