Sussex Police have investigated hundreds of reports of UFOs since 2007, The Argus can reveal.
Over the past six years, 111 reports of unidentified flying objects over Sussex have been reported to the force and officers have treated them “seriously”, a spokesman told the newspaper.
He said he could not estimate how much this had cost Sussex Police.
He added: “We always take calls seriously, but in the case of reports of UFO sightings none have ever been substantiated.
“In recent years, the increase in the popularity of Chinese lanterns has brought about the odd report and there will occasionally be calls as a result of a celestial occurrence or falling space debris.”
He said celestial occurrences usually meant meteorites and other space activity.
So far in 2013, only one person has contacted Sussex Police to complain about UFOs.
But in 2010, 31 people complained of UFOs and a year earlier 35 people complained.
The Ministry of Defence has a list of UFO sightings in Sussex.
Documents released by the National Archives include the case of an airline pilot in Hellingly, near Hailsham, who reported an object the size of a large eagle flying past his house.
The man reported the sighting in July 2001, saying he was in the garden with his son when he saw an object made of three joined circles fly past.
He reported the incident to the police and claimed he watched the fast-moving UFO for five minutes.
In September of the same year a woman was driving along a road in Hailsham when she saw something overhead.
The report of the incident said: “She saw a very large, round object, followed by another object, green and conical in shape.
“Both were travelling very fast in parallel with her car.”