Do you carry an organ donor card with you, wherever you go? Do you have it in your wallet or handbag? Yes? Then you are in a small minority.

Only 25 per cent - one in four - of the population of Britain is a registered organ donor. Yet nine out of ten of us support the principle of organ donation.

So why the difference between what we think and what we do? Is it just laziness, or are there deeper fears? Do we just not want to think about our own deaths, or for that matter, other people's? Or do we think, somehow, because of our religious beliefs, that we will need all our organs in a mythical, physical, afterlife?

Whatever our reasons, the practical outcome of all this is that more than a thousand men, women and children die every year in the United Kingdom purely because their doctors can't find organs for them.

There would be more than enough of them if all of the 90 per cent who agree with donation had signed up beforehand. Because they haven't, hundreds of valuable organs are cremated or buried - as are the people who were waiting for them.

It is not as if we don't try to get your agreement. In every doctor's waiting room there are posters asking you to sign up and take a donor card. Receptionists, nurses, doctors all combine to do their best to promote the idea. Yet still three-quarters of you don't do so. So what are we to do?

The first option is to change the emphasis. When we look at the donor card advertisements, the emphasis is on giving our organs in the tragic event of our dying suddenly in hospital after, say, an accident or a brain haemorrhage.

Let's start looking at it in another way. What about considering the other side? We, or one of our nearest and dearest, might be the next person to need a transplant.

Take John, for example. At 28 years old, he had the perfect life. A good job, a wife and three children, all doing well. He hadn't been ill for a day in his life. Then one day he developed a bright red rash over the lower part of his body, and started to feel very unwell. The rash didn't blanch when he pressed a glass to his skin, and that convinced him that it was serious.

His doctor thought so, too. The rash was purpura, in which the small blood vessels in the skin were leaking blood into the tissues - a sign of a severe abnormal immune reaction.

John was admitted to hospital, where it was found that he was in end-stage kidney failure. His kidneys were working at only five per cent of normal capacity.

Intensive care brought him out of immediate danger, but he was left with permanent severe kidney damage, and had to join the 200 people in our region who have to have dialysis three times a week to survive.

A new kidney would make all the difference to him. Yet in the six months since he has been under dialysis, at least a dozen sets of kidneys have been lost that could have helped him or one of the others who dialyse beside him. They could not be retrieved because none of the potential donors, all victims of road accidents or other injuries, had signed up beforehand.

We can't, at present, take organs from people who have died suddenly without permission given either by them before they became mortally ill, or by their relatives at the time of their death.

We do have hospital staff who are trained to ask for permission at such times, but it is very difficult for everyone concerned, and sometimes, of course, there is no-one around to give it.

So I make this very serious plea to everyone who reads this article. If you aren't yet carrying a donor card, please get one the next time you are anywhere they are on offer - in shopping centres or the local surgery.

Register on the NHS donor list. You can do it online, or when you are applying for a driver's licence or a passport. Please don't forget. And once you have your card, make sure it is always with you. When you change your handbag, make it the first thing you transfer into it.

Until we have the Spanish system in which organs can be taken unless the person has opted out of donation, we must rely on your goodwill and your action.

In the meantime, for the sake of John and his friends in the dialysis unit, I will support the Prime Minister's recent initiative. Let's look at the Spanish system seriously with a view to implementing it here. It might be your life that it will save.

You can sign up for the NHS donor list by calling 0845 6060400 or visiting www.uktransplant.org.uk