1. 1I am grateful for helpful criticisms on a previous draft by Derek Bell, Stephen Clark, and two anonymous reviewers.
2. 2The term 'embryo' will be used to refer to the 'human embryo' and to refer to early human lives from the beginning of fertilisation onwards until the eighth week of development. The term 'early embryo' will be used to refer to any embryo below the age of fourteen days.
3. 3Statutory Instrument 2001 No. 188. The Human Fertilisation and Embryology (Research Purposes) Regulations 2001. Norwich. The Stationery Office Limited.
4. 4Chief Medical Officer's Expert Group (Reviewing the Potential of Developments in Stem Cell Research and Cell Nuclear Replacement to Benefit Human Health). 2000.Stem Cell Research: Medical Progress with Responsibility. London: Department of Health; Department of Health. 2000.Government Response to the Recommendations Made in the Chief Medical Officer's Expert Group Report 'Stem Cell Research: Medical Progress with Responsibility'. Norwich. The Stationery Office Limited.
5. 5Chief Medical Officer's Expert Group.Stem Cell Research:Executive Summary: conclusion no 24-25 and recommendation no 1.