Professor John Harris, an international authority on bioethics from Manchester University, also called for a change in the law to allow people to sell live organs.

However, his comments have been described as "horrific" by the British Organ Donor Society.

Professor Harris's comments follow a report by a working party of the Royal College of Surgeons (RCS) which warned of a serious shortage of available organs for transplant.

The RCS said there were less than half the number of registered donors needed to meet demand, and that 30% of relatives of people who have died refuse to give permission for their organs to be removed.

Compulsory donation

Professor Harris, a former member of the British Medical Association ethics committee, said people should only be allowed to put a ban on the use of their organs for transplant after they had died for the strongest of reasons.

He could see no reason why religious groups should oppose his views.

He said: "People who listen long enough usually think it is not a bad idea.

"Thousand of people in the UK, and tens of thousands world-wide, are dying because of the shortage of organs. Something radical needs to be done."

Professor Harris said too much emphasis had been placed on the sensitivities of donors and not enough on the needs of those desperately needing transplants.

"Organs should automatically be available for transplant without the need for anyone to carry a donor card.

"People would not have the ability to register objections except for the strongest reasons.

"They would have to explain why they would wish other people to die rather than have their organs used."

The professor said the sale of live organs should be allowed to a single purchaser such as the NHS who would allocate them according to medical priorities, not the ability to pay.

"It would mean there would be none of this buying of organs on the street of Bombay, to be sold in Mayfair," he said.

Doctors favour change

The British Medical Association is officially opposed to the concept of payment for live organ donation, but its ethics committee is calling for a change in the regulations to allow for a system of presumed consent.

The BMA will debate the issue in July

Under this system it would be assumed that a patient's organs could be used for transplant in the event of their death unless they had specified otherwise.

A BMA spokeswoman said the proposal was likely to be debated at the annual conference in July, but could only be sanctioned by government following a full public debate.

She said: "The ethics committee does believe that people should have the right to opt out. There are whole religions that have a fundamental objection to organ donation and we would want that to be respected.

"But the committee does think it is reasonable to make the optimistic assumption that most people are altruistic and that the reason they do not carry a donor card at present may be due to inertia, rather than any specific objection."

'A totally alien notion'

John Evans, chairman of the British Organ Donor Society, was opposed to both Professor Harris's suggestions.

He said: "It would be wrong to say a body belongs to the nation to do with whatever it likes. It would be completely alien to the culture of the land.

"It is important that a patient's relatives are involved in any decision about organ donation, and that they are shown the proper care and concern that should be given to somebody who has experienced a bereavement."

Mr Evans said doctors also needed to feel sure that they had the backing of a patient's family before removing organs, a procedure that was often emotionally draining for the doctor involved.

He said the best way to tackle the shortage of donor organs was to improvement public education about the issue. Personal assault legislation which prevented the removal of organs from some patients should also be scrapped.