The most senior Roman Catholic scientist in Britain has attacked his Church’s opposition to proposed laws that will allow the creation of human-animal embryos for research.

Sir Leszek Borysiewicz made a passionate defence of the Human Fertilisation and Embryology Bill and the science that it will make possible.

He said that the Church was wrong to conduct its campaign in emotive language that misrepresented the nature and purpose of the controversial research.

In an exclusive interview with The Times, Sir Leszek, chief executive of the Medical Research Council, said that in spite of Church teachings on the issue he saw nothing in the experiments or the plans by the Government to regulate them that was incompatible with his faith.

His conscience told him that it was right to support research that promised therapies for devastating diseases such as Parkinson’s and Alzheimer’s, and thus to ease human suffering. He said that many Catholics shared his views.

“I was brought up as a Catholic at home, both my parents are Catholics and I have continued to be a member of the Church,” said Sir Leszek, a vaccine expert who heads the biggest public funding agency for science in Britain. “I go to church but I have had considerable issues with some of the stances the Church has taken on a variety of health-related issues. My conscience tells me very firmly that I should support the Bill as it stands,” he added.

His views are in stark contrast to those of the British Roman Catholic hierarchy, which staged an orchestrated assault on the embryology Bill over the Easter weekend.

The legislation will permit scientists to make admixed human embryos, the main type of which are created by inserting human DNA into empty animal eggs. These are 99.9 per cent human in genetic terms and can be used to make stem cells for studying diseases and developing therapies. It will continue to be illegal to culture these for more than 14 days or to implant them in the womb of a woman or animal.

Cardinal Keith O’Brien, the head of the Church in Scotland, branded the Bill a “monstrous attack on human rights, human dignity and human life” that would allow “experiments of Frankenstein proportion”. Cardinal Cormac Murphy-O’Connor, the spiritual leader of four million Catholics in England and Wales, urged Catholic MPs to vote according to their Catholic convictions and oppose it.

After their intervention Gordon Brown announced that Labour MPs would have a partially free vote on admixed embryos and two other clauses when the Bill is debated in the House of Commons in May. Three Catholic Cabinet ministers were reportedly considering resignation had they been required to support it.

Cardinal O’Brien said last night that he would accept an invitaton from scientists to discuss the Bill.

Sir Leszek, who comes from a Polish Catholic family, said that while he respected the clerics’ right to speak out he disagreed strongly with their opinions and had been disappointed by their intemperate language. “These views are being put forward literally in good faith,” he said. “I don’t happen to share them. The reasons I don’t share them, and obviously I’ve examined my own personal stance on this quite carefully and considered my position, are because of the scientific and therapeutic opportunities that this new legislation will provide. My own balance of judgment is that these outweigh some of the issues that are being raised by the Church.”

He said: “My view would differ from the views that are proposed by the Church on all elements of when life begins. I’m afraid I just differ, just as [views differ] in any large organisation. Maybe that makes be a bad Catholic, but then so be it. These are views I hold in all conscience.

“I don’t believe I’m alone among Catholics. I believe that an organisation such as the Church has to espouse a variety of views and opinions.”

Church leaders, he said, had misrepresented the Bill by ignoring “important safeguards that are built into the legislation.

“I believe this Bill has the right balance. It is really important that people understand what admixed embryos enable us to do. They enable us to develop test-tube models of disease that allow us to look at the nature of a disease such as Alzheimer’s so we can accelerate our understanding of it much more readily than would have been possible otherwise,” he added.

“They will allow us to develop treatments and to screen potential therapies much more readily than would otherwise be the case.”

Professor Colin Blakemore, his predecessor as chief executive of the medical council, said: “I think it is very courageous of him to do this. This demonstrates very vividly that it is possible for practising Catholics to form their own opinions on this subject.”