The Ministry of Defence will destroy all future UFO reports it receives so it does not have to make them public, a previously secret memo reveals.
Britain's official UFO investigation unit and hotline were closed down at the start of December.
Since then reports of strange sights in the skies sent to the MoD have been kept for 30 days before being thrown out, the newly released policy document shows.
This stance was adopted so defence officials would not have to publish the information in response to freedom of information (FoI) requests or pass it to the National Archives.
The memo, dated November 11, 2009, sets out the MoD's reasons for shutting its UFO unit and ceasing to invite the public to send in details of sightings.
It notes that the number of reports the department received soared last year, taking up extra resources and diverting staff from "more valuable" defence-related activities.
The MoD recorded 634 UFO sightings in 2009, the second highest annual total after 1978, when there were 750, according to UFO expert Dr David Clarke.
This compares with an average of about 150 reports a year over the past decade.
The memo states: "The dedicated UFO hotline answer phone service and e-mail address serve no defence purpose, and merely encourage the generation of correspondence of no defence value.
"Accordingly these facilities should be withdrawn as soon as possible."