By Jonathan Amos
BBC News science reporter, Dublin
Human embryos created using a so-called "virgin conception" technique have been made in the UK for the first time.
Roslin has been at the forefront of embryo manipulation studies
The Roslin Institute, which also cloned Dolly the sheep, reported the creation of parthenotes at a Dublin conference.
They are made by stimulating a human egg to start dividing like an embryo without the addition of any genetic material from a male sperm cell.
The Edinburgh team has so far created six parthenotes to the stage at which they would hope to mine stem cells.
"At the moment we have not managed to get stem cells from these embryos but that continues to be our ambition," Roslin's Dr Paul De Sousa told the British Association's Festival of Science in the Irish capital.
Embryonic stem (ES) cells are "master cells" that in the normal reproductive situation go on to form all of the body's tissues.
The Edinburgh-based team hopes to obtain such cells from the parthenotes and use them to investigate their potential in laboratory research and in medical treatments.
The scientists stress the embryos would never be implanted in a woman's womb - and the terms of their research licence prohibit this anyway.
Parthenogenesis (out of the Greek for "virgin birth") occurs quite naturally in a number of lower animals. Insects such as bees and ants use it to produce their drones. Some larger animals can also reproduce this way - there are a few lizards, for example - but it is rare.
And scientists have induced parthenotes artificially in creatures such as mice and monkeys, although it very often results in abnormal development.
Non-UK work on human parthenogenesis for laboratory research has had very indifferent results so far - and the Roslin team also reports highly inefficient outcomes.
For ES cells to be obtained, an embryo must be grown to the so-called blastocyst stage of about a 100 cells. Roslin's blastocysts achieved about half that, but, with time, Dr De Sousa is hopeful of success.
"It's a numbers game," he said. "It's just a matter of supply of tissue to be engaged in experimentation."
The Roslin team is using eggs in its research programme that have been taken from volunteer donors who have decided to undergo sterilisation.
In normal reproduction, eggs would kick out half their genetic material in preparation to receive the male complement delivered by a sperm cell.
To make parthenotes, therefore, the eggs must be cultured in the lab in such a way that they retain all of their chromosomes. A spark of electricity is then used to initiate the process of embryonic division.
It took Roslin about 300 eggs to get the half-dozen blastocysts.
Some scientists have advocated parthenogenesis on the basis that it could be a more ethically acceptable way to obtain ES cells; working on normal, fertilised embryos is a deeply controversial area.
But others have doubted its use on technical grounds, arguing the degree of genetic manipulation required to achieve parthenogenesis makes this route to ES cells an unnecessarily complicated one.
Even the cloning of human embryos would appear to be a more straightforward approach, they argue.
However, Dr De Sousa believes the infancy of stem cell research means science has to keep its options open.
"I think there are many reasons to be engaged in parallel strands because we don't know that any one of them is going to lead to where we want to go," he said.
Dr De Sousa also believes the research will tell them a great deal about imprinting, the process that controls how genes inherited from the mother and father are switched on and off in the developing embryo.
It is the errors in this process that are thought to lie behind many of the failed attempts to clone embryos.
Groups opposed on moral grounds to this whole area of research reacted with dismay to Friday's announcement.
Matthew O'Gorman, of the charity Life, commented: "It is another example of Frankenstein science which illustrates how out of touch with public opinion these recent scientific developments are.
"[The Roslin team] was granted a licence by an unelected, unaccountable quango," he said, referring to the Human Fertilisation and Embryology Authority, which approved the Roslin research.
Mr O'Gorman said Life was concerned the experiments exploited women, as eggs could only be made available by undergoing treatment that posed a potential risk to health.
Friday's announcement came less than 24 hours after Newcastle researchers said they would be creating embryos using genetic material from three parents - a father and two mothers - as a means of tackling rare diseases.
The "pro-life" groups argued that the latest developments made it clear it was time for reproductive science to be restrained.
Josephine Quintavalle, of Comment on Reproductive Ethics, called on the government to put a moratorium on licences for embryo research.
She said: "We know so little about the mechanics of embryology that at the very least we should wait until we know a lot more until we say we can do it better than nature.
"These are very big steps indeed, and the whole area is running completely out of control."
Mrs Quintavalle said the use of stem cells from discarded umbilical cords offered great potential to cure disease - with none of the ethical difficulties of experimenting on human embryos.