HOPES of transforming medicine with stem cell treatments in the next decade have been "hyped up", one of the country's leading fertility experts has claimed.
Lord Winston said research on embryonic stem cells was worthwhile and likely to yield important new information about cell biology and cancer.
But he said it was premature to talk of exciting new cures for diseases such as Parkinson's and diabetes. Lord Winston criticised the scientific establishment for exaggerating the potential of stem cells, and highlighted major obstacles that still had to be overcome.
Speaking on the eve of this year's British Association Festival of Science, starting in Dublin today, Lord Winston said: "Science is not about certainty, but uncertainty.
I think we need to be considerably more modest about our science. We do tend to hype up so many activities. The latest one in biology is the issue of embryonic stem cells. I view the current wave of optimism about embryonic stem cells with growing suspicion."
Stem cells are immature cells that can be programmed to perform different functions. Those harvested from early-stage human embryos have the potential to become any kind of tissue in the body.
Scientists are looking into ways of growing the cells and directing their development.
Experts have predicted that in future this will lead to replacement tissue treatments for curing degenerative diseases or repairing injuries. Stem cells could be used, for instance, to replace lost brain neurons in a person with Parkinson's or Alzheimer's, or renew pancreatic insulin-secreting cells in a patient with type 1 diabetes.
The first treatments could be ten years away, or even sooner, it has been claimed.
But Lord Winston, president of the British Association for the Advancement of Science, and Professor of Fertility Studies at Imperial College London, is not convinced.
One of the biggest problems, he said, was that cultured stem cells are inherently unstable. When grown in the laboratory, they often produced cells with chromosomal abnormalities.
They also replicated slowly - so slowly that by the time they would be ready for use as a tailor-made treatment, the recipient patient could be overcome by disease.
Ensuring that all the cells being used for treatment did the job they were supposed to do was another problem.
In culture, cells did not develop in exactly the same way they did in the body where they were subject to a complex interplay of genetic influences.