British scientists say they have created human-animal "hybrid" embryos which could be used to develop new stem-cell treatments.
They say the hybrid embryos will be used purely for research and would never be allowed to develop beyond 14 days when they are still smaller than a pinhead.
This is first for British science and the team from Newcastle University say they hope the research will lead to new stem-cell treatments for disorders such as Parkinson's disease, stroke and diabetes.
The hybrid embryos were created by merging human genetic material with cow egg cells which had most of their own genetic material removed and the result produced hybrid embryos which were genetically 99.9 per cent human and 0.1 per cent cow.
While the research is still very much at a preliminary stage and has not yet been verified in a peer-reviewed scientific journal, the scientists say the results were valid, and the hybrid embryos survived for a three day period in the test tube.
The researchers hope that eventually such embryos will survive for up to six days - this would allow time for embryonic stem cells to be taken and grown into mature tissue.
Lead researcher Professor John Burn says the research was licensed in January and some progress has already been made and the research is entirely ethical.
The scientists believe that the work is essential despite critics labeling it as monstrous and immoral; medical bodies and patient groups say such research is vital to achieve a better understanding of disease.
The Newcastle team were issued with a research licence from the Human Fertilisation and Embryology Authority with approval from the Government and the British government is proposing to update current legislation to specifically permit such research.
Experts say the approach is likely to provide stem cells for research without the use of human eggs or normal human embryos and the new legislation will confirm the arrangements for regulation in this area of research.