When I was a junior doctor, patients who were dying were often abandoned in side wards, without effective pain and symptom control; terrible deaths were commonplace. In those days euthanasia seemed a temptingly humane solution.

That is not the situation today. Palliative medicine has come of age; and the modern hospice movement has grown from the foundations laid by the late Dame Cicely Saunders, who pioneered the treatment of “total pain” - of mind and soul as well as body. I have been privileged to play a part in this revolution. I have learnt - from patients, their families and colleagues - that care of the dying is far more than diagnosing and treating the physical aspects of terminal illness. That is an important part of the task, and advances in palliative medicine have revolutionised the science of pain and symptom control. Care is also about addressing the wider suffering of incurably ill patients - their anguish at losing personal control of their lives, their failing strength, loss of self-worth and feelings of dependence on others. That is what the discipline of palliative care is about - bringing patient-centred care to the most vulnerable.

Experience of treating many patients over 30 years has convinced me that doctors must accept death as a natural end to life and avoid inappropriate interventions, but that legalising euthanasia, whether indirectly, in the form of assisted suicide, or directly, via lethal injection, is a dangerous step too far.

Proposals to allow “assisted dying”, while undoubtedly well intended, have an air of unreality about them that is worrying to anyone who works with seriously ill people. They assume the existence of a perfect world - a world in which all terminally ill people are entirely clear-headed and make life-or-death decisions on completely rational grounds; and a world in which all doctors know their patients well and have limitless time and skill to assess requests for euthanasia.

The real world of clinical practice just isn't like that. A very small number of terminally ill people are clear about wanting to hasten their own deaths. But we have to think about the great majority who are not. Many move during the course of terminal illness from hope to despair and back again. Depression is a common feature of terminal illness and, as worrying research from Oregon shows, doctors cannot be relied upon to detect it before issuing lethal drugs to potential suicides.

Also important are the feelings of guilt that many terminally ill people feel at the burdens, real or imagined, that their illness may impose on their families. I am not talking about families callously pressuring terminally ill relatives to end their own lives but to hidden pressures that come from within the patient.

Making assisted dying just another end of life “choice” may sound harmless enough, but one patient's choice can easily become another's risk. We don't have a choice about carrying personal firearms, because the end result would be more dangerous for us all. We must balance meeting the wishes of a resolute minority who say that they want to hasten their deaths against the risks of collateral harm to most patients, who want to live, but are vulnerable to wondering if ending their own life might be preferable to dying of their illness. I am in no doubt where that balance of harms lies.

I have come across instances in which an apparently firm resolve to die proves nothing of the sort. In 1991 a young man, a father of three children, was crystal clear in his repeated request to me for euthanasia. His clinical outlook was bleak. Against all predictions, he did not die. Eleven years later his wife died, leaving him to bring up their three children.

In 2006 my own mother was in a hospice bed, in overwhelming pain, repeatedly saying that she wanted help to end her life. This was perhaps the greatest challenge to my view of assisted dying. But my mother was not “helped to die” (the current euphemism) by her doctors. Today, thanks to good hospice care, she lives independently at home despite her cancer and both her life and our lives are enriched.

Doctors who care for terminally ill people sometimes have the subject of assisted dying raised by patients. In most cases they want assurance that they won't be abandoned and will have care that maintains dignity and addresses their deepest fears. To respond by processing a request for assisted suicide risks sending a signal that the doctor agrees that the patient would be better off dead. We rely on our doctors to act at all times in our best interests. That inevitably gives them a degree of influence, however unintended, over the choices we make about our health.

We are told that there would be “safeguards”. But it is clear from overseas experience that applicants for assisted dying get through the net when they should never have been considered. In Oregon, for example, recent research indicates that one in six of those who have had physician-assisted suicide suffered from treatable depression that was not picked up. One reason why we abolished capital punishment 40 years ago was that, very occasionally, we hanged the wrong person. With an assisted dying law, the risk of mistakes is very much greater.

In any case, assisted dying - in the sense in which campaigners use the term - is not something for doctors. Their role is to treat illness where they can and to relieve the distress it brings where they cannot. It doesn't surprise me therefore that the most recent survey of medical opinion has confirmed that most doctors don't believe that “assisted dying” is something they can square with the ethics of good medicine.

Baroness Finlay of Llandaff is an independent crossbench peer, and Professor of Palliative Medicine at Cardiff University

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