Senior scientists have offered to meet Roman Catholic bishops and MPs to explain the need for legislation to allow experiments on embryos that are part-human and part-animal.

Colin Blakemore, a former head of the Medical Research Council (MRC), has invited Catholic church leaders who staged an Easter attack on the Human Fertilisation and Embryology Bill to an “open-minded discussion” with the research community and patient groups.

In a letter to The Times today, Professor Blakemore says that while he does not wish to question the right of Cardinal Cormac Murphy-O’Connor and other senior bishops to speak out on ethical issues, their criticisms are based on misconceptions.

“The Bill is not about creating monsters or mocking the sanctity of human life,” he writes. “Indeed, it will reduce the number of human eggs and embryos used in the production of stem cells for research.

“Scientists should not challenge the spiritual authority of religious leaders, but they are entitled to question the factual evidence on which moral pronouncements are based.”

Professor Blakemore says he would also be happy to arrange for scientists to brief MPs who want a better understanding of the issues before they decide how to vote.

The invitation came after a coalition of medical charities and patient groups wrote to every MP asking them to support the legislation when it is debated in the Commons in May.

The letter, organised by the Association of Medical Research Charities (AMRC) and the Genetic Interest Group, was signed by the chief executives of some of Britain’s leading charities, including Cancer Research UK, Breakthrough Breast Cancer and the British Heart Foundation.

“The Bill will allow new avenues of scientific inquiry to be pursued which could greatly increase our understanding of serious medical conditions affecting millions of people throughout the UK, and ultimately lead to new treatments,” it said.

Human-animal embryos, which are described as human admixed embryos by the Bill, have medical promise because they can be used to create stem cells that are genetically 99.9 per cent identical to patients with conditions such as motor neuron disease, Alzheimer’s or Parkinson’s.

These can be used as powerful laboratory models for studying these disorders and developing new treatments without the need for human eggs that are in short supply.

However, Catholic bishops criticised the Government for refusing to allow Labour MPs a free vote. In Scotland, Cardinal Keith O’Brien used his Easter sermon to brand the Bill a “monstrous attack on human rights, human dignity and human life” which would allow experiments of “Frankenstein proportion”.

Cardinal Cormac Murphy-O’Connor, the spiritual leader of more than four million Catholics in England and Wales, urged Catholic MPs to oppose the legislation, and added his voice to calls for a free vote. “I think Catholics in politics have to act according to their Catholic convictions, so have other Christians, so have other politicians,” he told Sky News yesterday. “There are Catholics who feel very strongly about this matter and I am glad that they do. Certainly, there are some aspects of this Bill on which I believe there ought to be a free vote.”

Three Catholic Cabinet ministers — Ruth Kelly, the Transport Secretary, Des Browne, the Defence Secretary, and Paul Murphy, the Wales Secretary — are reportedly considering resignation if forced to back the Bill.

Alan Johnson, the Health Secretary, said nobody would be forced to support the Bill against their conscience: “There will not be a Cabinet split, but there will be an accommodation for those who have a particular sensitivity around this, including those whose sensitivity relates to the faith.”

No 10 played down reports that “accommodation” meant that Gordon Brown would allow MPs and even ministers the option of voting against the Bill, saying that no final decisions would be taken until nearer the vote.

Mr Brown is privately encouraging scientists to challenge the Catholic Church’s interpretation, and Downing Street insiders say the debate has only just begun. “So far we’ve only heard from one side,” one said.

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