If you want to uncover the DNA of an Olympic hero, get on the M4, turn off at Swindon, drive through the delightful town of Marlborough and take a right up a gravel track until you arrive at a rambling farmhouse. Inside you will find the tall, lithe and unmistakably Corinthian figure of David Hemery, a man who might have been plucked from the imaginings of Pierre de Coubertin.

Forty years ago, Hemery took 48.12 seconds to win gold and shatter the world record in the 400 metres hurdles at the Mexico City Olympics, his velvety progression to the line enhanced by a spectacularly energetic performance in the commentary box by David Coleman. In the four decades since, Hemery has stood, immovable, as sport has been buffeted by scandal, his implacable belief in the values of fair play, self-fulfilment and comradeship all the more striking given that they have been consistently betrayed by the Olympic movement.

“I am as passionate about sport as ever,” he says, eyes sparkling. “It is not about winning at all costs but about fulfilling one's potential. When I lined up I was never thinking about getting one over on my opponents - I was concerned with bettering myself as an athlete and as a human being. That is the essence of sport.” One is tempted to say that in Hemery the founding idealism of the Olympic movement finds its truest expression - in his undimmed passion for sport (he runs daily); in his conviction that sport can make for a more enlightened world; above all, in his moral seriousness. I ask whether it would be legitimate for athletes to use next month's Games to put pressure on China, whether over Sudan, Tibet or human rights.

“I think that British athletes should have absolute freedom of speech in Beijing and that there should not be any gagging orders at all,” he says. “But I also think that protests are at their most effective when they draw attention to something with which the athlete is personally involved with. Take the Black Power salutes in 1968. They were very dignified: they just put their fists up and said, ‘Look at us.'

“I had lived in the United States for some time and I knew that they were heroes when they were on the podium because they were winning for America. But I also knew that, when they got home, they would struggle to get mortgages and jobs. They were right to draw the world's attention to that lack of consistency; to that injustice. I am a pretty level-headed person but injustice is the one thing that really riles me up.” Hemery is a throwback to a bygone age, a world of chivalry and duty. The world is not going to hell in a handcart - we are more ethically enlightened than ever - but Hemery is an essential reminder of some of the ways in which our culture, not least our sporting culture, has lost its way. His sorrow regarding the slow strangulation of his beloved athletics by the spectre of doping is deep indeed.

“How desperately sad to have a sport where we do not know who is clean,” he says. “It is something that affects all of us, including me. But I valued the fact that Paula Radcliffe said: 'I want people to take my blood now so that whenever any test is developed in the future they can find out whether I was on anything.' I find it heartening that there are some people who are prepared to try to get there through hard work.”

When it comes to life bans for drug taking, Hemery's belief in forgiveness battles hard with his passion for clean sport. “I was not in favour until quite recently,” he says. “I used to think that everyone should be given a second chance, but then someone pointed out that a lifetime ban does not mean that we cannot welcome them back into society. It is simply a ban from athletics in the same way that a drunken pilot is never allowed to fly again.

"The BOA's stand on this was not made by the suits, it was made by the athletes. Much as it is hugely regrettable that Dwain [Chambers] has become an exposed figure, it is not personal. It is the athletes saying that they would absolutely prefer a team which, to the best of their knowledge, is clean. I welcome that and it wouldn't surprise me if other countries join our stand. We are the ones saying, ‘Let's try and clean this up.'”

Since his retirement from athletics, Hemery has taught economics, coached, written books and served as president of UK Athletics. He now combines running management training courses and his vice-chairmanship of the British Olympic Association with a continuing engagement in man's moral struggle.

“I have a great belief that the world is moving in the right direction,” he says. “We get worried about things like knife crime, and, of course, it is a tragedy for those afflicted. But we forget that it is a tiny minority.

“Someone said to me recently that she really lives in fear. I said to her, 'Think, instead, about the vast number of people who live in peace.' ”