We have already seen how Lord Winston, the IVF pioneer, has accused the Catholic Church of lying about the HFE bill.
This strategy is known, not just as 'ad hominem', but also as 'obscurantism' - obscuring the facts of the matter to distract people away from the real issue. The real issue is the status of the embryo at the point of conception and the implications of embryo creation techniques for human dignity. Sir Martin claims that human-animal cell hybrids have been produced for many years, and accuses Cardinal O'Brien of ignorance for questioning the ethics of such work. Yet what the HFE bill proposes is not simply mixing human and animal cells to create more cells but creating whole living beings - embryos - which are genetically part-human and part-animal, in different proportions. Sir Martin seems to be using the classic anti-life line that early embryos are just clumps of random, disorganised cells, not whole individuals. Even Sir Martin, however, cannot successfully obscure the truth - he is forced to refer himself to 'embryos', 'embryo form' etc.
We should not be patronised by Sir Martin or cowered by his prominence. There are other experts in the field of stem cell biology with well-founded ethical and scientific objections to the HFE bill. This is not a debate of science vs religion, of academics vs churchmen. This is a debate within ethics, within science and about humanity.