Sketch of a UFO spotted in Hemsworth, West Yorkshire, on 25 March 1988
The Ministry of Defence has closed its UFO unit after more than 50 years of investigating reported UK sightings.
A hotline and e-mail address for the public to report possible sightings was shut on 1 December because it had no "defence value", the MoD said.
The officer handling reports has moved to another post, saving £44,000 a year.
The MoD said the unit had received thousands of reports, although none had yielded proof of aliens or any security threat to the UK.
In a statement, the MoD said it had "no opinion on the existence or otherwise of extra-terrestrial life".
It went on: "In over 50 years, no UFO report has revealed any evidence of a potential threat to the United Kingdom.
"The MoD has no specific capability for identifying the nature of such sightings. There is no defence benefit in such investigation and it would be an inappropriate use of defence resources."
An MoD spokesman added that resources were being "focused on the top priority - the front line in Afghanistan".
He added: "Any legitimate threat to the UK's airspace will be spotted by our 24/7 radar checks and dealt with by RAF fighter aircraft."