By Jonathan Amos
BBC News science reporter, Dublin
The potential benefits of embryonic stem cell research have probably been oversold to the public, fertility expert Lord Winston says.
Lord Winston is the current president of the British Association for the Advancement of Science
He fears a backlash if science fails to deliver on some of the "hype" around the cells - as he believes may happen.
He says the notion that a host of cures for serious, degenerative disorders are just around the corner is fanciful.
However, a Cambridge University stem cell researcher said he was certain the work would lead to clinical benefits.
Lord Winston believes some of the uncertainties need to be emphasised.
"Both in Britain and America, huge publicity has been given to stem cells, particularly embryonic stem cells, and the potential they offer," he said in his presidential address to the British Association's Festival Science in Dublin, Ireland, on Monday.
"Of course, the study of stem cells is one of the most exciting areas in biology but I think it is unlikely that embryonic stem cells are likely to be useful in healthcare for a long time."
Stem cells are the body's "master cells" and have the ability to produce all manner of tissues - which has led science to investigate their potential to be used to replace the failed cells responsible for many conditions, such as heart disease and diabetes.
But their desire to source some stem cells from embryos - an ethically controversial area - probably led a number of the field's proponents to hype outcomes just to get liberal legislative approval, Lord Winston claims.
"I was concerned that parliamentarians - particularly in the House of Commons - have been convinced that it was just a matter of a few years before we would be able to transplant stem cells and cure a lot of neurological disorders, like Alzheimer's disease, for which I think it is going to be a hugely difficult problem and probably completely insoluble by stem cells."
Lord Winston said from his own lab's work he could see there were many problems associated with embryonic stem cells that would need to be understood and resolved before they could have clinical applications.
He points to their low cell-cycle time, leading to slow replication in culture and the fact there might be selective pressure for the faster growing, but possibly abnormal cells, to dominate a culture system.
He also highlights the instability of embryonic cells in general and "their remarkable propensity to produce abnormal numbers of chromosomes".
These and other issues, unless resolved, he says, will result in unsuccessful therapies.
Lord Winston does not doubt that study in this area will lead to remarkable and fundamental insights into the workings of the biological cell - and that this should have a huge knock-on effect for medicine with perhaps cancer treatments among the first to benefit.
But he says he does view "the current wave of optimism" about embryonic stem cells and their use in transplant treatments with "growing scepticism".
Commenting on Lord Winston's remarks, Roger Pederson, a professor of regenerative medicine and convenor of the Cambridge Stem Cell Initiative, said it was difficult to be specific about future outcomes given the youthfulness of stem cell study.
However, he told the BBC News website he was confident great gains would be made from the research.
"[Lord Winston's] concerns about the slow pace of the field or the potential downside risks are not at all surprising to somebody actually working in the field. We all think about these questions all the time," he said.
"If you want to know when there will be a clinical impact on the field of diabetes, let's say, I can't answer that question; but I can answer the question, 'will there be a clinical impact?' Yes, there will be; I'm absolutely certain of it - but when exactly and what field that will be in is much harder to speculate about."
Professor Pederson said it was important to consider benefits beyond just transplant therapies.
He said he expected, for example, drug development to make big strides by allowing pharma companies to test novel compounds on specific tissue types derived from stem cells.