Forty years ago, in April 1945, the allied advance into Germany took me from Hanover through Celle toward Hamburg and Lubeck. My unit had discovered a particularly interesting intelligence target in Celle -- a laboratory for separating isotopes of uranium. Having dealt with it, we were anxious to move on quickly. Our route led us past the villages of Bergen and Belsen.

We knew vaguely of a large camp in this area but had failed to receive either the order to keep clear of it or the information that the camp was a concentration camp and that its population was suffering epidemics of typhus, smallpox and other diseases.

My first view of the Bergen-Belsen camp was of a high barbed-wire fence at a corner in the road with what appeared, from a distance, to be logs stacked inside it. On closer view the logs turned out to be neatly stacked corpses, of which there were some 10,000 unburied in the camp. From the main gate the prospect was indescribable, a desolate litter of human beings, Jewish, French, Austrian, Polish, Czech, gypsies, Dutch and Belgian, mostly dehumanised to a point just short of death. Many were in fact dying, and there were corpses as far as the eye could see. It was the first warm day of the year, and some inmates had removed their striped concentration camp uniforms and become skeletons ambling and staggering in the spring sunshine. Inside the huts the scene was even more brutal -- every bunk crowded, the living, the dying and the dead intermingled. The huts gave a horrible meaning to the word "concentration."

We were totally unprepared for Belsen. I had probably been better educated than most about Hitler's anti-Semitism, because my mother and my aunts, from 1930 on, had been deeply outraged by it and had looked after many refugees. But Belsen gave a new and monstrously physical dimension to Hitler's racist obsessions. We were stunned and in shock. Nothing in our five years' experience of war bore any relation to this terrible and mindless enormity. In the hour of victory a great cloud obscured the sun. Our rage was compounded by a feeling of absolute helplessness in the face of such fathomless misery and evil. We could only await the arrival of more troops and, above all, medical personnel.

The physical desolation was appalling, but what moved us most in the long run was, I believe, the spectacle of deliberate human degradation on a vast scale. To this day I wonder what can have been the state of mind of those who executed so faithfully this crazy and bestial program. What can they have thought of as they fell asleep at night? How could any lunatic ideology or grudge against humanity justify their actions or deaden their feelings? And yet, to them, working at Belsen must just have been their routine daily job.

It is not possible to come to terms with such a phenomenon, let alone to forget it. We should not try to do so. Rather we should remember how far the human spirit can be twisted by organized bigotry, hatred and racism, and resolve to see that nothing remotely similar can happen again.

Certainly the mass murder of the Holocaust and the horror of the concentration camps were powerful incentives for international efforts such as the Universal Declaration of Human Rights and the Genocide Convention. We are, perhaps, more on guard now and less tolerant of the casual bigotry and prejudice which, in the hands of a skilled demagogue, can be shaped and concentrated to bring about such a nightmare. But genocide can, and does, still happen. Since 1945 there have been several cases, some on a vast scale.

There is a natural human tendency to forget, to remain ignorant or to deny responsibility. It is, supposedly, a comforting tendency, but there are times when it plays directly into the hands of criminal or racist lunatics. We must remember and forever be on guard. That is the message of this 40th anniversary.