Reports of "flying Toblerones" and objects travelling at 1,100 mph across the Scottish sky have been released by the Ministry of Defence.
The files detail how unidentified objects have been witnessed flying over a range of locations across Scotland.
Among them were one from a senior air traffic controller at Prestwick Airport who reported seeing a fast-moving UFO on the airport radar.
While four fishermen spotted a flat, shiny object hovering off the coast.
The Scottish accounts are among the thousands of reports made of close encounters with UFOs across the UK which have been released in a joint project between the MoD and the National Archives.
The Prestwick airport incident in February 1999 led to an extensive investigation by RAF air defence staff who impounded radar tapes from a number of airports around the UK.
But the report concluded that no additional evidence could be found to corroborate what the air traffic controller had spotted.
In another file, a report reveals four members of the crew of a fishing trawler in the North Sea spotted a flat, shiny, round object hovering 19 miles north-east of Fraserburgh on 18 August 1997.
They tracked the mysterious UFO on their surface radar for several seconds before it vanished.
Also included in the previously top secret files is the testimony of a West Lothian electrician who spotted a "Toblerone-shaped" UFO hovering over a field.
A sketch of the craft is included in the report.
Other document describe a request submitted to former Prime Minister Tony Blair from a councillor for an inquiry into 600 alleged sightings in the so-called Bonnybridge Triangle, near Falkirk.
The area is renowned among enthusiasts as being among the best places in the world to see UFOs.
In October 1997, Bonnybridge councillor Billy Buchanan, of Falkirk District Council, wrote to Mr Blair demanding the phenomena were investigated after five years of pursuing the matter.
He wrote: "For five years the people both you and I represent have witnessed a phenomenon in the area that has been left unexplained.
"I wrote to your predecessor John Major, I have also contacted our local MP Dennis Canavan who put me in contact with the MoD who told me quite strongly that nothing was happening in Bonnybridge that was a threat to national security."
He continued: "I have tried to get an answer for the people and have been ridiculed for it.
"I appeal to you Mr Blair to get the phenomenon investigated."
An MoD response to the letter said there were no grounds to investigate the matter.
But Mr Buchanan did not give up and wrote to Mr Blair once again in 1998 demanding "the truth".
Experts believe the records highlight how shapes of reported UFOs have changed over the last few decades, possibly explained by representations of UFOs in popular culture.
Many reports in this latest file describe aircraft as big, black and triangular in shape with lights along the edges, whereas the predominant form in the 1940s to 1950s was saucer or disc-shaped.
Stuart Campbell, the Edinburgh-based author of the book The UFO Mystery Solved, said: "UFO reports have all sorts of explanations - lights in the sky from aircraft to hot air balloons.
"Every mystery has a solution somewhere, everything has a rational explanation. The alternative is that we don't live in a rational universe.
"The job is to find an explanation and that can be hard work sometimes."
The released files are available to download for free for a month from the National Archives website.