Gary Heseltine, a British Transport Police officer, has produced an annual report detailing UFO sightings by officers across the country since 2003.
His latest report, published on his PRUFOS (Police Reporting UFO Sightings ) database this week, highlights 50 new cases involving 106 officers - taking the total of individual sightings recorded to 310.
The 48-year-old said: "Police officers are trained to give dispassionate, detailed descriptions of things they see and are highly credible witnesses as a result."
Mr Heseltine said he set-up the database in the mid-Nineties after he found a UFO magazine full of highly credible accounts of sightings by military pilots backed up by radar evidence.
He said one of the most startling reports on it is that of PC Alan Godfrey, who spotted a diamond-shaped UFO levitating above a road in Todmorden, West Yorks, in 1980.
He tried to call for help on his police radio but it had stopped working. He then tried to get out of his car but was blinded by a white light. Pc Godfrey's next conscious memory is being back in his car, further down the road, with the UFO having vanished.
Under hypnosis he claimed he was taken up into the spacecraft and examined by small creatures.
Since starting the database Mr Heseltine, a detective constable from Wakefield, West Yorkshire, who has two grown-up children, claims to have made two UFO sightings.
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