The creator of Dolly the sheep has been granted a licence to clone human embryos for medical research.
The team hopes to produce cloned cells from patients with motor neurone disease
Professor Ian Wilmut and Kings College London scientists will clone early stage embryos to study motor neurone disease (MND).
This is the second time the Human Fertilisation and Embryology Authority has given such permission.
Critics maintain that testing human embryos is immoral. Others question the potential benefits of the work.
Professor Wilmut said it will mean MND can be studied in unprecedented detail.
Therapeutic cloning for research has been legal in the UK since 2001 and it would be only the second time the authority has given consent.
The professor's team was the first to apply for a therapeutic cloning licence in the country.
Up until now, scientists have wanted to create cloned embryos to see if they can be grown into tissues to repair damaged body parts.
But Professor Wilmut's proposal is different as he does not plan to grow healthy replacement tissue.
Instead he aims to deliberately clone embryos that have MND from patients who have the condition.
Professor Wilmut, of the Roslin Institute in Edinburgh, says cells from the embryos can be used to study how the disease progresses in very close detail.
He also said the cells can be used to try out new drugs to see if they stop the disease from progressing.
MND is caused by the death of cells - called motor neurones - that control movement in the brain and spinal cord.
It affects about 5,000 people in the UK. Half of people with MND die within 14 months of diagnosis.
Weakness in the muscles that supply the face and throat also cause problems with speech and difficulty chewing and swallowing.
The aim is to study what goes wrong in the nerve cells of patients suffering from MND.
Patients groups said studying human embryo cells might provide more information than animal experiments alone.
Those opposed to the research said the work is unethical, unnecessary and a step toward full blown human cloning.
However, Professor Wilmut has previously stressed that his team has no intention of producing cloned babies, and said the embryos will be destroyed after experimentation.
He said: "Our aim will be to generate stem cells purely for research purposes."
The MND Association has endorsed the project.
Professor Roger Pederson, professor of regenerative medicine at Cambridge University, said: "This is a very exciting development. It will enable the disease to be studied throughout its development.
"It's very likely to work."
He dismissed concerns that the technology might be used to clone a human being, saying there were strict UK laws that prohibited the transfer of any such embryo to a woman's womb.
But Dr Donald Bruce, from the Church of Scotland's Technology Project, said unless there was a global ban on cloning there was still a threat.
"Science does not know any boundaries."
A spokesperson for Comment on Reproductive Ethics (CORE) said: "Human cloning remains dangerous, undesirable and unnecessary.
"Alternative therapies and research with adult and umbilical cord blood stem cells are already providing safe and ethical solutions in this field of medicine."
Julia Millington of the ProLife Alliance said: "All human cloning is intrinsically wrong and should be outlawed.
"The creation of cloned human embryos destined for experimentation and subsequent destruction is particularly abhorrent.
"We all welcome advances which enable scientists to halt the progression of motor neurone disease but not at the expense of human embryos."
Professor Richard Gardner, chair of the Royal Society working group on stem cell research and cloning, said the United Nations was meeting to discuss the form of a political declaration on human cloning.
"As national science academies all over the world have stressed, we want to see the message made clear.
"Individual countries should be allowed to make up their own minds about therapeutic cloning, but extending these techniques to attempt to produce a cloned baby is scientifically unsafe, ethically unsound and socially unacceptable."