THOU shalt not kill has been a cornerstone of civilisation since Biblical times. But the sanctity of life is called into question when its quality is diminished to unbearable levels.

Margaret John has cancer and fears it may make her existence insufferable, so she is asking for GPs to be free to give advice to patients on drugs that offer a peaceful way out.

Not surprisingly, most doctors are reluctant. Indeed, they surely choose their vocation because they hope to save lives, not help to end them.

That is small comfort to people in Ms John’s position, wary of what the future may hold and wishing to take command of their own destiny.

This week the Supreme Court will debate this most difficult of questions in a once-and-for-all attempt to clarify the issue. It would be wonderful if there were a simple answer, but how could there be?

It would be arrogant for anyone to argue they know how they would react if placed in Ms John’s position, so should society prevent terminally ill patients in dreadful pain or suffering from seeking NHS help to die?

After all, such a service exists elsewhere, for those who can travel, but some will understandably ask why they should have to be put through the ordeal, or be denied the service because they cannot afford to make the trip.

Yet “thou shalt not kill” remains a powerful commandment, and there are other considerations. Might a vulnerable patient feel pressured into taking drastic action because the law does not prevent it, and they feel they are a burden to others?

There are passionate, heartfelt arguments on both sides of this debate and we don’t envy the Supreme Court judges. They have a desperately difficult decision to make.