The scientist who first isolated stem cells more than 25 years ago has hit back at opponents of embryo research.
Professor Sir Martin Evans called their stance "not acceptable", adding that properly regulated research was needed to develop lifesaving treatments.
He urged MPs voting on embryo research legislation to ignore "emotive arguments" from religious groups.
The Nobel laureate will speak at the inaugural conference of the UK National Stem Cell Network in Edinburgh.
Professor Evans, who received the Nobel Prize for medicine last year, told BBC News that opponents of the research were adopting "a public position that was not acceptable".
He urged MPs who will be voting on new legislation to regulate embryo research to "stop listening to the emotive arguments of religiously motivated pressure groups".
He said: "Please look at the evidence. Don't immediately go for the knee-jerk reaction mainly powered by the 'yuck' factor.
"I think the point of debate really is: are the embryos that are being used for research fully-formed humans?
"To me and to many other scientists - knowing that these are just a small bunch of cells - the answer is no."
Sir Martin also rejected recent criticism from the head of the Catholic Church in Scotland, Cardinal Keith O'Brien, who described the creation of animal-human hybrid embryos as unethical and immoral.
He said: "Consider medical advances that have been made and the number of lives that have been saved on the basis of experimentation.
"Very often at the early stages these advances have been objected to and now they are acceptable, moral and proper forms of treatment - take heart transplantation as an example."
Consider medical advances that have been made and the number of lives that have been saved on the basis of experimentation
Professor Sir Martin Evans
Sir Martin acknowledged, however, that scientists had exaggerated the speed at which the research would lead to clinical benefits.
He said: "There has been too much hype and I think scientists are wrong to hype things too much.
"It's understandable - they want their grants, they want to explain to the public why these things need to be done.
"It is inevitable that the full benefits of this technology will take a very long time to come out, but you can see it all there - it would be quite wrong to turn our backs on it all now."
Opponents of animal-human embryos argue not only that they are unethical, but also that they are unlikely to produce useful scientific data.
The Christian Legal Centre and the campaigning group Comment on Reproductive Ethics (Core) have launched a legal bid to overturn a decision to licence scientists in Newcastle and London to create the embryos.
Josephine Quintavalle, of Core, said other forms of stem cell research, such as that using cells from umbilical cord or from adult tissue, were much more likely to produce results.
She said: "There is absolutely nothing to be gained from combining animal and human tissue in this way."
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