SCIENTISTS were yesterday given the go-ahead to create human-animal embryos for research into serious and debilitating diseases.

The Human Fertilisation and Embryology Authority (HFEA) said it agreed in principle that British scientists should be able to create the hybrid embryos. But the regulator said each application to use the controversial technology would be scrutinised individually.

The decision paves the way for groundbreaking research in the UK to tackle conditions such as Alzheimer’s, Parkinson’s and motor neurone disease.

Several teams of scientists, including one led by Professor Ian Wilmut in Edinburgh, are expected to apply for permission to use hybrid embryos to create stem cells for their research.

But a pro-life group has condemned such work, saying it is a slippery slope to more extensive work combining human and animal DNA.

Scientists hope to create the hybrid embryos, also known as cytoplasmic embryos, by merging human cells with animal eggs. The result would be an embryo more than 99 per cent human and just 0.1 per cent animal. It would not be allowed to develop for more than a few days.

The embryos are made using eggs from rabbits or cows, whose genetic material is replaced with that of humans. Scientists say it will provide a plentiful supply of embryos from which to extract stem cells. A shortage of human eggs has held up such work.

The government’s Human Tissue and Embryos Bill in May said it would allow the creation of hybrid embryos after initially rejecting the idea. Now, after a lengthy consultation, the HFEA has said such research should be allowed, with controls.

“Having looked at the evidence, the authority has decided that there is no fundamental reason to prevent cytoplasmic hybrid research,” the HFEA said. “However, public opinion is very finely divided, with people generally opposed to this research unless it is tightly regulated and it is likely to lead to scientific or medical advancements.

“This is not a total green light for cytoplasmic hybrid research, but recognition that this area of research can, with caution and careful scrutiny, be permitted.”

The move was welcomed by scientists. Prof Wilmut, director of the Scottish Centre for Regenerative Medicine and head of the team that cloned Dolly the Sheep, said the decision would allow scientists to produce many more stem cells for their work.

“We are currently restricted as to the number of new lines we can make because of a scarcity of human eggs,” he said. “Being able to use rabbit eggs, for example, we can now consider producing valuable new lines, which will model human diseases and lead us to understand how we could treat these in the future.”

Dr Tony Calland, of the British Medical Association, said the research could lead to major medical breakthroughs. “We understand people’s initial resistance to the idea of hybrid embryos, but there would be very strict controls,” he said. But Anthony Ozimic, of the Society for the Protection of Unborn Children, “deplored” the decision. He said that there were “grave ethical and moral objections” to the research.

What is a hybrid animal-human embryo?

Scientists take DNA from human cells and place them in animal eggs which have had most of their genetic material removed. Embryos grown from the eggs are more than 99 per cent human, with only a tiny animal component. Once the embryos have been grown in the lab – for no longer than 14 days – scientists can harvest stem cells for research.

Why do we need to use animal eggs anyway?

Ideally, scientists would collect stem cells from human eggs, but there is a severe shortage of such eggs, holding up research with the potential to help millions with serious diseases. Hybrid research allows scientists to use eggs from animals such as rabbits and cows, which are in plentiful supply.

Why will such research be useful?

Stem cells harvested from the hybrid embryos are a valuable resource as they are the body’s master cells, with the ability to develop into different tissue types.

Which conditions could be helped through hybrid embryo research?

Stem-cell research could be helpful in finding treatments for a wide range of conditions, including serious illnesses such as Alzheimer’s, Parkinson’s, multiple sclerosis and motor neurone disease.

Who is hoping to carry out research with hybrid embryos?

Two teams of British scientists, from London and Newcastle, have already sought permission to create animal-human hybrids for research. These applications will now be considered by the HFEA. Professor Ian Wilmut, of Edinburgh University, had also been preparing his application for hybrid research.

Why is hybrid research so controversial?

Some campaigners have questioned whether it is ethical to mix human and animal material. Pro-life campaigners have opposed stem-cell research because the embryos are destroyed when the cells are harvested.