Geoff Sommer, of the Rand Corporation in Santa Monica, California, said that governments would be wrong to warn of an impending impact that could destroy all life if there was no realistic prospect of stopping it. The panic, misery and disruption that such a warning would cause would not be worthwhile, he told the association.

It would be better for the fewest people to know that mankind was about to become extinct in a fashion similar to the dinosaurs. Mr Sommer said: “It makes sense to warn if there’s something you can do but if you can’t intercept it, if you can’t move people out of its way, it makes sense not to occasion further social costs.”

His view was strongly disputed by Lee Clarke, Professor of Sociology at Rutgers University, who said people had a right to be told about the impending end of the world. “If we see a monster event coming, an extinction event, common sense would tell me I want to know and that it’s not up to him, or up to some high-level bureaucracy, to decide whether I know or not,” he said.

“The reaction might not be what most people expect. Look at people on death row, people in prison camps during the Holocaust, people with terminal cancer,” he said. “You might want to make peace with your God, for example.”

The world would have two main options if astronomers detected a large asteroid or comet on a collision course, scientists said. If the object were less than a kilometre in diameter, it should be possible to calculate the precise spot it would hit and evacuate the area.

Impact by a body ten times larger, such as the asteroid generally thought to have wiped out the dinosaurs 65 million years ago, would give the human race little chance of surviving. Mankind would have to try to deflect it or blow it up.

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