The day was particularly appropriate. There was a great deal of publicity for the 50th anniversary of the world's first working modern computer, which ran at Manchester on 21 June 1948. And at 10.30pm the night before, 22 June 1998, the House of Commons had voted by a large majority to change the law so that homosexual and heterosexual acts would alike be governed by an 'age of consent' of 16. It was recognised by all sides that the issue at stake was that of equality. (Note added later: the law was indeed finally changed on 30 November 2000, despite intense opposition from christian leaders in the unelected House of Lords.)

I also alluded to another coincidence: that Sigmund Freud, as a refugee in 1938, stayed in the same building.

A coincidence I missed was that the day also marked the exact 50th anniversary of the foundation on 23 June 1948 of the pioneering Scandinavian gay movement which influenced Alan Turing in 1952 and gave him a liberating sense of the future.

There is more about Alan Turing's birthplace and on memorials to him on pages of my Alan Turing Internet Scrapbook.

This century has witnessed several revolutions in scientific thought and in technology. Relativity, quantum mechanics, antibiotics, genetics, aeroplanes, and television are some obvious examples. As the century draws to its close, however, it is another revolution that is now beginning to make the most profound mark on almost every aspect of our lives. This is the general-purpose computer. The central seminal figure in this computer revolution was Alan Turing, whose outstanding originality and vision was what made it possible, in work originating in the mid 1930s. Although it is now hard to see what the limits of the computer revolution might eventually be, it was Turing himself who pointed out to us the very existence of such theoretical limitations.

These issues raise pivotal philosophical questions, which will, I am sure, be argued about for centuries to come. Turing was, indeed, a deep and influential philosopher in addition to his having made contributions to mathematics, technology and code-breaking that profoundly contribute to our present-day well being.

The second is from the Rt. Hon. Chris Smith, MP, Minister of State for Culture, Media and Sport, who writes:

It is long overdue and very welcome indeed that the birthplace of Alan Turing should now receive official recognition. Alan Turing did more for his country and for the future of science than almost anyone. He was dishonourably persecuted during his life; today let us wipe that national shame clean by honouring him properly.

In 1952, while Nazi war criminals went free, Alan Turing faced punishment: a choice between prison and chemical castration. The shame is that this country enforced a sexual Apartheid law which penalised honesty. Betrayed by his country, Alan Turing embodied scornful resistance to that Apartheid; he acted and suffered accordingly.

Comment on his alleged naivete misses the only point that matters: that such a law should never have existed; least of all after a war fought in the name of freedom. But 1952 saw the first public opposition, and thereafter increased persecution induced a new consciousness. In the long term, the naive unrealistic intransigence of Alan Turing's attitude has eclipsed more worldly wisdom. After decades of non-violent struggle, last night the House of Commons voted to eradicate that law.

Alan Turing spoke the then unspeakable and showed no shame, although the hurt lay deep; and for that reason his suicide two years later fitted no stereotype of the defeated. He was a marathon runner, not given to giving up. But time has partly revealed his secret song of innocence and experience, and given significance to the veiled image of the poisoned apple. Being a free-thinking free-living and open homosexual could not, at the height of Cold War panic, be consistent with his chosen duty, of knowing innermost secrets of the security state. True, he ridiculed his surveillance by policemen he called 'the poor sweeties,' but it does not amaze me that eventually he found existence self-contradictory and life unliveable, on that tenth anniversary of the invasion made possible by his work.

Even the most independent mind can be robbed of will and purpose and meaning by friendly fire. But until that bitter end, he insisted on adventure both in personal and in scientific exploration: developing his futuristic non-linear biological theory as the world's first personal computer user at Manchester University. I wish I could unveil where his prolific last years would have led: to chaos theory, perhaps; to a nonlinear quantum mechanics, or cosmology. Instead, they were lost in a death that brought more stigma on himself and inflicted a wound on all around him.

There were wounds throughout Alan Turing's life; and many veils which can only be partially lifted. Beneath the irreverent wit of his famous paper of 1950 on the future of artificial intelligence, there is a serious anxiety over the relationship of thought and action, the individual and society. This reflects his own experience of life, and in particular his exclusion from the Manchester engineering culture, which respected only the outward and visible, valued the hard machine and not the soft. On Midsummer Day 1948, the world's first prototype general-purpose computer, the first Universal Turing Machine, was working at Manchester. The engineers had been supplied with the basic principle by the initiator of the project: Max Newman, Turing's close colleague both at Cambridge and at Bletchley Park. But this vital transmission of logical ideas goes unmentioned in the current celebrations of the brilliant engineering; and after fifty years Turing is still the Trotsky of the computer revolution. Turing had to bear another wound, in that he had been obliged to abandon his own visionary plan for the National Physical Laboratory, started so much earlier at the outbreak of peace in 1945.

But Turing never competed for the world's priority; it was not in his modest mathematical culture. Mathematicians had to be particularly quiet if they had worked behind the veil of Bletchley Park. Silenced by secrecy, Turing could never speak of having led British intelligence from defeatism to industrial-scale supremacy. In 1939, in Turing's words, no-one else was doing anything about the naval Enigma signals and so he could have the problem to himself. Alone, in naive unrealism, he broke the unbreakable; then, intransigent, saw it through into Allied mastery of the Atlantic by 1944. But he could not draw on this investment to execute his peacetime plan, the computer of the future.

At Bletchley Park, Alan Turing was captivated by his long-term dream of the computer. But Roger Penrose's message has hinted at a deeper level — his work beyond the limits of the computer. Max Newman's judgment also was that war took Turing away from his profoundest explorations, thinking the uncomputable. The decision that Turing took in 1938 lies behind another veil. I doubt whether Sigmund Freud, by coincidence exiled here in Turing's birthplace in that year of refugees, could have analysed how Turing chose to bite Snow White's apple, and forgo the paradise of pure mathematics. That decision is too deeply embedded in the complex bonds between the unique individuality of genius, and our common planetary home. In the perspective of centuries, to which Roger Penrose has alluded, Turing's decision may seem a sacrifice of the truly long-term: losing the marathon of mathematics, for a sprint to save a self-destructive world.

Even that great original work, the computable numbers of 1936, from which the computer was to flower ten years later, had its wounding aspects: King's College, Cambridge, that oasis of sexual tolerance, had become his home; but that University gave him scant recognition. And that work also emerged from behind a veil covering the deepest pain, where love and sexuality and free-ranging intellect were inseparable: the death of Christopher Morcom in 1930. The nature of spirit, as Alan Turing described it to Mrs Morcom, always remained a natural wonder barely compatible with the orthodox academic and scientific world.

School and family held special buried trauma too; but lastly — or firstly — my backwards arrow of time points to our common natural mystery of birth: the mystery of how matter comes to support human mind, which was the burning theme of his lifelong enquiry. On that subject the veil of nature as yet remains in place, but his work has given a foundation for a new century of natural philosophy.

No more war, please.

It is the greatest honour to unveil the place where Ethel Sara gave birth on 23 June 1912. My sentiments are not the same as those that impelled her to rediscover her dead son and tell her story. But I hope she would recognise an echo of her language when I conclude: The law killed but the spirit gives life.

Andrew Hodges, 23 June 1998.