Work on embryos in the UK is overseen by the Human Fertilisation and Embryology Authority (HFEA). Set up when IVF treatment was first developed, it is widely respected and its decisions are often used as a model in other countries. Guidelines drawn up in 1990 are still the basis of all work using embryos, which until very recently had largely been for research into infertility treatments.

In 2002 new laws were passed which made it legal to use spare human embryos from infertility treatments as a source of embryonic stem cells for research into possible therapeutic uses. This can only done under special licences granted by the Government. Therapeutic stem cell cloning is also subject licensing by the Government.

There is an absolute ban on implanting cloned human embryos into a woman – in other words the cloning of whole human beings is completely illegal.

The situation in the US is confused and ever-changing. There is a very active anti-abortion, anti-embryonic research lobby, but many people are very determined to be part of this new science.

At one stage no state funding of any research on embryonic stem cells was permissible – only private research was possible. Recently, state funding has been made available for research using embryonic stem cells which already exist but not on new cells; this ensures that tax payers' money is not used to fund the killing of embryos.

Individual states can have their own different laws – so in California it is now legal to carry out stem cell research including using embryonic stem cells from spare IVF embryos under special licence. In other states scientists would be taken to court for doing exactly the same thing.