"Should we screen embryos to eliminate those with genes causing a predisposition to curable cancers, or cancers where the victims live into their thirties or longer? Notwithstanding parents' anguish at knowing their child may die, are such lives not as valuable as any other?

"The Hammersmith hospital team has acknowledged that if it were diagnosing a predisposition to cancer in foetuses in the womb and then carrying out abortions, rather than diagnosing a cancer risk before implanting an embryo into its mother's womb, most people would object. I would agree: it is not ethically acceptable to contemplate abortion for predisposition to such cancers.

"A key problem is the lack of a clear line between 'serious' medical conditions, less serious conditions and non-medical characteristics. There is only a science that is constantly redefining human variation as pathological. We are already, for example, seeing doctors prescribing human growth hormone to short children with no hormone deficiency, in order to make them more socially acceptable.

"What particularly concerns me is the argument that because no abortion need take place, and it is "merely" a matter of finding a normal embryo to implant, the ethical problems are somehow less severe. But the fact that no foetus is being aborted makes no difference at all to the moral and social issue of which medical conditions should be tested for.

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"An even more dangerous aspect is the number of embryos there are to choose from. With prenatal diagnosis we can only weed out the 'worst' foetuses, whereas with 10 embryos to choose from, it will become irresistible to pick and choose the 'best'. If pre-implantation diagnosis becomes widespread, it seems bound to lead to a kind of popular eugenics. All that will be needed is people's natural desire to give their baby the best start in life.

"The commonplace response to this is that pre-implantation diagnosis is far too invasive to become commonplace, But the technical advances that may make IVF more user friendly are already happening and research in the field is receiving massive funding. If the IVF problem is solved, then in 10 years pre-implantation diagnosis may be the technique of choice for the conscientious couple.

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"What makes Lord Winston's latest project particularly instructive is that it illustrates all the elements of the current situation in human genetics. We have doctors wanting to do good, a science moving so fast that even the experts can't keep up, a poorly informed public, a lack of ethical institutions that take the public interest into account and a government that doesn't care. It all adds up to a runaway train without a brake."

David King is editor of GenEthics News.