A group of British UFO-watchers is celebrating 50 years of searching for spacecraft in the sky. What keeps them looking for extra-terrestrial life?

There are no windows in the functional-looking basement hall beneath a north London hotel. But everyone gathered here is gazing to the heavens.

Figuratively speaking, that is.

The annual conference of the British UFO Research Association (Bufora), is a gathering of enthusiasts for unexplained aerial phenomena that might, they speculate, be evidence of extra-terrestrial intelligence.

Dozens of them have travelled from around the UK to be here. They listen to guest speakers patiently and attentively. Many carefully take notes during lectures on such topics as "Ghost Rockets", "Political, Cultural and Social Influences of UFOs" and "Behind All The Anomalous Reports".

Ufology - as its followers like to term it - is a subculture with its own lexicography - greys, contactees, close encounters.

Image caption Bufora delegates browse UFO titles at a bookstall

The ufologists also have their own recurring motifs - abductions, government cover-ups - and a distinctive visual aesthetic which looks like a sort of blend of the retro-futurist and the New Age.

At a bookstall, delegates browse titles like The Real Men in Black by Nick Redfern, Reflections of a UFO Investigator by Kevin Randle and The Occult Significance of UFOs by Douglas Baker.

The predominant demographic is older men. But somewhere between a quarter and a third of Bufora attendees look under 30 and a similar proportion are female.

Bufora styles its approach as "scientifically factual", distancing itself from the more esoteric and mystical wings of the movement, such as the Raelians, who believe the Earth was created by an alien race called the Elohim, and followers of David Icke, who teaches that the human race was bred by reptilians from the constellation Draco.

Close Encounters of the Third Kind caused a membership surge Matt Lyons

Instead, Bufora devotes its efforts to fact-checking unexplained sightings. The group says that 95% of the 500-plus sightings reported to its National Investigations Committee each year can be explained rationally. And the rest - well, they aren't ruling anything out. Not aliens, anyway.

This logic, and indeed the very notion of an empirically rigorous UFO-spotter, is guaranteed to provoke snorts of derision from sceptics who regard ufology as a blend of pseudo-science, conspiracy theory and mystical hokum.

Certainly, speakers may stress the importance of maintaining an evidence-based approach and not letting one's beliefs colour judgements.

But the questions from the floor tend to concern whether they think a spacecraft landed at Rendlesham Forest in Suffolk in 1980 or if they believe the American government is covering something up at Area 51 in Nevada. No-one demurs when the TV presenter Lionel Fanthorpe tells the audience that the "major possibilities" for explaining strange things in the sky include parallel universes, extra-terrestrial life and "psychic phenomena".

But even opponents would have to concede that the ufological world view has seeped into the mainstream. A study for National Geographic magazine in June found that 36% of Americans said they believed in UFOs and one in 10 claimed they had spotted one. Almost 80% thought the government had concealed information on the subject from the public.

Nonetheless, the last decade has seen a succession of news reports foretelling a crisis in ufology.

Is it a bird, is it a plane? Numerous UFO sightings in the UK were published by the National Archives in 2012, but UFO-spotting is nothing new, with many cases being recorded in different countries: 1946 - Polish-born American George Adamski claimed to have seen a large cigar-shaped "mother ship"

claimed to have seen a large cigar-shaped "mother ship" 1947 - reports of an object crashing near Roswell, New Mexico was thought to be an extra-terrestrial spacecraft. The US army countered that debris recovered belonged to a weather balloon

was thought to be an extra-terrestrial spacecraft. The US army countered that debris recovered belonged to a weather balloon 1980 - The Rendlesham Forest incident, when lights and a craft were reportedly seen in the forest in Suffolk near RAF Woodbridge

The folding of the long-established UFO Magazine in 2004 and the Ministry of Defence's decision to close its UFO desk in 2009 led several mainstream commentators to conclude that the phenomenon was a distinctively 20th Century one, unique to an era of Cold War paranoia, space race-fuelled technological optimism and pop culture references to aliens and extra-terrestrials.

There was even speculation that the effect was partly down to 9/11. With a new and definitely real enemy to focus on, the uncommitted would be less drawn to ufology, the theory went.

But still the ufologists gather, longing to discover more about these strange sightings in the sky.

"[The movie] Close Encounters of the Third Kind caused a membership surge for us, as did ET and then the X Files," smiles Bufora chairman Matt Lyons, a cheerful 45-year-old music teacher from Kent.

While unexplained celestial happenings have been witnessed throughout history, UFO-spotting as a popular phenomenon took off after US airman Kenneth Arnold reported sighting nine disc-shaped objects while airborne in 1947. Five years later, George Adamski attracted huge publicity after claiming that he had met Nordic-looking aliens who warned him about the dangers of nuclear war.

Against this backdrop, Bufora was founded in September 1962 as an amalgamation of various regional groups.

Mainstream scientists were not yet embarrassed to be associated with UFOs, recalls retired civil servant and veteran UFO-watcher Lionel Beer. The Duke of Edinburgh was even claimed as a subscriber to Flying Saucer Review. At Bufora's inaugural meeting, in west London's Kensington Central Library, it was "standing room only", Beer wistfully remembers.

Arguably the high point of ufology's influence on British political life came when the House of Lords earnestly debated the subject in January 1979.

By this time, however, sky-watching had taken a darker turn. In the believer's worldview, aliens had been the wise, benevolent secular angels of Adamski's depiction.

But by the end of the 1970s belief was growing in a huge government cover-up at Roswell, Nevada - a plot that, coincidently, began to be speculated about soon after the Watergate scandal shattered public faith in politicians.

Indeed, it's possible to see postwar Western social history reflected through the prism of UFO belief - from early optimism about technological advance through Cold War fears of attacks from above, via 1960s counterculture and the later cynicism that would find its zenith with the X Files.

For this reason, even sceptics like Dr David Clarke of Sheffield Hallam University - who successfully campaigned for the MoD to release its UFO-related files - believe the phenomenon is nonetheless worth studying as a powerful example of 20th Century folklore and mythology.

"Of course, it's pseudo-science," he says. "But people have always looked in the sky and seen things that were odd or puzzling. Before aliens, it was angels, ghosts and spirits.

"What it tells us is that, as human beings, we need to find explanations and believe in something bigger than ourselves."

Not that all non-believers entirely reject life in the ufology world.

Writer and film-maker Mark Pilkington - whose book about the subculture, Mirage Men, forms the basis of a forthcoming documentary - has fond memories of his early days in the UFO community before he abandoned its core tenets.

"If you get into it and take it seriously, you have to learn about physics, chemistry, meteorology and so on," he says.

"It can give you a really good grounding in reality, ironically."

Even the sceptics, it seems, are staring at the stars.