The trail of evidence begins with a note written in response to a request for information on UFOs made in 1976. From that note: "It is undesirable that even a hint of this should become public and we are currently consulting the [Air Historical Branch] on ways of expurgating the official records against the time when they qualify for disclosure [at the Public Records Office]." As the article details, this continued well into the 1990's. A final theory proposed in a 500-page report published last May called UFOs "indisputable," but attributed them mostly to weather conditions. Not surprisingly, the interest in UFOs throughout the 1970's and 1980's most likely had more to do with the Cold War than aliens.

-The Guardian: Is there anybody out there? How the men from the ministry hid the hunt for UFOs
-Ministry of Defense: UFO Reports 2002-2005