The Human Fertilisation and Embryology Bill allows the creation of animal-human hybrids for medical research. A leading neuroscientist argues why it must become law

I have vivid memories of the announcement of the first human heart transplantation in December 1967. After an almost unseemly race among doctors to be the first to attempt a transplant, it was carried out by the South African surgeon, Christiaan Barnard. His background research - the justification for undertaking such a dangerous procedure - was thin and discouraging, to say the least. And his preparation for the operation was almost devoid of an ethical or legal framework. When it came to the decision to proceed, Barnard said, "I didn't even inform the hospital authorities that I was going to do the operation."

How different medical research is today, with its strict legislation, systems of accreditation and licensing, the ethics and governance committees and regulatory agencies. That contemporary concern with regulation is behind the new Human Fertilisation and Embryology (HFE) Bill. In the light of advances in scientific knowledge, the bill seeks to update Britain's legal framework for this area of medical research which came on to the statute book in 1990. There is a need to maintain openness and strict control in an area of research that raises sensitivities and which could, without a proper code of practice, be abused.

The part of the HFE Bill that has provoked most concern from some (but not all) religious leaders covers the combination of human and animal material. Among the much-reported comments from church leaders were claims that such research is of "Frankenstein proportion", touching "on the sacredness of human life, its meaning and purpose" and (from an Anglican bishop) playing "games with ... humanity".

The image conjured up by some comments is of fully formed, half-human, half-animal monsters. Yet a major feature of the bill is that it forbids any attempt to make such things. A key technique acknowledged in the bill, already permitted under existing law, is the formation of "cytoplasmic hybrids", involving the insertion of the nucleus of a single human cell (for instance from a patient suffering from a genetic disease) into the empty egg of, say, a rabbit. The resulting cell, although it does not result from fertilisation and its genetic material is almost entirely derived from the adult donor, has the characteristics of an embryo. It divides and, most significantly, stem cells can be collected from it for research. The bill would prevent such "human admixed embryos" from being maintained for more than 14 days (the Warnock limit, embodied in the 1990 Act), when they would be a tiny ball of a few hundred cells no bigger than a pinpoint. And they could not, of course, be implanted.

One of the advantages (and I would argue that this is a moral as well as a practical advantage) is that this technique allows the production of stem cells for research without the use of human eggs or normal human embryos. The study of stem cells that are known to carry disease genes is likely to give valuable insight into the basis of these terrible diseases, and may be useful in the production and testing of potential new treatments.

Some critics imply that research on adult stem cells (for instance from bone marrow) could substitute for all the use of embryonic stem cells. My research colleagues strongly deny this, but do see the possibility that knowledge from stem-cell research might increase the potential for therapeutic use of adult stem cells. Some point to the recent development of methods to transform ordinary adult cells into cells with the characteristics of embryonic stem cells. But these techniques involve viral infection and genetic modification, which makes many nervous about the utility of such cells. However, research on embryonic stem cells will undoubtedly help us to do more with adult cells.

Transgenic mice that carry human genes are another form of human-animal combination covered by the bill. Such animals, carrying genes that produce such conditions as Huntington's disease and Down's syndrome, are already playing a vital role in research. I don't think that most people would see such strains of mice, whose cells carry a fragment of human DNA, as offensive monsters.

Last Monday, I wrote a letter to The Times suggesting that a discussion between religious leaders, concerned MPs and representatives of the scientific community could provide a way forward. I do not think that scientists should challenge the spiritual leadership of the clergy, but they can provide authoritative information that should play a part in underpinning ethical judgements. Jim Devine, a Catholic Labour MP, independently made a similar proposal. I am delighted to report that several leading scientists have already volunteered and officials from the Catholic Bishops' Conference of England and Wales have offered to organise such discussions.

What should not be forgotten is that many people see a strong moral argument for this area of science, and the dedication of the many British stem-cell researchers that I know is beyond question. There can be no guarantees, but stem-cell research does offer a radical new approach to the understanding of dreadful, currently incurable diseases, such as diabetes, Parkinson's, and motor neuron disease. And it could lead to new treatments as revolutionary as heart transplantation was in 1967. This is why the Association of Medical Research Charities and the Genetic Interest Group, representing more than 220 medical charities and patient groups, has recently written to all MPs asking them to support the bill.

I suspect that some people who were shocked by the first announcement of Barnard's work are among the 4,000 who are now saved every year by heart transplantation, 95 per cent of whom now live at least five years. I would ask those religious leaders who are currently nervous about the HFE Bill to consider whether they would instruct their congregations to refuse new treatments for horrific diseases that flow from the kind of research that it will regulate.