The Roman Catholic Church has been accused by the government’s fertility watchdog of using “fatal” dogma to oppose all forms of research on embryos and most IVF treatment.

Lisa Jardine, chairwoman of the Human Fertilisation and Embryology Authority, said the church, unlike other religions, had an “insoluble problem” in its fundamental opposition to the destruction of any human embryos, regardless of their stage of development.

Jardine’s comments come on the eve of a controversial parliamentary debate in which Catholic MPs will oppose a government bill to allow the creation of embryos that are partly human and partly animal.

Jardine said: “There is a fatal impediment in Catholicism to all discussion of research on embryos that involves the destruction of embryos at whatever stage. This is not clear to the public in my view.

“The Catholic church is opposed to hybrid embryos, but then it is opposed to all embryonic research. The public hasn’t taken this on board. For the most part, people don’t realise how fundamental this [stance] is.”

Jardine says that once the public understands why scientists wish to create hybrid embryos they approve of the research.

However, Peter Smith, the Catholic Archbishop of Wales, says today in an online article for The Sunday Times that there has been hardly any debate about the creation of “cybrid” (hybrid) embryos. “Will they be human, animal or something in between?” he asks.

The archbishop also challenges the creation of so-called saviour siblings: “Our hearts go out to those parents desperate for a cure for their child dying of a condition that could be cured through a matching donor. But we have to ask about the ethical and social consequences of a law that deliberately sanctions bringing children into the world who may be loved but who have been born in order to be donors.”

Even Sir Liam Donaldson, the chief medical officer, has expressed reservations. He has described full hybrids as “a step too far” and told a parliamentary committee that some scientists felt a “degree of repugnance” at the idea.

The Human Fertilisation and Embryology Bill, which has its second reading tomorrow, seeks to make it legal to create embryos that could be up to 50% animal and 50% human.

One form of hybrid embryo, made up of an animal egg and a human nucleus, would be used to produce stem cells that could be used for research into illnesses such as Parkinson’s disease, multiple sclerosis and motor neurone disease.

After a Commons revolt, Gordon Brown has been forced to allow MPs to vote with their conscience on allowing hybrid embryos and saviour siblings – babies created to donate stem cells, bone marrow or other tissue to a sick brother or sister. The third, unwhipped, vote will decide on removing the requirement that IVF clinics should consider a child’s need for a father when offering fertility treatment.

MPs will also be given free votes on amendments to the bill to change current abortion laws. Nadine Dorries, a Conservative MP, will move an amendment for the upper limit on abortions for social reasons to be reduced from 24 to 20 weeks.

The abortion debate has become so intense that Lord Steel, architect of the current abortion laws, has written to Dorries accusing her of being “juvenile” and lowering the abortion debate to an “inaccurate and trivial level”.

Four years ago Steel believed the upper limit should be cut to as low as 12 weeks for “social abortions”. Steel has revised his view and now states that the 24-week limit should remain, although he would consider a reduction to 22 weeks if an increased proportion of babies born below 24 weeks survived.

Ruth Kelly, the transport secretary and a devout Catholic opposed to the legislation, has been granted leave by Labour party whips to miss the Commons voting.

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