Photographs taken of a UFO hovering next to an RAF jet over Scotland were treated very seriously by military investigators, newly-released Ministry of Defence files show. Skip related content
Witnesses saw the mysterious large diamond-shaped object hanging in the air for about 10 minutes before it ascended vertically at high speed.
Military experts concluded the aircraft was a Harrier, but could not identify the UFO despite apparently commissioning detailed line drawings of it.
Fearing there could be significant media interest, the MoD took the unusual step of briefing ministers about the sighting.
The incident also discloses that British military intelligence officers tasked with investigating UFO reports took a close interest in claims the US was developing a top secret spy-plane.
The sighting is included in military UFO documents made available online by the National Archives.
The seven files, produced by the DI55 branch of the Defence Intelligence Staff, relate to the period between November 1987 and April 1993 and contain details of around 1,200 separate UFO sightings.
They demonstrate that British officials were more concerned about advanced new aircraft being developed by the Russians and Americans than little green men.
The files include numerous cuttings from magazines and newspapers relating to rumours that the US military was developing a hypersonic spy-plane known as Aurora.
Attached to one article about Aurora from September 1991 was a note from an MoD official that read: "Attention is really focusing on this now, notwithstanding a recent USAF 'denial briefing'"
Newly released UFO files - March 2009: http://ufos.nationalarchives.gov.uk/