Human Fertilisation and Embryology Bill kicks up furious opposition in UK. Even Labour MPs are calling for a free vote.
Thurrock MP Andrew Mackinlay has lashed out at Government Chief Whip Geoff Hoon Hoon saying his refusal to allow Labour MPs to oppose the Embryo Bill on the grounds of conscience was "an insult to the intelligence."
It clearly showed that Ministers were "totally out of touch" with public opinion, Mackinlay maintained..
The bill includes provisions for the use of animal-human hybrid embryos in experiments. Screening to create so-called saviour siblings, those with a tissue match to existing children who require a donation of stem cells, bone marrow or even organs, will be allowed.
Doctors will be permitted to screen embryos for disease or disability. The "need for a father" test, previously applied by fertility doctors when treating single women or lesbian couples, will be scrapped. Amendments to reduce the upper limit for abortions from 24 to 20 weeks and permit the use of artificial sperm or eggs will be considered.
There are certainly powerful voices in support. Of Liz Shipley's for instance. She is suffering from motor neurone disease (MND). The 36-year-old from Newcastle had lost her mother to the same condition when she was just three years old. Several other members of her family, including her sister and uncle, had died or were suffering from the muscle-wasting disease.
Ten years on and unable to walk, write or dress herself, she fears that her two teenage children will also inherit the disease. Shipley does not expect a cure in her lifetime but she backs controversial scientific research using embryos that are part-human, part-animal, which could lead to a treatment for her children if they are struck down.
"When you have an illness for which there is no cure, you have to investigate every avenue," said Shipley. "I do not want my children to be told in 20 years' time that they have MND and there is still no cure. I believe the answers will lie in stem cells of some kind. Hopefully this research will be able to tell us why this is happening to our family."
For Shipley and campaigners such as the Motor Neurone Disease Association, the new legislation heading for the House of Commons this spring is simply a matter of putting in place the best infrastructure for scientists to help people like her.
But for others it will be the most controversial bill of this parliament with the science it allows running far ahead of what many would regard as reasonable.
Rowan Williams, the Archbishop of Canterbury, said that the country lacked a "clear moral perspective" on such issues.
The Human Fertilisation and Embryology Bill is designed to regulate just how far scientists can go when experimenting on embryos or embryo parts. It will also lay down new boundaries for fertility clinics, setting out the circumstances in which controversial techniques for screening embryos for defects, or gender, are allowed.
Even Sir Liam Donaldson, the chief medical officer, seems to have reservations. He has spoken of the human-animal hybrids on which Shipley is placing her hopes as a "step too far", warning that even scientists feel a "degree of repugnance" at the idea.
It is too late for ministers to back down: the legislation was in the Queen's speech and is strongly supported by Gordon Brown.
The bill could create a freedom of action for fertility scientists that is unparalleled in the developed world. Some say it goes much further than enshrining current practice in law.
"We don't know at this stage where the breakthroughs will come from, but it wouldn't be sensible to close off research in these areas," was how a health department official described the bill's principles.
Among the most controversial proposals is to allow the creation of hybrid embryos. The government says these could solve the shortage of human eggs needed for research into curing diseases such as Parkinson's and MND.
One form of hybrid embryo, made up of an animal egg and a human nucleus, could be used to produce stem cells. These are valued by scientists because they are more flexible than other types of cell and consequently more useful for research. The hybrids, which could be up to 50% animal and 50% human, would be allowed to live for only 14 days.
"This is not about creating monsters," say officials. "It's purely laboratory research."
The potential creation of such embryos has angered religious groups, which object to the manipulation of a life form that is at least part-human. "We haven't as a society got a sufficiently clear notion of what constitutes a human organism," said Williams. "My own view is that an embryo is a human organism, but that requires some argument, which isn't something that can be settled by science alone."
Some scientists have also voiced their reservations. Last year Donaldson told a parliamentary committee set up to scrutinise the legislation: "On the question of full-blown hybrids being created between animal gametes and human gametes, there was a degree of repugnance, even among scientists . . .
"It was felt - and I think is still felt - that this would be something where there was no clear scientific benefit and, secondly, a feeling that this would be a step too far as far as the public is concerned."
Some scientists ask whether the legislation not only moves too far and too fast but also in the wrong direction. They question whether such hybrids are even necessary because stem cells derived from a patient's own body are already being used to treat disease.
Colin McGuckin, professor of regenerative medicine at Newcastle University, has shown that stem cells taken from the umbilical cord of a newborn baby can be transformed into skin and liver tissue. "There are many types of stem cells available to develop new drug therapies and I think the overemphasis in our country on embryonic stem cells is disappointing," he said.
In November last year Professor Shinya Yamanaka, of Kyoto University, Japan, announced that he had successfully reprogrammed skin cells into embryonic-like cells, possibly making the use of material from embryos unnecessary.
Hybrids are just one of many controversial areas. The bill also enshrines in law the creation through in vitro fertilisation (IVF) of babies that are a suitable tissue match to help to treat an existing child, the so-called "saviour siblings".
Here the act again goes further than existing practice in suggesting that children could be created to donate part of an organ, as well as bone marrow, to their siblings. This, too, has triggered angry opposition.
"For children apparently to be created for the sole and explicit purpose of being available to provide any type of tissue at all for an existing sibling is appalling," said Lord Alton, the independent peer. "This is truly dehumanising society."
The act also allows fertility clinics to discard, or "screen out", embryos suffering from serious diseases. This has angered extremist disability campaigners who want to turn the legislation on its head by allowing fertility clinics to screen in embryos carrying genetic abnormalities.
Stoking an already raging fire are two opposition MPs who are preparing to lay down amendments guaranteed to make it even more contentious. Evan Harris, a former doctor, wants scientists to be able to create artificial sperm - potentially solving the national shortage of sperm donors and allowing cancer survivors who are infertile to have children. Opponents describe it as "playing God with human DNA", while Harris insists that it is "rational and progressive".
The prime minister regards the legislation as crucial. If Britain does not make it easier for scientists to carry out pioneering research, he fears they will go elsewhere, jeopardising the country's international reputation as a centre of excellence in such work. His interest is not just political but also personal. His son James suffers from cystic fibrosis, one of the conditions for which stem cell research offers real hope.
Several members of Brown's cabinet are staunch Catholics. Ruth Kelly, the transport secretary, Des Browne, the defence secretary, and Paul Murphy, the Welsh secretary, are vehemently opposed to the use of embryos for research.