Transplantation is now a routine surgical procedure in many countries. Broadly speaking, the number of procedures carried out is linked to a country's economic status - the richer a country, the more transplants take place.

Many countries follow the UK example and operate an 'opt-in' form of consent. Since demand always exceeds supply, this leads to waiting lists and the death of patients while they wait for a donor organ.

To get round this problem, some countries have swapped opt-in for 'presumed consent' (opt-out) approaches - doctors will remove suitable organs after death unless someone has specifically expressed a wish not to be an organ donor.

This may mean that more organs are available, and ensures that organs are used from people in favour of organ donation but not on the organ donor register. On the other hand, it raises ethical questions about the rights we have over our bodies after death, and how we respect the wishes of those who do not want to donate.

Countries operating presumed consent include Spain, Austria, Sweden, France, Chile and Brazil.

Iran has gone further still, and allows the sale of organs. Iranian doctors have claimed that, thanks to live organ donation, there are no longer any waiting lists for liver and kidney transplants (though this has been disputed). Critics argue that this policy puts pressure on poor people to donate organs, potentially harming their health. In some Pakistani villages, 40-50 per cent of adult men have only one kidney, having sold the other for use in rich countries.

China has increased its use of donor organs by taking them from executed prisoners - of around 10 000 transplants a year, perhaps 90 per cent involve organs taken from executed prisoners, without consent. Organisations such as Amnesty International have criticised this practice.

In some countries, cultural taboos restrict the use of transplantation. In China, for example, family members will rarely agree to the removal of organs after death. Israel also has a severe shortage of organs, as some religious leaders do not support organ donation.

Japan has also been slow to introduce transplantation. This originates in the scandal surrounding the world's second heart transplant operation, carried out by a Japanese doctor in 1969. He was responsible for declaring the donor brain dead and also carried out the operation (a conflict of interest now outlawed). When the patient died, the doctor was charged with murder. Japanese culture has also seen the body's 'spirit' as being part of the body as well as the brain, and the concept of brain death is not widely accepted. Heart transplants in Japan did not start until 1999, and even today many Japanese will not donate organs for fear of being declared 'brain dead' while still alive.