I can see the headlines now: “Scientists grow human with rabbit ears”. This is a reference to the human-animal eggs and embryos that researchers in Britain propose to create for research into stem cell therapy, opening up the possibility of treating a range of degenerative diseases such as Parkinson’s, Alzheimer’s, motor neurone disease and muscular atrophies that affect millions worldwide and for which existing treatments are of limited effect.

With so much at stake, we need to look beyond caricature to the science. The government recently proposed a ban on creating human-animal embryos. So it is important that there is a sophisticated dialogue between the regulators, the politicians, the scientists and the public. We need to understand what worries you and anticipate your questions. We have to battle not only against these terrible diseases but also against misunderstanding and fear.

It is easy to create alarmist headlines. That is why I welcome last week’s decision by the Human Fertilisation and Embryology Authority (HFEA) not to rule against this kind of work but to hold a scientific and public consultation. If we can explain what the human-animal embryo really is and how limited its life will be, as well as the benefits to humanity from these experiments, we will be giving people the material they need to come to an informed opinion about the ethics involved.

We have a deep-seated cultural anxiety about hybrids, so ancient that it is echoed in our mythologies — as in the stories of the Minotaur or the centaurs that are depicted around the Parthenon. Such creatures appear unnatural and make us feel uncomfortable. We should remember that there are some naturally occurring hybrids, too: the horse and donkey combine to make a mule, for example. But when humans are involved we feel more uncomfortable.

Understanding more precisely what the human-animal embryo actually is, and how it can be used, will help us to accept this work as a positive development.

Embryonic stems cells are derived from the early embryos of any mammal. They have the potential to change into any of the different cells in the body, for example, brain, muscle or liver cells. When introduced into damaged human tissues and organs, they may be able to reverse the effects of degenerative diseases such as Parkinson’s.

The proposed work on human-animal eggs is crucial for research. Human eggs are rare and hard to work with, making progress slow and difficult. By contrast, eggs from animals such as rabbits or cows are plentiful and of good quality. The idea is to take a rabbit egg, for example, remove all the rabbit genes (its genome) and replace these with a human nucleus or cell containing the human genome. As the egg repeatedly divides to form the mass of cells that make up an early embryo, the components of the rabbit egg are replaced by human components.

The stem cells derived from such embryos will be almost 100% human. These will be used solely for research; they will never be used in patients, and human-animal eggs will never be allowed to grow into a developed hybrid animal. But they will allow researchers to improve embryonic stem cell production and to study what goes wrong in the development of the muscle or nerve cells of patients with degenerative diseases.

Two groups of scientists in Britain, initially, want to carry out these procedures and they have my full backing. Together with countries such as Sweden, South Korea, China and Israel, the UK is at the forefront of gene therapy and the HFEA is a highly respected body that has built a reputation for allowing first-class research. As the former head of Cancer Research UK, I know from experience that our ability to attract the best scientists in the world to our centres of excellence will be in jeopardy if we cannot carry out such experiments. So there is a huge responsibility for us in Britain to get this ruling right. The world respects the way we regulate science in the UK and looks to us to take the lead.

Scientists can only do what governments allow. Last week, for the second time in seven months, Congress in the United States, where I now work, voted in favour of relaxing the rules governing embryo research. It did so last July but the legislation was vetoed by President Bush; we are now waiting to see whether he will change his position in response to the new vote.

The present constraints in the United States mean that at the Rockefeller University in New York, of which I am now the president, the scientists cannot create new human embryonic cell lines using federal money. We have to use private support for this research, and we need to employ highly bureaucratic measures to keep the work completely separate from research in the university supported by federal funds.

The Commons science and technology committee has concluded that the proposed procedures using human-animal eggs are ethically acceptable. As well as the public good, there are commercial ramifications for Britain in developing effective therapies for degenerative diseases.

The benefits to be derived from allowing this work are numerous. The scientific community needs to speak out in support of it, offering as much information as it can. I ask you to understand the significance of this crucial work, so that we may all move in the direction of finding better treatments, or even cures, for some of the terrible diseases that millions endure.

Sir Paul Nurse is a scientist who won a Nobel prize for research on cell division