The number of dead donors has remained steady in recent years, but demand for transplants is rising.

This means more and more kidney, liver tissue and single lung transplants are being done with live donors.

Blood relatives offer the best tissue match and the best chance that the transplant will be accepted by the patient's body.

But increasingly other live donors are coming forward, including friends and partners.

Husband to wife

In the last two years, UK doctors have been performing transplants from husband to wife, after US operations started in 1997.

Some 699 spousal transplants have been done in the USA in the last three years, with a 74% success rate.

Only a handful of these operations have been performed in the UK, but experts say they represent a new trend.

Tissue match is not at good as for a blood relative, but an advantage for partners who have had children is that doctors have a better idea of husband to wife transplant success if women have not suffered an adverse reaction to pregnancy.

This is because the woman's body will have already accepted the man's tissue when she became pregnant.

Because of donor shortages and because live donors' organs are generally in a better condition that those of dead donors, doctors are keen to increase spousal transplants.

Bureaucracy

However, they complain that British bureacracy is holding them up.

ULTRA, the body which regulates transplants, has to check out any non-blood related live donors.

This is because it is worried about people being forced to sell their organs for money.

But Paul Jones, transplant coordinator at Addenbrooke's Hospital in Cambridge, says husbands and wives may be better motivated than siblings.

"The partner often wants to help if their husband or wife is disabled and facing an awkward future. It is a good advantage for both," he said.

"It makes much more sense for a husband and wife to donate to each other than for a brother who hasn't seen his sibling for years because he has been out of the country.

"ULTRA does not need to check on him. It seems a bit silly and bureaucratic."

However, the issue of spousal transplants can be emotionally complex.

Often the donor is much more keen than the recipient, who may feel guilty, say experts.

For this reason, most doctors try to give live donors a lot of counselling and time to make a decision.