A former chief of defence staff warned Margaret Thatcher's government in 1985 that its "perfunctory" dismissal of UFO sightings near an RAF base shared with the US Air Force in Suffolk could turn into a political "banana-skin" because it was unexplained.
In a letter to Michael Heseltine, Mrs Thatcher's defence secretary at the time, the late Lord Hill-Norton said the sightings of unidentified flying objects in Rendelsham Forest by USAF personnel in December 1980 had "puzzling and disquieting" features that have never been satisfactorily explained.
The letter, written on 1 May 1985 is among official government documents on UFOs released today by the Ministry of Defence to the National Archives. Fourteen files containing more than 4,000 pages spanning 15 years between 1981 and 1996 have been placed online.
Lord Hill-Norton's letter covers perhaps the best-known British UFO incident of the period when the USAF twice reported mysterious lights and a metallic flying object in the woods at the perimeter of the base. They said a triangular-shaped object had left radiation traces and three visible markings in the ground.
Colonel Charles Halt, the USAF deputy base commander, who saw the lights himself, wrote a short report on 13 January 1981, but the Ministry of Defence denied all knowledge of the events until the colonel's memorandum was released in June 1983 under the US Freedom of Information Act. The MoD's public response was that the incident had no defence interest.
"My personal view, having considered the fragmentary but compelling evidence brought to public knowledge by the media, is that the case cannot be disposed of in these rather perfunctory terms," Lord Hill-Norton wrote. "If the report made by the USAF authorities in January 1981 is accurate, there is evidence that British airspace and territory are vulnerable to unwarranted intrusion to a disturbing degree.
"If, on the other hand, the report of the deputy base commander must be dismissed ... then we have evidence – no less disturbing, I suggest – that a sizeable number of USAF personnel at an important base in British territory are capable of serious misperception, the consequences of which might be grave in military terms."
The MoD reply repeateded that if there were sightings of unidentified flying objects they did not have any defence significance. A "final position statement" was prepared in 1985 by officials for the defence minister, Lord David Trefgarne. "It is highly unlikely that any violation of UK airspace would be heralded by such a display of lights," the file continues. "I think it equally unlikely that any reconnaissance or spying activity would be announced in this way.".
Other MoD documents released relate a UFO incident in Belgium in 1989 and 1990 when Belgian Air Force F-16 fighters were scrambled to intercept strange, brightly-lit, triangular-shaped flying objects reported by police and others. A statement sent to the MoD in November 1993 by General Wilfried de Brouwer, chief of operations in the Belgian Air Staff, confirmed that the fighters had locked-on to something with their radar but were unable to explain what it was.
The MoD said there had been no threat to the UK and that it has never detected a "structured craft flying in UK airspace that has remained unidentified".
One report in the MoD file details a supposed encounter by two Staffordshire teenagers who rushed into a police station late on 4 May 1995 claiming that they had been stopped in a field by aliens with lemon-shaped heads who told them, "We want you; come with us", then vanished in a glowing-red saucer.
'X-Files' blamed for rise in sightings
This is the fourth instalment of files on UFOs being released by the Ministry of Defence to the National Archives and they include details of a wide variety of "sightings" that may owe more to Mulder and Scully, above, than little green men.
The files contain UFO reports of 800 sightings between January 1993 and August 1996, but in 1996 alone 609 incidents were logged, three times more than all the previous three years together.
"The large increase in numbers during 1996 may reflect increased public awareness of UFOs and aliens due to the popularity of the TV series The X Files and the release of the movie Independence Day," said David Clarke of Sheffield Hallam University, a consultant to the National Archives on the MoD's UFO files.
Some of the sightings had a rational explanation, such as the reports of a brightly illuminated oval object moving slowly over London during 1993 and 1994. It was actually a Virgin airship advertising the launch of the Ford Mondeo which as seen even by the MoD's UFO desk officer. Another explicable sighting was early on 31 March 1993 by police and military personnel from RAF Cosford near Wolverhampton. More than 30 sightings of fast-moving bright lights were reported but they were caused by the re-entry into the Earth's atmosphere of the Russian Cosmos 2238 satellite.
And two youths reported a UFO landing in a field at Chasetown in Staffordshire. They told police they were hit by a blast of heat, and a face appeared with a voice saying, "We want you; come with us." They panicked and fled.
Cheshire police reported an apparent alien attack in a cemetery which left a smouldering railway sleeper with a hole burned through it. Bonnybridge in southern Scotland became a hotspot for UFO sightings in the mid-1990s with 3,000 reports of mystery objects in the sky. A Bonnybridge councillor tried to get the town twinned with Roswell, the New Mexico town were some people believe an alien spacecraft crashed in 1947, a craft dismissed by the US military as a high-altitude surveillance balloon.