© UnknownDefence experts examined a 2004 photo of a "flying saucer" over Retford town hall
The Ministry of Defence files released by the National Archives cover reported sightings of UFOs from 1985 to 2007.
In one, a military officer predicts embarassment if the public discovered a "lack of funds and higher priorities" were stopping UFO investigations.
The 34 files include sightings of lights over Glastonbury and a "flying saucer" in Nottinghamshire.
They can be downloaded free of charge for a month from the National Archives website.
National Archives consultant Dr David Clarke said it was about time the data was released.
"One of the most interesting documents in the files is a piece from an intelligence officer, who basically says that despite thousands of reports that they've received since the Second World War, they've never done any study or spent any money or time on the subject, and they say that people just won't believe that when they find out."
The internal memo from a DI55 [defence intelligence] wing commander dated 5 July 1995 says the media's portrayal of DI55 as a "defender of the Earth against the alien menace" is "light years from the truth."
The file shows the officer feared that if intelligence's interest in UFOs was to be revealed it could cause "disbelief and embarrassment since few people will believe the truth that lack of funds and higher priorities have prevented any study of the thousands of reports received."
A former Ministry of Defence UFO investigator said the files reflected debate over the significance of reported UFO sightings.
Nick Pope worked at the MoD between 1991 and 1994.
He said the files were quite revealing: "The fascinating thing about these files is that they show that just as in society there's this huge debate about UFOs - is it really interesting, are we being visited by aliens - or is it all just nonsense?
"We were having the same debates in the Ministry of Defence. Some people thought it was a waste of time and money, others thought it was of extreme defence significance."
Reported sightings
The files show Alex Birch contacted the Ministry of Defence after capturing a series of images of what looked like a "flying saucer" over the town hall in Retford, Nottinghamshire.
In July 2004, the ministry sent the images to the Defence Geographic and Imagery Intelligence Agency (DGIA).
The agency's report said "no definitive conclusions" could be made from the photos. But it added: "It may be coincidental that the illuminated plane of the object passes through the centre of the frame, indicating a possible lens anomaly, eg a droplet of moisture."
The files include 2001 testimony from a retired RAF fighter controller and an MoD official on a 1956 UFO incident in Suffolk.
Ex-controller Freddie Wimbledon describes scrambling fighter planes to intercept a UFO seen on radar and by people on the ground at RAF Lakenheath. He says it reportedly latched on to a fighter plane, "following its every move" before departing at "terrific speed".
Retired MoD official Ralph Noyes describes being shown footage of UFOs taken from the aircraft.
'Wriggling around in the sky'
Another file describes a 2003 sighting by a mother and daughter of "worm-shaped" UFOs "wriggling around in the sky" over East Dulwich in south-east London.
In their testimony to the MoD, two men in "space suits and dark glasses who called themselves Mork and Mindy" joined police officers who attended the scene.
A letter from the woman later complained they had been fed "a lot of rubbish, presumably to make us look foolish and our story unbelievable".
Police told the MoD the officers could not see anything in the sky and "concluded it was possibly a reflection of a star and a street light in her window".
Experts had concluded that sightings of lights in the sky in the summer of 2006 were likely to be Chinese lanterns, an additional file shows.
The UK military and intelligence agencies inability to investigate the countries UFO sightings is either a ruse or a sign that they're mostly useless. I'm leaning toward the former explanation, but the latter one is also attractive.
It's a wonder that the UK has managed to survive for so long, since it's such a dysfunctional society. The persistence of ridiculous class and regional distinctions, all of its sullen animosities and casual daily oppression mixed with nightly bits of equally casual violence in and around the pubs and clubs can only make the observer shake their head and be happy not to live in the UK.
The ludicrous neo-feudal class structure of UK society ensures that it is not a meritocracy in politics, finance and industry, for the most part, but is mostly led by a cadre of pampered inbred morons who have no clue about what their objectives should be or how to go about leading.
Beneath them is a rather larger cohort of managerial types who are not quite so well ancestored or privileged and have some idea about what might done but refuse to insist upon it for fear of their jobs and also because they resent the hell out of the fact that they'll never get a chance to join the upper ranks, no matter how competent they are.
And under them are all the day to day working people who might be well educated, or not, but have learned to just tug their forelocks and do the minimal required because they're not appreciated as anything other than cogs in the system and can never hope to get promoted.
It's actually rather amazing that those large islands filled with lots of people who mostly resent each other and hate most politicians with admirably equitable disdain haven't blown up into insurrection before.