The government's fertility regulator today agreed in principle that scientists should be allowed to create human-animal embryos for medical research.
As had been widely anticipated, the Human Fertilisation and Embryology Authority (HFEA) agreed to the proposal after the publication this week of public consultation on the controversial research. This data indicated that most Britons were "at ease" with the idea.
The decision means a licence committee may now appraise applications already lodged with the HFEA from scientists at King's College London and Newcastle University to create human-animal embryos. This will probably happen in November.
Dr Lyle Armstrong of Newcastle University's Institute for Human Genetics called the decision "excellent news".
"It is a positive outcome, not just for our work but for the progress of British science in general, and we hope that this will lead to new technologies to benefit everyone," he said.
Scientists hope the creation of what are known as cytoplasmic embryos, the result of merging human cells with animal eggs, could significantly aid medical research.
The plan is to extract valuable embryonic stem cells from the embryos. These could be used to develop revolutionary therapies for diseases such as Alzheimer's and Parkinson's, and even spinal cord injuries.
The HFEA said the decision was not a "green light" for all cytoplasmic research but meant that the licence committee would now be able to appraise each application on its own merits.
Having examined the evidence, the HFEA said in a statement, it had decided there was "no fundamental reason" to prevent the research. "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," it added.
"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."
Such embryos are more than 99% human, with an animal component representing around 0.1%. They are made using eggs from rabbits or cows, and genetic material from human donors.
The embryos must be destroyed after 14 days, when they are still no bigger than a pinhead. They may not be implanted into the womb.
The consultation papers were released on Monday, prior to the HFEA's decision, which marks the end of almost a year of intense lobbying by scientists in favour of the move and organisations opposed to it.
Opponents of the research and some religious groups say the work blurs the distinction between humans and animals, and creates embryos that are destined to be destroyed when stem cells are extracted from them.
Anthony Ozimic, secretary of the anti-abortion group the Society for the Protection of Unborn Children said he "deplored" the decision.
"This is not just a case of the 'yuk factor', he warned. "There are grave ethical and moral objections to this research and the way it is being promoted."
Dr Tony Calland, chairman of the British Medical Association's medical ethics committee, said he could appreciate people's resistance to the idea, but stressed such research would be both carefully regulated and potentially of enormous benefit.
"This kind of research could lead to major breakthroughs in treatments for Alzheimer's, Parkinson's and other serious diseases," he said.