Depression is extremely common. Almost by definition it affects, and alters, our priorities and prejudices and therefore our judgment. Any decision, including an advance directive, made by a psychiatric patient suffering refractory depression is plainly not one made by an individual with the "necessary" mental capacity. A doctor could and should reasonably override such a patient's suicidal intent, so as actively to treat his or her self-harm.

But what of the individual not yet explicitly known to suffer from such depression? Or the overdosing patient bearing an advance directive who is not necessarily clinically depressed, but has received some emotional blow, great or small, which equally distorts judgment? Or even a manipulative 18-year-old with an overdose and a piece of paper? 

Whether these possibilities are all, somewhere in the small print, carefully articulated and excluded in the sub-clauses defining what does and does not constitute a legally binding advance decision, is hardly material: a single tragic death proves the law as currently framed dangerously inadequate. There is an urgent need for an amendment to protect the vulnerable. Advance directives setting out a refusal of treatment for attempted suicide should be intrinsically invalid. (The alternative, surely, is that the deliberately non-treating physician becomes an accomplice to suicide — which is still, just, illegal.) 

But suicide is only one example of what could go wrong. A more prosaic question is simply that of a change of mind. You might believe with perfect confidence that you would refuse chemotherapy in the event of developing severe leukaemia — or any form of medicine if you were paralysed from the neck down — but anticipation is so unreliable. As with depression, so too with any other illnesses: they alter one's perspective. Our zest for life is far greater than we might predict. But the law does not sensitively reflect this: the onus is doggedly on patient autonomy. Its explicit emphasis on individuals retaining the right to make "what might be seen as eccentric or unwise decisions" was surely not intended legally to enshrine decisions so unwise as to be fatally mistaken.

The fact is that most of us find it devastating, if not unimaginable, to contemplate, say, becoming blind, deaf or losing a limb. Equally though, most people who have such problems just get on with their lives. Sadly, some don't. The point is that none of us can predict on which side of this "divide" we might fall. We may like to imagine we are heroes in the making, but we mostly believe we are not. Incidentally, it is surely this deeply unimaginative combination of fear and pessimism that is a driving force for much of the pro-euthanasia movement. But how can we possibly forecast what our attitude might be to some life-or-death decision in such dramatic circumstances? It is this all too human unpredictability that represents a deeper flaw in the whole concept of advance directives.

It is likely that, were any form of limiting amendment concerning advance directives to be introduced in parliament, advocates of euthanasia would not merely offer opposition but would attempt to further their own agenda in additional ways. 

Far better though that such efforts are debated formally by our elected representatives — and probably defeated, judging by past history — than the current worrying trend of legal "clarifications" emerging from a democratically unaccountable judiciary.