Previously classified documents reveal the UFO phenomenon was discussed at the highest level of government worldwide.
In December 1977, the Government used its influence to talk down a call by Grenada president Sir Eric Gairy for a UN agency to conduct research into alien sightings.
About a year later, the House of Lords held a debate on the subject of UFOs, the files show.
One of the documents describes a "War of the Worlds" incident in 1967 that was treated as a potentially real alien invasion of the UK.
The RAF was flooded with calls from the public reporting six small "flying saucers" discovered in locations in a perfect line across southern England.
Four police forces, bomb disposal units, the army and the Ministry of Defence's intelligence branch were all mobilised.
But it later emerged the saucers were a 'rag-day' hoax by engineering students from Farnborough Technical College.
Another file tells of a family capturing on film flashing red and white lights zig-zagging their way through the sky in 2003.
Police officers, including a helicopter team, also witnessed the 20 to 30 lights over Bromley, Kent, and reported the incident. Radar checks revealed nothing unusual.The documents read: "A policeman sent to investigate confirmed the sighting. Objects were moving faster than any man-made aircraft."
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