British scientists have been given permission to perform therapeutic cloning using human embryos for the first time.
Stem cells would be used to treat diabetic patients
The Human Fertilisation and Embryology Authority granted the licence to experts at the University of Newcastle.
They are investigating new treatments for conditions including diabetes, Parkinson's and Alzheimer's disease.
The controversial decision could open a new era of research by scientists looking for remedies for diseases.
The research will take place at the International Centre for Life in Newcastle, involving experts from the Institute of Human Genetics at Newcastle University, and the Newcastle Fertility Centre.
Scientists there believe this is the first time such a licence has been granted in any European country.
They warn it will be at least five years - if not many more - before patients could receive stem cell treatments based on their work.
But the ProLife Party has said it is considering mounting a legal challenge against the HFEA's decision to allow the research to go ahead.
Therapeutic cloning has been legal in Britain since 2001.
It is carried out for medical reasons. Even though the science is similar, the technique is different to reproductive cloning, which aims to create a human being.
The cloning technique, known as cell nuclear replacement (CNR) involves removing the nucleus of a human egg cell and replacing it with the nucleus from a human body cell, such as a skin cell.
The egg is then artificially stimulated. This causes the egg to divide and behave in a similar way to a standard embryo fertilised by sperm.
The eggs used are left over from IVF treatment. They are donated by couples, and would otherwise have been destroyed.
Professor Alison Murdoch of the Newcastle NHS Fertility Centre, who is leading the research said the potential of their research was "immensely exciting".
She added: "Since we submitted our application we have had overwhelming support from senior scientists and clinicians from all over the world and many letters from patients who may benefit from the research.
"This research should give valuable insight into the development of many diseases."
But Professor Murdoch said: "Realistically, we have at least five years of further laboratory-based work to do before we move to clinical trials but this could be reduced if we receive additional funding which would allow us to increase the size of our team."
Suzi Leather, chair of the Human Fertilisation and Embryology Authority, said an initial one year research licence had been granted after "careful consideration of all the scientific, ethical, legal and medical aspects of the project".
She said: "This is an important area of research and a responsible use of technology.
"The HFEA is there to make sure any research involving human embryos is scrutinised and properly regulated."
A spokeswoman for the British Medical Association said: "We support strong regulation so that therapeutic cloning to extract embryonic stem cells for life-saving treatment, which most of the public supports, can go ahead while human reproductive cloning, which most of the public opposes, cannot."
But Julia Millington of the ProLife Party, said it planned to take advice over whether it could mount a legal challenge to the HFEA decision.
She said: "It is perverse that, in the current climate of concern for the protection of animals, the HFEA is allowing experimentation on human beings without even a murmur of public opposition."
Professor Jack Scarisbrick of the pro-life charity Life, called the HFEA's decision "deplorable".
"We are all in favour of conquering terrible diseases. But we do not need cloning to do so. Stem cells taken from adults are likely to be just as good, if not better."
Josephine Quintavalle, of the pro-life group Comment On Reproductive Ethics, told the BBC: "It is very worrying indeed. "We have decisions of this magnitude being taken by an unelected government quango."
She added: "No human life should be sacrificed for the benefit of anybody else, no matter how dramatic the promises are.
Cloning human embryos for therapeutic purposes was made legal by an amendment to the Human Embryology Act in January 2001.
But cloning humans for reproductive purposes remains illegal and is punishable by a 10-year prison sentence and unlimited fines.