Controversial and powerful – stem cells, it seems, are the rock stars of science. They are rarely out of the headlines, but why are stem cells so contentious, and will they live up to their promise of providing cures for a vast range of diseases?

Embryonic stem cells are the master cells of the body, capable of forming any type of human cell. Scientists believe that this unique ability makes them ideal tools for studying disease, and developing new treatments. For instance, researchers are investigating whether they can turn stem cells into brain cells, to replace those lost in Parkinson’s disease.

Further, by turning stem cells into, say, lung cells, scientists can use them to discover what goes wrong in the course of certain diseases, such as cystic fibrosis.

Adult stem cells also exist; we have clusters in various parts of our body, such as the brain, bone marrow and muscle. They repair wear and tear by forming new cells to replace those that are damaged or dying. Scientists hope to discover a way of beefing up our adult stem cells to enable them to repair more substantial damage, such as that sustained during a stroke.

However, the cells have their limitations. Unlike embryonic stem cells, they can form only the type of body part, or tissue, that they reside in. Brain stem cells can make only brain cells, and the stem cells found in the muscle can make only new muscle cells.

Embryonic stem cells are steeped in controversy. Researchers obtain them from very early embryos, when they are five to six days old and about the size of a full stop. The embryos are left over from IVF procedures, and would otherwise be destroyed. Instead, they are donated to research with the consent of the donors.

But the process of extracting the cells destroys the embryo, and some people believe that this constitutes the destruction of human life. Pro-life organisations and certain religious groups vocally object to the research.

There may, however, be a way of generating embryonic stem cells without destroying embryos. Researchers in Japan have announced that they have devised a method of turning back the biological clock of a fully formed adult cell, and reverting it to an embryonic stem cell. This could dispense with the need for embryos, although the work is still in the early stages.

Scientists believe that we should investigate both adult and embryonic stem cells, as both hold great therapeutic potential.

Research on human embryos is heavily regulated in the UK, but the laws are set for an overhaul. The current regulations are 18 years old: most scientists feel they are out of date and do not reflect current scientific capabilities. A new set of regulations are outlined in the Human Fertility and Embryology Bill, set to air in the House of Commons on Monday.

The Bill has provoked huge controversy, as it could give the green light to the creation of human-animal embryos, or human admixed embryos. These are made by replacing the DNA in an animal egg with human DNA. The resultant embryo would be 99.9 per cent genetically human. Why do this? Well, the human DNA could, for example, come from an Alzheimer’s patient, and scientists could then use the extracted embryonic stem cells to find new treatments. Animal eggs are favoured over human eggs as the latter are hard to obtain.

New stem-cell technologies will provoke heated debate, yet most scientists welcome such discussions.

Dr Robin Lovell-Badge, a stem-cell scientist from the National Institute for Medical Research, says: “It’s very important to keep the public on the side of science, otherwise we may lose the political debate before it gets started. For example with GM foods, scientists took way too long to respond to scare stories about GM foods, and we still haven’t recovered from that.”

Dr Stephen Minger, from King’s College London, was one of the first scientists to receive a UK licence to work on embryonic stem cells. He echoes the need for keeping people informed, and letting them weigh up the pros and cons.

“On the one hand there are the ethical and moral issues around using human embryos in research, but at the same time there’s a public fascination with what may come out of this, in terms of therapies and drugs. I think the work will revolutionise medicine.”