Prime Minister Tony Blair was briefed on the UK's files about UFO sightings in 1998, newly declassified MoD documents have revealed.
Writer Dr David Clarke had urged him to "consider making available for public scrutiny all of the many and varied UFO reports compiled by the government".
The request came as the government began to implement Freedom of Information (FOI requests).
Some 6,700 pages of UFO documents have been released by the National Archives.
The documents also include details of a briefing made before a House of Lords debate on UFOs in 1979, and reveal that former prime minister John Major had been asked by a fellow MP in 1996 whether the government would set up a national inquiry into UFO sightings.
The declassified documents - from the MoD unit which investigated UFO claims from 1950 until it was shut down in 2009 - also include several sightings and investigations.