The Ilkley Moor Alien Photograph (Philip Spencer)

Ilkley Moor is part of Rombalds Moor, the high ground between Ilkley and Keighley in West Yorkshire. Around the Twelve Apostles stone circle, multiple UFO sightings have been reported.

The witness asked to be called Philip Spencer. He was a former London Metropolitan policeman who had retired to West Yorkshire with his wife and child, to be near her family. On Tuesday 1 December 1987 he set out on foot across the moor to his father-in-law's home in East Morton. He carried a compass in case of fog. He also carried a camera.

Spencer said goodbye to his wife at about a quarter past seven in the dark, overcast morning. On the moor he heard a humming sound. Then something moving caught his eye. He turned and saw "a small green creature, no more than four feet tall, at a distance of about 30 feet or more." It had an oversized head and long, thin arms, and it shambled rather than walked yet moved much faster than a human.

The being turned and waved an arm dismissively at him. Spencer remembered the camera. He took one shot. The figure ran out of sight behind an outcropping. He jumped down the embankment in pursuit, into the fog.

What he saw next went unphotographed. "A large object like two silver saucers stuck edge to edge with a domed top" rose up from the moor and disappeared into a cloud. The hum was loud now. Later, he glanced up at the church clock, which read 10:00. By his reckoning it should have been around 08:15, and his compass now pointed south instead of north.

Jenny Randles heard from Spencer within days and put him in touch with investigator Peter Hough. On 16 March 1988 hypnotherapist Jim Singleton hypnotised him to explore the missing time, with Hough present. Spencer described paralysis, then being "lifted up a few feet and pulled into the craft." Green beings with "big pointed ears…big eyes" and hands of "three big fingers" examined him.

He was shown two films. The first showed "nuclear explosions, famines, and floods." The second, he said, the beings had forbidden him to describe. Singleton's view was that "Spencer was telling the truth as he knew it."

At Kodak in Hemel Hempstead, Peter Sutherst reported that the negative "had not been interfered with in any way." A wildlife expert called the figure "not an animal of any known kind." Optical physicist Bruce Maccabee found the film "too grainy for proper testing." About six weeks into the investigation, two men calling themselves RAF Intelligence officers, "Jefferson" and "Davis," came asking for the photograph, although RAF Intelligence said no such men existed. Author Nick Redfern later claimed the Ministry of Defence had sent them.

On 2 July 1989 the Daily Star claimed the "alien" was an insurance broker cutting through the hills. A similar newspaper story, of an insurance salesman on a bicycle, was later traced to a joke among staff. Sceptics answer that the image is too blurred to prove anything and could show a man or a cardboard cut-out. The craft was never photographed. A compass needle can be reversed artificially, and hypnosis changed the story substantially.

Nick Pope later listed the case among the top UFO incidents in the UK. It has been called one of the strongest pieces of evidence that extraterrestrials have visited Earth. It has also been called incredibly blurry.