Ian Wilmut, the scientist who cloned Dolly the sheep, has applied for a government licence to work with human eggs in an experiment that prepares the way for human cloning.
Professor Wilmut's application to the Human Fertilisation and Embryology Authority (HFEA) covers a technique in which an unfertilised egg is stimulated in the laboratory to develop into an early embryo. The procedure is called parthenogenesis, which literally means "virgin birth" and results in cloned embryos that develop without the need for sperm to fertilise an egg.
Experts say that knowledge gleaned from the procedure will be invaluable for doing the sort of cloning that led to Dolly, where genetic material is transferred from an adult cell into an "empty", unfertilised egg.
Professor Wilmut's laboratory at the Roslin Institute near Edinburgh will not, however, allow "parthenogenically activated" human eggs to be implanted into the womb, which is illegal in Britain.
The institute's application says the research aims to grow the human embryos in a test tube to a few days old, when the scientists can extract embryonic stem cells for study.
Professor Wilmut was unavailable this weekend but Harry Griffin, acting director of the Roslin, said the institute had formally requested legal approval to work with human eggs. "We can confirm that we have made an application to the HFEA for a licence under the Act but we're not prepared to comment on the details of an on-going process," he said.
Professor Wilmut said last month that he hoped to apply for a licence to start work on Dolly-type cloning using human eggs within six months. He did not mention that he had already prepared an application to do parthenogenic cloning.
Earlier this year, scientists from Advanced Cell Technology, an American biotechnology company in Massachusetts, announced they had successfully extracted embryonic stem cells from monkey embryos created by parthenogenesis.
Robert Lanza, of the Massachusetts team, said that by carrying out parthenogenic-activation of human eggs, Professor Wilmut would gather important insights necessary to do Dolly-type cloning on human eggs. "In the field of cloning, before you proceed with nuclear transfer of any species, you need to work out the activation protocol. Essentially that is learning how to fool the egg into thinking it is fertilised," Dr Lanza said.
Creating human embryos by parthenogenesis may circumvent many ethical concerns of generating embryos by the Dolly technique. In the US, the embryos made by parthenogenesis are not even considered embryos by some scientists, who call them "parthenotes". There is also the question of whether they are considered embryos under the 1990 Act, which defines an embryo as an egg fertilised by a sperm.
In mammals, parthenogenic embryos rarely survive beyond early development. Dr Lanza said the monkey stem cells from parthenogenically activated eggs grew into an array of specialised tissues, which could, in humans, help patients with illnesses such as Parkinson's disease.
The chomosomes of such cells would all derive from one woman, leading to hidden complications resulting from a genetic process called imprinting which carefully controls the pairs of maternal and paternal genes in a naturally fertilised egg. This is why some see the Roslin application as a prelude to the more controversial Dolly-type cloning, which aims to produce embryos that would provide more suitable stem cells for tissue transplants.
The HFEA is likely to decide on Professor Wilmut's application early next year.
By Steve Connor, Science Editor