The Crown Prosecution Service is considering, yet again, whether to prosecute and possibly imprison otherwise law-abiding Britons for helping their loved ones to die. The parents of Daniel James, a 23-year-old rugby player crippled in a training accident, last month accompanied him to the Dignitas clinic in Switzerland, where assisted suicide is legal. In all hundred such cases so far, the director of public prosecutions has declined to act. The law is clearly unfit for purpose.

This is not regarded by parliament as a sufficient reason for changing the law. Social reform in Britain occurs not when legislators feel it appropriate but when a heart-rending case achieves mass publicity and good people launch a campaign for change. Such has been the case with laws on homosexuality, prostitution, abortion and self-defence - and perhaps one day will apply to recreational drugs. Westminster inertia always holds sway until it is overcome by an infuriated public.

This depends on maintaining a sufficient level of fury. The James case streaked across the media horizon at the weekend, but is fading already. The CPS will probably leave it alone and another opportunity for reform will have passed. Parliament will heave a sigh of relief and return to its fascination with Corfu yachts.

There cannot be a human freedom so personal as ordering the circumstances of one's death. Yet Britain is instinctively collectivist, enveloped in prejudice, religion, taboo and prohibition. We are told how to die by the state, with no consideration for individual choice. The 1961 Suicide Act decriminalised the act of suicide, an inherently absurd diktat, but criminalised any assistance to suicide, thus making it illegal to help somebody do something legal.

The law of death is a shambles. A leading authority on euthanasia, Professor Emily Jackson of the LSE, began a recent lecture on the subject with the sensational question: "What is the most common cause of death in Britain?" Her answer was "death by killing". And who does the killing? "Doctors." One third of all registered deaths are by deliberate morphine overdose and one third by the removal of life support, premeditated acts by medical staff.

All over Britain, families gather every day of the week in hospitals and discuss with doctors how to bring a dignified death to a loved one, often in a turmoil of grief, indecision, exhaustion and shame. The near universal desire "to be allowed to die in my own home" is wilfully disregarded. Parliament's one contribution to this supreme crisis in life's journey is to threaten one and all with suits ranging from negligence to manslaughter.

Now judges are in a position to help. Since they cannot realistically prosecute two thirds of the medical profession, nor it seems the few desperate individuals who take their relatives to Switzerland, judges are on the verge of rewriting the law. The stream of visitors to Dignitas may be breaking the law, yet the CPS has not prosecuted one.

This state of affairs is being tested in the high court by a 45-year-old MS sufferer Debbie Purdy, who has asked that the DPP reveal the criteria on which he exercises his discretion over whether to prosecute, which he refuses to do. She understandably wants to know if her husband is likely to be imprisoned for taking her to Switzerland to die. Can she regard the 1961 act, as it appears, to be akin to the treason and other archaic acts, and defunct in practice?

Purdy is inviting the judicial system to do what parliament has declined to do, which is to define the reasons under which euthanasia will be allowed, if not yet regulated. In this she is supported by a YouGov poll putting support for assisted euthanasia at 86%. A poll for Dignity in Dying records 76% support, and a BMA survey of doctors 56%.

The basis on which the authorities in Switzerland, the Netherlands, Belgium and Oregon allow assisted dying varies. All require evidence of free will on the part of the dying but differ in such preconditions as the possibility of recovery, the extent of pain and the imminence of death.

None has led to an epidemic of "killings". The safeguards seem robust (compared with those governing hospitals). In more than a decade, Oregon has seen just 431 assisted deaths.

The James case, now also under judicial consideration, breaks new ground. The young man's condition was certainly not terminal and his mental state was clear. After a number of failed attempts at suicide, he expressed his wish to escape from "the prison" of his crippled body. He did not want to continue "what he felt was a second-class existence ... in fear and loathing".

He asserted his desire to do something perfectly legal, to take his own life, but was impeded by his disability from doing so. His parents freed him from that impediment. To prosecute them would be an outrage.

Only the most warped collectivist could argue that individuals must be kept alive against their will. One anti-euthanasia lobby last week even insisted that assisted suicide "would deprive the disabled of the benefit of suicide prevention". To honour this spurious benefit, those wishing to die - and their relatives - must endure unbearable suffering at the bidding of others "for the good of society as a whole".

I wonder what kind of society that is. Perhaps it is one that used to ban pain relief in childbirth, banned abortion, and held homosexuality a sin. That this should be supported by such prominent churchmen as the archbishop of Canterbury, the archbishop of Westminster and the chief rabbi is astonishing. In years to come, their attitude will seem not just illiberal but cruel.

I might do everything I can to persuade the victim of a mortal illness or crippling injury to squeeze the last shred from whatever life still has to offer them. I might plead the example of those who have gone that extra mile and enhanced the lives of others thereby. What cannot be right is for me to deny those whose unfettered judgment has reached a wish to die, the freedom of this, the last of life's great dignities.

It is specious to claim that no safeguards can be put in place to protect against abuse. We have safeguards aplenty to regulate such risky social activities as drinking, driving, matrimony and procreation. We can draw up rules to govern the process of dying. This hangover of religious primitivism must surely end. Yet again we must turn to judges rather than members of parliament to uphold a modern liberty.

simon.jenkins@theguardian.com