A passenger jet coming in to land at Heathrow airport had a near miss with a UFO, according to newly-released Ministry of Defence files.
One of the UFO sighting sketches in the newly-released files
The captain of the Alitalia airliner was so concerned he shouted "look out" to his co-pilot after seeing the brown missile-shaped object shoot past them overhead.
The mysterious incident near Lydd in Kent in 1991 was thoroughly investigated by the Civil Aviation Authority (CAA) and the military.
But having ruled out the object being a missile, weather balloon or space rocket, the MoD closed the inquiry and left the matter unsolved.
The unexplained close encounter is one of many recounted in military UFO documents made available online today by the National Archives.
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:: US Air Force pilot's account of being ordered to shoot down a UFO.
:: MoD request that Army and Navy helicopters should not take photos of crop circles.
:: Letter from a woman claiming to be an alien.
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The McDonnell Douglas MD80 aircraft was en route from Milan to Heathrow at 22,000ft with 57 people on board when pilot Achille Zaghetti saw the strange object 1,000ft above him.
He recounted: "At once I said, 'look out, look out,' to my co-pilot, who looked out and saw what I had seen.
"As soon as the object crossed us I asked to the ACC (area control centre) operator if he saw something on his screen and he answered 'I see an unknown target 10nm (nautical miles) behind you'."
A CAA document notes that Southern TV broadcast a story about a 14-year-old boy who reported seeing a missile flying at low level before climbing through the cloud and disappearing on the same evening.
An unnamed Whitehall official wrote: "It is our intention to treat this sighting like that of any other Unidentified Flying Object and therefore we will not be undertaking any further investigation."
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Is there life out there?
There were, however, a number of other similar incidents recorded the same year.
On June 17 1991 four passengers on board a Dan Air Boeing 737 saw a "wingless projectile" pass beneath the aircraft as it climbed from Gatwick Airport headed for Hamburg.
Then on July 15 the pilot of a Britannia Airways 737 reported seeing a "small black lozenge-shaped object" travelling at speed as they approached Gatwick.
Former US Air Force fighter pilot Milton Torres was convinced he had an encounter with an alien spaceship in the skies over England in the 1950s.
He was warned to keep quiet about the incident, but eventually talked about it 31 years later, the newly-released files show.
On the night of May 20 1957, Dr Torres, then aged 25, was on standby at RAF Manston in Kent when he received an urgent order to scramble.
He was told to intercept a UFO with "very unusual flight patterns" over East Anglia that ground radar operators had been tracking for some time.
It was so cloudy he could not see anything, but the object showed up clearly on his radar as similar in size to a B-52 bomber.
He was then ordered to fire a full salvo of 24 rockets at the object - something that came as a sobering shock to him.
But before he could carry out this instruction the UFO suddenly darted off and disappeared from his scope in a matter of seconds.
The next day a man claiming to be from the US National Security Agency threatened him with losing his flying status if he told anyone what happened.
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I think it was an alien spacecraft. It had a propulsion system that was beyond us - either magnetism or anti-gravity.
</blockquote><cite>Dr Torres, now 77 and living in Miami, Florida </cite>
The Ministry of Defence tried to stop military helicopter crews photographing crop circles for fear that this contradicted the official line that it had no interest in the phenomenon, the files show.
In 1991 the Centre for Crop Circle Studies wrote to the department highlighting cases where military aircraft had apparently hovered over fields where the elaborate patterns had appeared.
This concerned the MoD so much that it wrote to Army and Navy chiefs asking them to ensure this did not happen again.
One of the more eccentric letters sent to the department, dated March 1990, was from a woman claiming to be an alien.
She said her spaceship came down in Britain during the Second World War and was recovered by the military.
Another letter, dated January 1991, tells of an encounter with two aliens who landed their flying saucer next to a railway track near Warminster Army barracks in Wiltshire.