Seventy years ago today, a quarter of a mile from where I am writing, Sigmund Freud’s doctor, Max Schur, administered a third and final shot of morphine to his celebrated patient. The previous day Freud, suffering from a terminal recurrence of the jaw cancer that had cost him half his palate, and smelling so badly that his beloved dog would come nowhere near him, reminded the doctor of an earlier conversation.

“My dear Schur,” he said, “you certainly remember our first talk. You promised me then not to forsake me when the time comes. Now it is nothing but torture and makes no sense any more.” In consultation with Freud’s daughter, Anna, Schur acceded to Freud’s request and gave the first injection of three centigrams of morphine. In the early morning of September 23, 1939, Freud died.

Tomorrow, also September 23, after the Debbie Purdy case, the Director of Public Prosecutions is expected to publish new draft guidelines about the circumstances under which it might prosecute those who assist (as Schur and Anna Freud did) someone to commit suicide. Except that these new guidelines will apply only to those who travel to a jurisdiction where assisted suicide is legal. In Britain it is not. Seven decades later the actions of Freud’s doctor and beloved daughter — actions occasioned by compassion and love — will still be illegal.

In July even such limited reform as was suggested by Lord Falconer of Thoroton to the laws forbidding assisted suicide abroad was defeated in the House of Lords. During the debate, an opponent, Lord Walton of Detchant, an 87-year-old former neurologist, repeated a convenient classification. If, in attempting to cure or alleviate pain, a physician were to shorten life, that would be all right, “but the intention must not be to kill”. This was a principle “that had served the medical profession well over many years”.

Perhaps so, but not because of its honesty. Schur would have been better off (under Walton’s law) had Freud said nothing about his wishes and had no conversation taken place with Anna. Then he could have operated in the shadows, free from the suggestion that he had intended to carry out Freud’s request, and deliberately ended his life. A lie would have been safer than the truth.

It isn’t surprising, when you think about it, that many of us increasingly favour Schur over Lord Walton. Past ambiguities about what you could and couldn’t do tended to favour those whose job it was to interpret them — usually the priestly classes of the professions. But over the years we have come increasingly to believe that our judgments about ourselves, albeit as informed by some experts, have a sovereign quality. We have gradually applied this to our clothing, our sexual existences, our capacity to choose and change partners, our fertility, our spiritual beliefs — and now, inevitably, to our deaths. The choice to do as Freud did, to say: “I want to die now, please help me,” is no more or less than the choice that I want for myself. And even that understates it, I realise, because it is the choice that I now demand.

The sheer amount of life available to us in the West might explain some of this trend: 100 years ago most men my age were dead. The Office for National Statistics projects that a boy born in 2006 will live, on average, to be 88.1, and a girl 91.5. Fending off death is no longer the constant struggle it once was — and perhaps exercising autonomy over the circumstances of one’s departure looms larger. Maybe we are just more aware of the possibilities.

So why should we not have the right to determine, within reason, when and how we die? Some religious people will say, in essence, because God says so. But one may observe that sometimes God so invoked seems to have served mankind well (as over opposition to eugenics) and sometimes badly (as over, say, family planning). Church folk will forgive me for addressing some of the more secular objections raised in July’s Lords debate.

First there was the point made by Lord Mackay of Clashfern, that “any proposal to alter the current position involves a judgment that a certain kind of life, or a certain span of life, has become unworthy of support from [the] principle [of the sanctity of life]”. To which I reply: “No, it doesn’t.” What a proposal might do is to permit the liver of a life to decide its value — not Lord Mackay, me or the Archbishop of Canterbury.

Second came the argument primarily advanced by Baroness Campbell of Surbiton, that permitting assisted suicide sent a message to the “disabled and terminally ill” that their lives were somehow second-rate. “Is this really the future we wish to offer those who become terminally ill?” she demanded. But this essentially requires that some people forgo a concrete right of self-dominion for the sake of a speculative (and avoidable) impact on others. If society made decisions on this basis, we would choose who was and who wasn’t permitted to have and bring up children.

Third, and related, was the contention, advanced by many, from the Bishop of Exeter to Baroness Kennedy of The Shaws that the law ought not to be changed because people would either feel “pressured into dying” or actually would be pressured into dying.

Both said that the “vulnerable” might be insufficiently robust to resist the die-soon atmospherics emitted by relatives, knowingly or not. “People who have not led assertive lives, exercising their own choices,” the Bishop said, without any obvious irony, “have often internalised the notion that others know best ... Are we to offer them the ultimate opportunity to give way to the will of those around them?” Or are we to demand that they bend to our will, instead?

Now, the predicted malign effects can happen, although, as Baroness Warnock pointed out, “being vulnerable is not a judgment that one ever makes about oneself. To be classified as vulnerable is to be regarded from a great height by lawyers or doctors, above all, or nurses.” But there are obviously things that society can do to mitigate such problems, if it chooses.

Consequently, as a matter of principle, none of these hypothetical possibilities can overcome the right of a suffering Sigmund Freud, who had thought more about life than a convocation of bishops or a dinner of lawyers, to ask a Max Schur — in effect — to kill him; or the right of his doctor and his daughter to be free from the risk of prosecution for having had the love to agree.

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