It is altogether misleading to label the current controversy over hybrid embryos as a conflict of religion and science. Doubtless there will be some religious figures who support the government's proposals, but it is also true that there are many scientists who oppose them.

Indeed, the Catholic Church's submission to the Science and Technology Committee Inquiry which preceded the current bill was prepared by scientists and ethicists from the Linacre Centre in London, and the briefing pack distributed to every parish in the UK was prepared by scholars from St Mary's University College, London.

The Catholic Church's opposition to the current legislation is not based on an appeal to abstract theological insights, but rather on a clear and well-established understanding of the dignity of human life and of the perils of tampering with the integrity of human and animal species, an understanding built on solid philosophical grounds.

The recent efforts of the cardinal, archbishop and bishops to push the subject on to the national agenda are the result of a deep frustration that neither ethical nor alternative scientific evidence is being listened to - evidence that would suggest that using adult stem cells can also be effective in the quest for cures for a variety of illnesses and does not involve manufacturing hybrid creatures and killing embryos. Indeed, 70 therapies have been developed already using adult stem-cell technology.

The Church respects both the scientist and the conscientious legislator. And while your correspondents might enjoy the frisson of presenting the Church as a controlling Big Brother institution, it should be remembered that the threat to freedom of conscience emanated not from any episcopal cathedra but from the private office of No 10 Downing Street.

Ronnie Convery, Director of Communications, Archdiocese of Glasgow, 196 Clyde Street, Glasgow.

If it is against the "consciences" of MPs to conduct, for instance, research on human embryos, have abortions or have sexual intercourse with members of their own sex, that is fine. They are not required to do these things.

However, if they want to pass laws to prevent other people from doing them, they need reasons and arguments to justify such infringements of our liberty. That the acts in question are against their "consciences" does not seem to me to count as a relevant reason or argument.

Professor Hugh McLachlan, School of Law and Social Sciences, Glasgow Caledonian University.

It is with an increasing sense of despair that I watch the contributions being made to the hybrid embryo/stem-cell debate and the attack on Cardinal O'Brien for daring to voice dissent on the extravagant claims by scientists as to the possibilities from this research.

This debate is not new. In 2004, when Ronald Reagan died of Alzheimer's, the embryo stem cell lobby launched a campaign to obtain federal funding for research. Then, as now, it was claimed this research held the main hope for Alzheimer's. It took an article in the Washington Post to force scientists to admit this was, in fact, not true. Alzheimer's is a "whole brain" disease, where several different types of cell are affected and it is thought that embryo stem-cell treatment would only be useful for single-cell diseases such as Parkinson's. When scientists were challenged on this, one said that "people need a fairy tale to believe in".

Now the same is happening in Britain. Claims are being made that embryo research holds the key to Alzheimer's, Parkinson's, diabetes, spinal injury and a host of other diseases. But in the 17 years that embryo research has been going, it has not produced one single therapy or treatment.

Adult stem-cell research (where the stem cells are taken from the person being treated and therefore is non-controversial) has already delivered therapies and hope in these diseases. Perhaps the most spectacular of these is the case of Dr Dennis Turner in America, who was treated with his own stem cells for Parkinson's. He went into remission for four years and he was able to go to Africa on safari and was chased up a tree by a rhino. Again, the case of Laura Dominguez, who was paralysed from the neck down after a car accident, and whom doctors said would never walk again, recovered (and walked with assistance and the use of braces) after being treated with adult stem cells. In other areas, adult stem-cell research has delivered. Embryo stem cells have not even got past animal trials. An ethical, viable and spectacularly successful type of research has been sidelined in favour of an unethical, destructive and unproductive one.

Scientists are entitled to ignore the cardinal if they wish. What they are not entitled to ignore is the science of stem-cell research. If they ignore one extremely successful avenue of treatment of disease in favour of an extremely unsuccessful one, they must explain why properly. I look forward to the debate.

Julie McAnulty, Coatbridge.

Dr John O'Dowd states: "The use of such words as monstrous' by Cardinal O'Brien to describe hybrid technologies is misplaced and ignorant." What Cardinal O'Brien actually said was: "This bill represents a monstrous attack on human rights, human dignity and human life."

Dr O'Dowd, in fact, endorses Cardinal O'Brien's call for, as the good doctor puts it, "a rational public debate". Or, as His Eminence said: ". . . the time allowed for debate in parliament and, indeed, in the country at large has been shockingly short. One might say that in our country we are about to have a public government endorsement of experiments of Frankenstein proportions - without many people really being aware of what is going on."

The government is determined that parliamentarians and public alike are to be denied the opportunity for rational debate over such an adequate period of time as to allow all concerned to be helped by the advice of experts on the biology and bioethics involved.

Dr O'Dowd, with a PhD in Pathological Biochemistry, is well able to give us a description of the totally un-Frankensteinian "introduction of somatic (adult) genes into non-human egg-cells" in terms which even I, a humble former teacher of chemistry and biology, can follow.

This is not the whole story. The Human Fertilisation and Embryology Authority says that the legislation has seven "key proposals", the second of which is: "Regulation of interspecies' embryos created from a combination of human and animal genetic material for research."

Not quite what Dr O'Dowd describes in such benign terms; what he has written is ample justification for his own warning: "Our parliamentarians should be careful as to whose words they give the greater weight."

Hugh McLoughlin, Bellshill.

I am surely not alone in noticing the deafening silence from our Church (of Scotland) leaders on the issues of human fertilisation etc. The General Assembly decided in 2006 and 2007 to take a stand against experimentation with human embryos. So why the silence?

Frederick Donald Tosh, Glasgow.