In the 1950s, George Adamski was one of the first to claim he’d been contacted by aliens. A handyman-cum-burger chef who lived near California’s Mount Palomar observatory, he produced a series of UFO photographs and wrote two best-selling books - Flying Saucers Have Landed and Inside the Spaceships.

Sexy blonde female Venusians took him on a trip to the moon, and a "master" explained that the aliens were here to save the solar system from nuclear radiation.

By the mid-50s, Adamski was expounding to a devoted audience the "cosmic philosophy" he had learned.

Adamski was eventually discredited. His tales had originally been written as fiction and rejected by publishers; repackaged as fact, they sold by the bushel. Adamski once remarked: "If it hadn’t been for Roosevelt, I’d never have had to get into flying saucers". He blamed President Roosevelt’s 1930s economic policies for ruining his literary career.

In the 1940s, Raymond Palmer was editor of Amazing Stories, the world’s oldest - and, at the time, worst - sci-fi magazine. It was on its last legs when Palmer began running wild tales of beings who lived underground and controlled surface mortals by means of strange "rays". He presented these not as fiction by as fact, and tapped into a rich vein of paranoia. By 1945, Amazing’s circulation had shot up to 250,000.

It was only a small step from underground aliens to space aliens, and by 1947 he had sold three key ideas to his readers: aliens who kidnapped humans, strange memory losses, and mysterious men from the government who were alien agents. The magazine was backed by "readers’ letters", mostly written by Palmer. By the time of Kenneth Arnold’s saucer sighting that June, Amazing had created a fertile soil for UFO-mania.

Dr J Allen Hynek, then a university astronomer, was hired by the US government in 1948 as a UFO consultant on Project Blue Book and Project Sign. Over the years he became concerned that the USAF didn’t want to explain things, just to explain them away. He felt the projects were under-resourced and under-ranked, never being run by senior enough officers. He did not suspect a government cover-up; as he put it, "they just didn’t care".

When Dr Edward Condon produced the 1,465-page negative report that closed down Blue Book in 1969, Hynek remained convinced that there had been no serious attempt to answer key questions.

In 1973 he founded the Center for UFO Studies, who International UFO Reporter, and Journal of UFO Studies are among the most respected publications in the field.