The government took the threat of UFOs so seriously in the 1950s that UK intelligence chiefs met to discuss the issue, newly-released files show.
Ministers even went on to commission weekly reports on UFO sightings from a committee of intelligence experts.
The papers also include a wartime account claiming prime minister Winston Churchill ordered a UFO sighting be kept secret to prevent "mass panic".
It is claimed, the prime minister was so concerned about a reported encounter between a UFO and RAF bombers, that he ordered it be kept secret for at least 50 years to prevent "mass panic".
Nick Pope, who used to investigate UFO sightings for the MoD, said: "The interesting thing is that most of the UFO files from that period have been destroyed.
"But what happened is that a scientist whose grandfather was one of his [Churchill's] bodyguards, said look, Churchill and Eisenhower got together to cover up this phenomenal UFO sighting, that was witnessed by an RAF crew on their way back from a bombing raid.
This event should be immediately classified since it would create mass panic amongst the general population and destroy one's belief in the church.
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