It is a question no parent would want to be asked if their child was dying: would you allow their organs to be used for transplant to save other lives? Yet that is the traumatic decision Lauren McDiarmid and her husband, Donald, were faced with as they sat with their 17-year-old son David, who was on a life-support system in a ward in a Glasgow hospital after suffering a brain haemorrhage.

Lauren, from Dunbartonshire, had not yet been told that her son was effectively brain dead when the transplant question was raised.

"It was absolutely horrendous," she says. "It was the worst experience. To watch your son die and then having to make a decision like that was awful. Really, really awful."

Lauren, 45, is one of a growing number of people who are fighting the Scottish Executive's move to shun plans for "presumed consent" with regard to organ donation. The proposals, aimed at averting a transplant "crisis", would ensure everyone is treated as a potential organ donor on their death unless they expressly requested not to.

The chief medical officer for England and Wales, Sir Liam Donaldson, is proposing legislation to change the system of organ donation so that people would have to opt out, a move prompted by revelations that the NHS needs three times the number of donors it currently has on its register. But the Scottish Executive said it had found there was not enough support for such a move and that it could make organ donation more complicated.

Studies reveal that 70% of people want to donate their organs after death, but only 20% are on the organ donor register.

More than 50 Scots die annually waiting for an organ transplant and NHS figures show that waiting times for kidney transplants at Scottish hospitals are among the highest in the UK.

Lauren, who lives in Bonhill, Alexandria, says that she would still have wanted to be consulted over organ donation as she believes that youngsters under 18 are not old enough to make the decision to opt out. But she says presumed consent should be in place for those over 18.

Her trauma began when her son was admitted to the Southern General Hospital one Sunday in June 2004, after an aneurysm the size of a strawberry - which developed from a weakness in the main artery of his brain - burst. There was no possible treatment.

For five days, while on life support, he would lose consciousness and then show some response that gave the family hope. The following Friday, he stopped responding and never regained consciousness.

Sitting at his bedside throughout, Lauren and her 45-year-old husband, Donald, a taxi driver, feared the worst. "I had never seen anybody die before. As I was sitting with him, I said to the nurse: is he going to make it?' She said she did not think so.

"I sat with him for a while and wondered what I was going to do. Then she talked about doing the brain stem tests, while he was still breathing on life support, which would detect whether he was brain dead.

"Just before they did one of the tests, one of the nurses asked whether David carried an organ donor card," she says. "I said no, he was only 17. She said, depending on the results of the next test which would show if he was brain dead, if we decided to opt for organ donation they don't switch the machines off, they just write down the time of death. If you don't decide to do organ donation they switch the machines off there and then. And that's it, finished.

"I said I would agree to organ donation," Lauren adds. "They were really nice about it. The request was all done very tastefully and tactfully.

Lauren was given leaflets about the procedure, and after reading them she decided to speak to a minister. "I am not a religious person but I felt I needed to speak to someone because I was worried that if there was another life, does he really need his organs," she says. "That's just the way I was thinking at the time. What he said was that there were no religions that were against organ donation.

"My opinion then was that if my son was dying and he needed a heart or lungs and someone in the next bed had died and you were asked do you want that heart and lungs', you would say yes, wouldn't you? I knew my son and I knew that he would have wanted his organs used to save others. He was a caring person.

"We got a form as the brain test was done which asked what we agreed to have done and what we didn't agree to. But it was still harrowing."

Lauren agreed that all vital organs, including heart, lungs, liver, pancreas and kidneys could be used, but not his eyes or any of his face, which still gave an illusion of life. "I would not bear anyone to touch his face," she explains. "I just had a thing about it, it was his eyes, after all. If it was myself, I would just say just take them, but when it's your child you think, I don't want you to touch his face."

His pancreas and one kidney went to one person; for confidentiality reasons, the couple know only the recipient's age, sex and town of residence, all of which was bittersweet for Mrs McDiarmid. "I thought that was really, really good but I felt a bit sad as well."

His heart went to a child but there were problems after the transplant and she admits that she did not want to know if the child had died. His lungs went to save a patient in England. She has also had a few letters from a lady of 60 from England who is alive thanks to David's liver.

"I feel like now there is a point to his death," she says. But she admits that it is too early to meet any people that have benefited from her son's organs.

"I don't know what I would feel if they came to my door. I don't think I am ready to meet these people. I know people do meet those who have benefited from organ donations but it is usually years down the line.

"We are only three years into this and it would be too difficult. We still have emotional times."

WHEN we speak, she explains how the family are preparing to celebrate the 18th birthday of her other son, Donald. It's a celebration that has extra significance for Mrs McDiarmid.

"For us, that is a big hurdle because David died when he was 17. I always thought, what about my other son', who was 14 then, whether something was going to happen to him. But he is 18. So it is a big relief."

Presumed consent, she says, would mean that the trauma of families being asked by the medical profession about whether their loved one's organs can be used, will disappear.

"It would be easier because they don't have to say to you, like in my case when they are doing a brain stem test, about organ donation. The test is a big thing to deal with and then you are bombarded with all this at once.

"I would not say I would be totally happy that someone else would have made the decision instead of the family in our case. But I think it is different when you are talking about a child. I don't think decisions should be made for children. Once they are 18 they can make their own decision and opt out if they don't want to be donors."

She believes that there should be more discussion about organ donation in schools to ensure there is full awareness.

"The Scottish Executive may say that there is little support for presumed consent, but did they ask the parents of people who have to agree in such circumstances?

"I know that, for myself, it would be easier if everyone was considered a donor unless you opt out. But I know that it is a complicated situation and requires a lot more discussion.

"There is a problem that people don't know that they are going to die. They don't think about it. So they don't think about organ donation. Which is why awareness exercises, especially in schools, are very important.

"At the end of the day, as I wish David had never died, I don't wish I had not agreed to the organ donation, although I relive what happened in the Southern General every single day my life."