Last night the BBC aired “A Short Stay in Switzerland”, a one-off drama based on the true story of a terminally ill doctor who killed herself in Zurich with the help of Dignitas, an organisation specialising in assisting suicide (read obituary). Assisting a person to commit suicide is illegal in the UK, though there have been several attempts to change the law in recent years.

Dr Anne Turner was diagnosed with progressive supranuclear palsy (PSP), a rare, terrible and incurable brain disease, after her husband had died from a similar long illness. A superb performance from Julie Walters reveals some of the emotions that the real Dr Turner might have had as she made her choice to die. She saw it as a choice between a good death and a bad death. It seemed so reasonable. It seemed so inevitable. It seemed so unreasonable that we do not have Dignitas clinics here is the UK. At the end was a short scene of her son’s wedding in which his mother’s ring is used and a grandchild is seen. Life went on.

What appears to lie at the heart of this story is a question of mental capacity. Did Dr Turner have the mental capacity to decide whether she should live or die? Capacity to make a decision is commonly tested using the framework of Understand-Retain-Balance-Communicate, and this is now incorporated into British law. She was certainly represented as a person who was able to do these things – and we witnessed her communicate her decision clearly at several points. So it’s simple: She had the capacity to decide the issue and it’s not illegal, so what’s the problem?

A judgement over mental capacity is specific to a particular decision, and a person can have the capacity for one decision but not for another. The greater the consequences of a decision, the more certain of the possession of mental capacity the assessor must be. How much capacity must a person have to sanction their own destruction? Is the human mind capable of making such a decision? The question of the natural limits of human understanding has received philosophical attention already: Locke addressed the issue of whether a person could voluntarily sell themselves into slavery in 1690. He concluded that they could not: No-one has that degree of mental capacity. Today the world agrees with him. Might the domain of decisions that no human has the capacity to make include the choosing of death over life?

In any case, mental capacity is not at the heart of this story. It’s a story of value. It’s a story of how much one life is valued in comparison to another. Watch the programme and imagine Dr Turner saying all the same things, but earlier in her illness. What if she had decided the time had come to go to Zurich the day she was diagnosed? Would it all seem so inevitable then? Could it be that the point in her illness at which it becomes easier for you to understand her decision is the point at which her life stops being valued by you? A related programme was broadcast on Sky Real Lives on 10th December last year called “Right to Die?“. Several people approached Dignitas to end their lives, and not all of them were thought to be suitable. Some of them are turned away. There is no suggestion that their mental capacity is impaired, it’s just that the assessors judged that their lives were worth living, and that the other people’s lives were not.

William Lee is a clinical lecturer and MRC training fellow in general hospital psychiatry at the Institute of Psychiatry, London SE5 9RJ