Britain's National Archives has released 1,500 pages of documents pertaining to UFO sightings in the country between 1986 and 1992.
The 19 files, which were posted on the archives' website Monday, largely debunk a host of UFO sightings but many also remain unexplained.
It is the second batch of UFO files that Britain's military has put out this year.
David Clarke, a UFO expert who has worked with the National Archives, said a total of 160 UFO-related files are expected to be made available to the public over the next few years.
Alien abduction recollections, sketches of the spotted crafts and alleged aliens along with newspaper clippings and government and military documents are included in the detailed files.
Some details, including the names of witnesses, are blacked out in the documents but the public is largely allowed to browse through the pages and pages of information in the reports.
In one file, a correspondent tells the military he was shouted at by aliens while sleeping outdoors.
Another writes in "with extraordinary news," saying the "legendary 'feathered serpents"' are waiting for permission to land on Earth.
‘ If you were an space traveller, would you waste your time coming to this planet. Imagine how horrified Aliens would be if they came and saw how we treat each other, the world and it's creatures.’
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In another, an American pilot alleges he was ordered to shoot down a UFO over eastern England. The statement was forwarded to the Ministry of Defence by a UFO enthusiast and was kept on file though the military turned up no evidence of it in its official records.
UFOs spotted by pilots
More disturbing was a sighting in 1991 by crew aboard a Gatwick-bound Britannia Airways Boeing 737, who saw a "small black lozenge-shaped object" zipping past about 90 metres to the left of the aircraft.
The airport confirmed seeing an object on its radar and clocked it travelling at 190 kilometres per hour. Air traffic controllers quickly warned the next aircraft to turn out of the object's flight path, although by then the object had disappeared from view.
Speculation centred on a weather balloon released in the area the same day, but an investigation could not determine what the UFO was.
Among the newly released documents, there is also an investigation that was conducted after Alitalia pilot Achille Zaghetti spotted what he thought was a missile.
Zaghetti's jet from Milan was arriving at London's Heathrow Airport on the evening of April 21, 1991, when a flying object streaked across his field of vision.
"At once I said, 'look out, look out,' to my co-pilot, who looked out and saw what I had seen," Zaghetti wrote in his report.
"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 10 nautical miles behind you."'
An investigation later ruled out a missile — but it never provided further explanation.
In another one of the files, four passengers on a Hamburg, Germany-bound Dan Air 737 on June 17, 1991, spotted "a wingless projectile pass below and to the left of the aircraft" as the flight climbed out of London's Gatwick Airport.
"It would seem to have passed fairly close by as the passengers were able to see it quite clearly," the Civil Aviation Authority wrote.
The newly released records also reveal officials did get to the bottom of many of the sightings.
While some sightings are revealed to be satellites, meteors or weather balloons, some alleged close encounters have more unique explanations.
On a clear November afternoon in 1992, an office worker called the Ministry of Defence, to report a strange, shimmering object was descending slowly over London's Regent's Park.
"As call progressed, it became clear that the object was a kite," an unidentified military official noted in his report.
Another report documents that light shimmering off the wings of seagulls was put forward as an explanation for UFOs that were spotted in Essex in August 1992.
What turned out to be a laser light show at a Tina Turner concert in London is 1989 is also revealed in the documents to have been called in as a potential close encounter.