I was once shown around Munich’s Olympic Stadium by a suave character who worked for the city council. He had silver hair, a permanent smile, drove a beautiful BMW and was generally a born public relations man. Then we found the stone tablet commemorating the Israeli athletes massacred by Palestinian terrorists at the 1972 Olympic Games.

When I remarked in surprise that the tablet had been unveiled only in 1995, my guide’s poise crumbled. For several minutes he stammered. He was so ashamed that the horror had happened in his city, that it was not commemorated for 23 years, and that he had to explain this to a foreigner.

That tablet now is the 1972 Olympics, the sole salient memory of the games. Only the medal-winners and their mothers care who won which event. The worry is that one day some tablet somewhere in London will be all that remains of the 2012 Olympics.

Though Munich is the only well-known terrorist attack on a sports event, there have been many others. Louis Mizell, a former special agent and intelligence officer with the US State Department, has logged 171 such attacks in sport since 1972.

The history goes back at least to a British act of terrorism in Dublin on November 21, in 1920, the original “Bloody Sunday”. That morning the IRA Irish Republican Army had assassinated 14 British intelligence officers. In the afternoon the “Auxiliaries”, a force of former British officers, opened fire at a Gaelic football match at Croke Park. Fourteen people died, including two footballers. and a Wexford man who was whispering the act of contrition into a dying player’s ear.

Some terrorism occurred in the following decades, but it was Munich that changed the sporting climate. Thanks to recent improvements in satellite technology, the Palestinian kidnappers were seen live by hundreds of millions of people. Terrorists everywhere realised that sport could bring them a global audience.

It has been mayhem since. When anti-Castro murderers blew up exploded an aircraft carrying the Cuban fencing team in 1976, they may not have been thinking chiefly about sport, but later terrorists were. Many atrocities are hardly remembered today: the 20 Philippine soldiers killed in a race in 1987, after terrorists posing as volunteers handed them poisoned water; the 27 basketball players and spectators killed in the same country when terrorists threw hand grenades on to the court in 1989; the Canadian killed by a booby-trapped softball bat in Chile a year later. Perhaps the worst atrocity was North Korea’s explosion of a South Korean airliner in 1987, which killed all 115 passengers. “The whole plan was to destabilise the 1988 Olympics in Seoul,” says Mizell. who worked on the case.

And then there was the big one that did not happen. A fortnight before the football World Cup in France in 1998, European police rolled up foiled a plot against it, arresting about 100 people in seven countries. Terrorism was then widely considered a yawn, and the episode was soon forgotten. However, It is detailed in the curiously ignored book Terror on the Pitch by Adam Robinson. the pen-name of a journalist based in the Middle East). Quoting letters detailing the plot sent by members of the Algerian Armed Islamic Group, Robinson says they meant to strike at the England-Tunisia game on June 15 1998.

Backed by the former goalkeeper Osama bin Laden, the terrorists planned to infiltrate the Marseilles stadium, shoot some England players blow up others, and throw grenades into the stands. Their colleagues were then to burst into the US team’s hotel and murder players. Others would crash an aircraft into the nuclear power station near Poitiers. in France, causing meltdown. It would have been a European September 11, only worse.

It is possible to dismiss these letters as a terrorist wish-list, but we now know these people are not dreamers. Another bin Laden biographer, Yossef Bodansky, says one reason that al-Qaeda bombed the American embassies in Kenya and Tanzania in August 1998, killing 224 people, was “the failure of the primary operation, an attack on the soccer World Cup”. Incidentally, the chief plotter against the World Cup, Omar Saiki, spent three years in jail and then requested political asylum in Britain.

If terrorism can ruin sporting events, security can at least spoil them. People complained of hysterical overpolicing at the Montreal Olympics of 1976, when there were 16,000 security personnel. Well, in Athens last year there were 45,000. London may have more.

 Mizell denies that security will spoil the Olympics. “The British have too much experience, probably more than any police force in the world. They are the ultimate gentlemen cops.” And besides, people are used to security now.”

But he fears another atrocity. “The terrorists have unlimited targets at an event such as this, including stadiums, buses, airports, hotels. They’re operating in a crowded, chaotic environment that’s perfectly conducive to deception. We keep thinking about al-Qaeda, but there are hundreds of terrorist groups around the world. Each country is represented at the games, and each country has different enemies.”

In the decade After Munich, people debated whether the Olympics could survive. The question remains valid. The “games” are now an armed camp where sponsors’ guests queue to see sometimes doped-up athletes compete in disciplines that nobody normally bothers watching. The fear is that Wednesday’s celebrations in Trafalgar Square were the high point of the 2012 Olympics.