Nick Pope, who investigated the strange phenomena for the Ministry of Defence, compared the believers to the X-Files series character Fox Mulder.
The famous fictional FBI agent, portrayed by David Duchovny, investigated alleged paranormal mysteries alongside his sceptical colleague doctor Dana Scully, played by Gillian Anderson.
The US government has acknowledged a top-secret project at the Pentagon – called the Advanced Aerospace Threat Identification Program (AATIP) – ran for four years officially from 2008.
Top officials working alongside scientists from Bigelow Aerospace examined videos of UFOs, and reportedly studied debris from crashed spaceships, while working out whether craft used extraterrestrial technology to travel at such extreme speeds.