Stem cell scientists last night warned patients and doctors to beware of "rogue clinics" that are proliferating round the world, cashing in on publicity about stem cell research by offering unproved therapies at huge cost.

The warning came from the International Society for Stem Cell Research, the field's leading professional organisation, which issued new guidelines for developing safe and effective treatments. These say that stem cell therapy requires expert evaluation, independent oversight, genuinely informed consent of patients and transparent reporting of clinical trial results.