Foetal and embryonic cells have already been used to try to repair nerve damage in people with Parkinson's disease, multiple sclerosis or following a stroke. In the 1980s British doctors were among the first to transplant foetal tissue into the brains of people with Parkinson's disease in an effort to replace the dopamine-producing cells which had died.

Results were mixed and, since the British public seemed unready for such research, most of the work went abroad.

But in the new climate of tolerance, researchers at the British biotech company ReNeuron are gearing up to use stem cells grown in the laboratory from foetal tissue to repair brain damage following strokes. They have already demonstrated significant improvements in movement in rats with stroke-related paralysis. Human trials are also starting in the US using embryonic stem cells to make the myelin-producing nerve cells which are damaged in people with MS. Again, animal studies have been promising. Other targets for the future will be Parkinson's and Alzheimer's diseases. As in strokes and MS, the aim will be to inject large numbers of stem cells capable of differentiating into the type of brain cells which are destroyed.