Steve Connor: Some time soon, this debate will cease to matter

What often gets lost in the discussion over US legislation on embryonic stem cells is that these laws only apply to government-funded laboratories. The private sector there operates under one of the most permissive regimes in the world.

Bill Clinton wrestled with the topic but shied away from proposing that scientists should be allowed to create human embryos in order to destroy them, which happens when stem cells are extracted. The US Congress intervened and imposed an outright ban on all federal funding. It was left to George Bush in 2001 to come up with a compromise, which allowed US government scientists to work with the limited number of embryonic stem cell lines already created for research.

Meanwhile, the private sector in the US was free to operate as it pleased, provided it did not use government money for its research, and could find its own sources of embryonic stem cells. But this free licence to operate was not particularly meaningful as much of this work is so experimental that few companies wanted to take the financial risk of supporting a long-term research programme, especially when the federally funded climate was so unconducive.

Opposition to the ban grew over the past decade with the help of some high-profile campaigners in favour of research on embryonic stem cells – including the former First Lady Nancy Reagan, whose husband suffered from Alzheimer's disease. There was also the fear that America could lose ground in this vital new area of medical science which promised to revolutionise the treatment of some of the most intractable conditions.

The important point about embryonic stem cells, as opposed to any other kind of stem cell, is that they are truly "pluripotent". They have proven in animal studies to be capable of growing and maturing into any of the more than 200 specialised tissues of the body. Harnessing this pluripotency could mean that diseased organs, from the brain to the pancreas, could be repaired in situ by regenerative medicine. Other kinds of stem cells, such as "adult" stem cells derived, for example, from bone marrow or stem cells derived from umbilical cord blood, have limited regenerative capacity. They do not possess the truly pluripotent capacity of the "gold standard" stem cells derived from early embryos.

But there is a kind of stem cell that has recently emerged. It is created by transforming ordinary adult cells by genetic engineering. These induced pluripotent stem (iPS) cells have been shown in mice to be just as good as embryonic stem cells.

If the same really holds true in humans, and the jury is still out on that one, the arguments about needing spare IVF embryos will eventually go away. However, that day has not yet arrived which means scientists here and in the US will still need human embryos – which means the controversy is not about to go away soon.