The human fertilisation and embryos bill is among the most emotive and divisive bills to have come to parliament since its decision to enter the Iraq war. Cabinet ministers - until Gordon Brown allowed, this week, a free vote - indicated they might have to resign rather than vote for it. Rationalists may claim that the bill is simply catching up with the scientific developments of the past few years, but where the very tissues of human life are concerned, nothing is that simple.
The science involved is so advanced that, like it or not, the nitty-gritty of the bill rubs up against some of the most fundamental philosophical questions there are: at what point can life be said to exist?
What choices can be exercised at that point, and who gets to exercise them? Should we go to infinite lengths to cure illness, or is it sometimes more ethical to accept defeat? What does it mean to be a parent? What if there is only one parent? What if there are three? What does it mean to be a child? What does it mean to be human?
Now that there is to be a free vote in May, those who have been lobbying behind the scenes have everything to fight for. So where are the battle lines being drawn and who is on each side?
Embryo research, therapeutic cloning, therapeutic licences
Since 1990, it has been possible to conduct experiments on specially created human embryos - but only in the first 14 days of their existence, when they do not have anything resembling a central nervous system. They are then destroyed. Since 2000, it has also been possible to use these embryos for research into incurable diseases such as Parkinson's, diabetes, muscular dystrophy and motor neurone disease.
The sticking point is the next step: the creation of embryonic stem cell lines that could then be licensed for the ongoing clinical treatment of - as opposed to research into - particular diseases.
This is the holy grail of stem cell research - that healthy cells can be used to replace missing or damaged ones, and thus heal people suffering from currently incurable diseases. At the moment, the Human Fertilisation and Embryology Authority (HFEA), the regulatory body that polices the current act, can't license such use; scientists and doctors, however, argue that it would waste valuable time, and possibly lives, to have to go back to parliament every time such use seemed to be the only option.
For The aspects of embryo research included in the bill are broadly supported by the Medical Research Council, the Wellcome Trust, the Royal Society of Physicians, the British Medical Association, the Royal College of Obstetricians and Gynaecologists, the Academy of Medical Sciences, and the Royal College of Nursing. These groups have everyday, first-hand evidence of incurable suffering, and seek a permissive but highly regulated environment in which such suffering might potentially be eased. They are also supported by more than 200 patient organisations such as Cancer Research UK, the British Heart Foundation, the Parkinson's Disease Society and Diabetes UK.
Against
Bodies such as, most vociferously, the Catholic church, which argue that an embryo at any stage of its development is human - and therefore has an inalienable right to life.
Thus any situation in which embryos are created and destroyed is playing God, unethical and immoral; situations in which embryonic stem cells are created simply to treat other human beings are, further, a commodification of human life. The Catholic church is against most aspects of this bill. It is not necessarily against stem cell research, however, as long as the stem cells are derived from adult tissue.
Embryonic research is opposed, for many of the same reasons, by anti-abortion groups such as Alive and Kicking, and by the all-party parliamentary pro-life group, which works with pro-life outfits such as Life, Care, Core, and the Christian Medical Fellowship.
Proponents of the bill such as Dr Evan Harris, the Liberal Democrat Science spokesman, and a member the commons select committee on innovation, universities, science and skills, believe that some groups, such as the Christian Institute, campaign through the all-party parliamentary pro-life group in order not to appear solely religious-based.
Human animal hybrid embryos
The most contentious part of the bill concerns the creation of so-called animal-human hybrid embryos (referred to in the bill as "admixed" embryos). This is actually already permitted under current legislation and the (HFEA) granted year-long licences in January for scientists to work on creating hybrids. It made the decision after a public consultation lasting several months. If it is adopted, the new bill will formalise this activity by giving it explicit parliamentary approval.
The word hybrid may conjure up images of creatures that are part-human, part-animal, but such images are misleading. The embryos will be prevented by law from developing past 14 days, at which point they are a microscopic ball of cells. Their DNA is more than 99% human. Scientists have lobbied hard for parliamentary backing for hybrids because they say they are essential for advancing stem cell research into Alzheimer's, Parkinson's and type 1 diabetes. At present, to create stem cells for research they need donated human eggs, but there are not enough available to meet demand. Instead of using human eggs it is possible to use animal eggs, for example from cows. The procedure involves inserting a nucleus from an adult human cell into the hollowed out animal egg. The resulting cell contains almost entirely human DNA except for a tiny amount of animal genetic material in structures left behind in the egg called mitochondria. The resulting cell begins dividing like an embryo and scientists can extract stem cells from it for research. The research must occur under licences from the HFEA and it will be illegal to implant it into the womb of a human or animal.
For Because this is basically an answer to a practical problem - the shortage of human eggs - and would fall under all the strict regulations that already govern the use of human eggs in research, all bodies that support embryo research support this aspect of it.
Dr Belinda Cupid of the Motor Neurone Disease Association, for example, has said that there is "currently no cure for motor neurone disease, but allowing the use of hybrid and chimera embryos in scientific research may revolutionise the future treatment of the disease and other degenerative neurological conditions".
Against Cardinal Keith O'Brien used his Easter sermon to denounce experiments of what he called "Frankenstein proportion" and branded the bill a "monstrous attack on human rights, human dignity and human life". Catholics object to the notion of putting human and animal DNA in the same entity and to the notion of creating what they regard as a life for the purposes of research that will then be destroyed.
Mitochondrial transplantation
Mitochondria, found in most human cells, are responsible, among other things, for producing and regulating their chemical energy. Malfunction causes severe childhood illness and often death, and can be passed down through generations. Mitochondrial transplantation would involve removing the nucleus from the egg of the mother and placing it in a donor egg, which would then be fertilised. Chromosomes - which determine the DNA of the child - are located in the nucleus, and so the child would be a true genetic offspring of its two parents - albeit with a few extra bits of mitochondrial DNA from the donor. As Dr Mark Hamilton, chair of the British Fertility Society puts it, "the genetic content of the offspring would be 99.99% from the mother".
For Mitochondrial diseases are "very debilitating, painful and distressing," says Hamilton, who suggests that anyone involved in caring for those affected - one in 10,000 of British children - would want some way for it never to happen again; that in this context a few alien strands of DNA are neither here or there. They would not, for instance, affect a child's appearance.
Against 99.99% is not enough for the detractors, who point out that, in effect, the child would have three parents, two female and one male. What would this mean for the child's identity? Would it have the right to know the identity of the third parent? Does this third parent have rights over the child? Again, the Catholic church, but also anyone who finds the manipulation of gametes, eggs or sperm unacceptable has difficulty with this. "We should not be messing around with the building blocks of life," said Josephine Quintavelle, of Comment on Reproductive Ethics, when it was reported in February that one such embryo had lived for five days.
Saviour siblings
The original 1990 Human Fertilisation and Embryology Act allowed for the creation of so-called "saviour siblings" for children suffering from what it referred to as "life-threatening" conditions. A technique called pre-implantation genetic diagnosis (PGD) allows scientists to select embryos during IVF that are, for example, tissue-matched to a sibling and so would be able to provide compatible tissue to treat the condition. This technique involves extracting a cell from an embryo at the eight-cell stage and conducting genetic tests on it to see if it is compatible. This is typically done on a handful of embryos created by IVF and only genetically compatible embryos are implanted into the mother's uterus.
Saviour siblings have been allowed by the HFEA for treating rare inherited blood disorders in a handful of cases. Britain's first saviour sibling, Jamie Whitaker, was actually conceived in Chicago, after his parents were denied permission to select a tissue-matched embryo. But in 2002, the parents of Zain Hashmi were permitted to select a saviour sibling by IVF who could provide his brother with a bone-marrow transplant that would cure a rare blood disorder called beta thalassaemia. The new bill gives regulators more scope to allow saviour siblings by extending the wording to "serious and potentially life-threatening" conditions. It does not permit embryo selection decisions on the basis of providing a future organ transplant.
For Most parents with terribly ill children will obviously move heaven and earth to keep them alive. Bodies such as the British Fertility Society see no reason why it should not be possible in very carefully controlled cases. In situations where it has been carried out," says Hamilton, "I don't know if the outcome has been anything other than positive."
Against There are serious objections connected to the rights of the created child. Some people do not believe it is ethical to produce a child specifically to save another individual; they worry, with good reason, about straying into the arena of the designer baby. There are also concerns about the psychological impact on the created child. Will it feel as loved and wanted knowing that it was created in order to save another?
Pre-implantation genetic diagnosis
This, a negative variation of the above, involves testing embryos for specific genes and chromosomes - usually for serious inherited diseases - before they are implanted in the womb. It has been possible since the 80s, and is routinely used in IVF, where the embryos can be screened for more than 20 possible conditions. The proposal is to allow extension beyond IVF, where a parent with a hereditary disease or defective gene can have an embryo, or a group of embryos, created outside the body, and then make sure only healthy embryos are implanted. "Most normal, rational creatures want to have children who are fairly healthy," says Willis. "If you're a carrier of a hereditary disease, then clearly you don't want just to take pot luck." Actively choosing "defects" such as deafness is not allowed. Social sex selection - as opposed to sex selection based on the increased likelihood of a particular gender carrying a particular disease - is also banned (creating a rare situation in which the Catholic church agrees).
For The Genetic Interest Group, which represents clinical geneticists, the British Medical Association and the Royal College of Obstetricians and Gynaecologists.
Against Paula Garfield, a theatre director, and her partner, Tomato Lichy, an artist and designer, both deaf, hoped to have the possibility of using IVF to screen for a deaf child. They are outraged that this is not allowed (embryos carrying deafness genes are automatically discarded) because, they argue, it is tantamount to deciding that deaf children are inherently less valuable than children who are not deaf. Again, the Catholic lobby is uncomfortable with taking choice to these extremes. The all-party parliamentary pro-life group also argues against this.
Artificial ('stem cell derived') gametes
This is, essentially, the production of sperm or eggs not from the testes, or ovaries, but from stem cells, which could come from elsewhere in the body - from the skin, for example. Legislation currently allows so-called artificial gametes in research, but bans it for creating a human pregnancy, whereby an artificially created sperm would be allowed to fertilise either a normally created or an artificially created egg and implanted in a woman. Amendments have been suggested that would allow it in certain situations, such as infertility arising from testicular cancer, or chemotherapy.
For The British Medical Association, the Medical Research Council, and the Royal College of Obstetricians and Gynaecologists. Hamilton gives the example of a recent patient of his, a woman in her 20s, who has just had to have both her ovaries removed, and is therefore sterile - unless she is allowed egg donation, or maybe, in the future when such processes have been thoroughly tested, have an egg of her own derived from another cell. "This technology is not here yet, but if you ban it in primary legislation then you're saying it should never happen."
Against Allowing this would, theoretically, open up the possibility of cutting out the need for the opposite sex altogether, because it would be possible to take a woman's cell and grow it into sperm to fertilise her own egg, for example. Quintavalle has called it "the ultimate incest". "Most scientists don't believe that's possible," says Willis, "because you need an X and a Y chromosome. But there is a feeling that if that could be overcome, then let's do without men altogether. Which might be very popular with some groups, but is probably not something parliament should be encouraging."
'Fatherhood' issues
Partly as a consquence of anti-discrimination laws, and the Civil Partnership Act, the bill removes the requirement that fertility clinics take into account a child's "need for a father". It would thus enable lesbian couples and single women to have equal access to fertility treatment. Lesbian couples would legally be allowed to put both names on a birth certificate, without the partner who did not physically give birth having to go through an adoption process.
For The Equality and Human Rights Commission, the Joint Committee on Human Rights, Stonewall, and anyone, such as the Lib Dems, who argues that the "need for a father" is discriminatory against lesbians and solo mothers. Ben Summerskill, chief executive of gay rights group Stonewall, has condemned opponents of the bill for being obsessed with "a few hundred (people) who have an opportunity to have a second loving parent".
Against Religious groups, but also social conservatives who do not necessarily identify as religious are upset by this because they see it as a sign of social decay. There is also the argument - supported by much research - that children with a mother and a father do better in life than those without fathers; however, this research, says Harris, mostly assumes "that the outcomes for children born to solo mothers are the same as those born to teenage mums abandoned by their fathers, or family breakup. The evidence is that the outcome for these children is rather like that for families where the father dies - where there hasn't been conflict, or abandonment, and that otherwise it's not different in terms of outcome from other families."
No father's groups have yet made any representation because the argument is not about access - the issue is whether or not women who have chosen to go it alone, or lesbians, should have equal access to infertility treatment. The Archbishop of York, Dr John Sentamu, warned last year that this amendment was putting the interests of "consumers" who wanted to become parents before the welfare of children. "There is an unpleasant seam of rampant individualism at the heart of this bill," he said, "rooted in a consumerist mentality, where the science that allows something to happen is transformed into the right to have it."
Abortion
The bill does not include abortion, but it is widely expected that it will be used as a vehicle to amend the law on both sides of the debate. Tory backbencher Nadine Dorries, for example, is expected to table an amendment, supported by David Cameron, that would reduce the legal cut-off point from 24 to 20 weeks; there are suggestions that there should be a mandatory two-week cooling off period before any abortion is carried out. There may also be attempts to remove the right to abort seriously deformed foetuses after 24 weeks. Pro-choice campaigners may argue that it should no longer be necessary to have two doctors' signatures for an abortion to occur, and they may attempt a rethink on the law in Northern Ireland.
In any other situation abortion would be quite enough of a flashpoint on its own; the fact that it hasn't attracted quite the attention it might have simply underlines the gravity and scope of the other issues involved.
· Additional reporting by James Randerson.
Having worked with patient groups in supporting the bill thus far we would leave them high and dry if we didn't give them public support on the day that the bill reaches the Commons 
