It seems almost obligatory to add the word controversial to any article on stem-cell research. The most clear cut issues are those regarding the use of embryonic stems cells.

These are powerful as they have the potential to produce any tissue in the human body. But at present they can be obtained only from a human embryo, which is destroyed in the process. Many argue that this is the destruction of a potential human being and object on religious as well as other ethical grounds.

For John Harris, though, the real ethical issue is the restriction of embryonic stem-cell research by what he sees as lesser concerns.

Harris, the Sir David Alliance Professor of Bioethics at the University of Manchester, argues that the status of the embryo is misplaced. Human reproduction is only 20 per cent efficient, so for every baby that is born four embryos are created and perish. Many are created and discarded in fertility treatments. Is it, Harris asks, less frivolous to create embryos to treat the sick than to produce a family? Saving existing lives must be as important as creating new lives. It is unethical to stand in its way.

One of the interesting but possibly confusing aspects of stem-cell research is its potential to move the ethical goalposts. Thomas Baldwin, professor of philosophy at the University of York, illustrates this with some recent Japanese research. It demonstrated that it might be possible to take a fully differentiated adult cell and run its biological clock backwards until it reaches an embryonic state.

The question is, can this cell then act as an embryo and produce a fully functioning human? If it can, then it means that every cell in the human body has the potential to become another human and, at a stroke, removes the unique status of the embryo.

Rewinding adult cells to embryonic stem cells is the goal of many researchers. It would present no ethical problems as no embryos would be involved in their production. But the only way to know whether these adult-derived cells, known as induced pluripotent stem cells, really do have all the desired properties is to compare them with the genuine embryonic version. So while they offer an ethically simple future, getting there involves the same ethical concerns as embryo research.

The final twist in this tale is that if new humans are created using this technology then this is reproductive cloning, something Baldwin thinks is highly undesirable.

While most of the ethical focus is on the embryo there are other types of stem-cell research that raise ethical questions. For example, a common source of foetal cells is umbilical cord blood. It is painless to take and normally discarded. But it needs to be harvested at birth and it has, Baldwin says, turned out to be surprisingly difficult to organise taking cord blood in a way that does not affect the birth.

Baldwin was deputy chief executive of the Human Fertilisation and Embryology Authority (HFEA), which regulates all embryonic stem-cell research.

Harris is a critic of some of the HFEA’s decisions but is adamant that regulation is essential. This is a complex and emotive issue with no clear-cut answers. What there is, Baldwin says, is an open debate in this country, something we should be proud of.