The National Archives is releasing the files because of numerous freedom of information requests seeking information about the government's UFO reports. Officials said that names of many individuals had been blacked out to protect their privacy and that the entire files had been reviewed to make sure their release did not compromise national security.

Ministry of Defense officials indicate in the files that UFO reports were only investigated to make sure no enemy aircraft had illegally entered British airspace. This was crucial during the Cold War when Russian planes posed a threat.

Officials said they did not try to solve UFO riddles once an enemy attack had been ruled out.

The vast majority of UFO reports come from members of the public who see strange things in the sky and jump to the conclusion that a UFO is involved even though there are logical explanations for what they observe, experts said.

"The most common things are aircraft lights, bright stars and planets, satellites, meteors, airships and things like that," said Nick Pope, another UFO expert who helped the Ministry of Defense investigate the phenomenon.

That was the case when a number of people leaving a Tunbridge Wells pub one night reported seeing a strange craft "with red and green" lights, according to the released documents.

Asked by police where the object seemed to be traveling, the pub crawlers said it appeared to be heading for London's Gatwick Airport. It didn't take a scientist to figure out it was a commercial plane making a routine approach.