After being given a licence to start a research programme in January this year, researchers at Newcastle University have now succeeded in transferring a human nucleus, originating from skin cells, into cows' eggs.

The hybrid embryo survived for three days, and scientists are now hopeful the research will pave the way for developing cures for conditions such as blindness, Parkinson's disease, and strokes.

Professor John Burn, head of the Institute of Human Genetics at Newcastle University, said scientists used animal eggs because those from humans were in short supply.

He added: "What we are now hoping that these cells can divide for several days, until we are at the stage where we get a cluster the size of a pin-head and can begin to form an embryo proper.

"If we can get to that stage we can start thinking about, for example, rare diseases, taking an embryo from a person with that disease and this will allow an understanding of disease processes."

The move has proved controversial at a time when church and pro-life groups are trying to gather political support to ban any future research involving hybrid human and animal embryos.

Josephine Quintavalle, of the pro-life group Comment on Reproductive Ethics, said: "I don't think you should create a human life in order to save another one. This research is unethical."