Here is the story as it was sold. On the afternoon of Sunday 7 May 1989, a naval vessel off the Cape picks up a fast object on radar. It crosses into South African airspace at nearly six thousand knots. Two Mirage F1 fighters scramble from Air Force Base Valhalla. The lead pilot gets a visual, then fires an experimental laser cannon, code-named something like Thor, and the object wobbles, loses height and ploughs into the Kalahari near the Botswana border. The crater is a hundred and fifty metres wide. In it is a silver disc, and out of the disc come two small figures in grey suits. A recovery team seals the area, radiation is measured, and in June the two occupants are quietly flown to Wright-Patterson Air Force Base in Ohio.

It is a superb story. It has everything. It also has no witnesses at all.

The whole thing arrived in Britain in 1989 as a sheaf of documents, stamped top secret, in the hands of a young South African who introduced himself to the Yorkshire-based group Quest International as an air force intelligence officer. Tony Dodd and Graham Birdsall of Quest were shown credentials, transcripts, even tape recordings of a senior officer dressing him down. They ran with it. Within months the Kalahari crash was on conference stages and in magazines across Europe, and it has never quite left them.

The unpicking took less time than the spreading. Cynthia Hind, the Zimbabwean investigator who a few years later would interview the Ariel School children, wrote a piece bluntly titled Anatomy of a Hoax. The documents were in English rather than Afrikaans and were riddled with schoolboy errors. They used Greenwich time, mixed metric and imperial units, misspelt Kalahari, and put the alert on a Sunday afternoon at a training base with no interceptor role. The naval vessel named in them was not a frigate but a fleet tanker. A Mirage cannot keep pace with an object doing six thousand knots for long enough to see it, let alone shoot it. The forged seals, on close inspection, had been copied from a South African passport and a birth certificate.

The intelligence officer turned out to be twenty-four, not twenty-six, and not an officer of anything. He had founded a small UAP society, appeared on South African television to recruit members, and left a trail of unpaid hotel bills and a bounced cheque behind him. In Germany he told sympathetic researchers he had been sentenced to death by the military for leaking the file, and asked for money. Later, in a back room at a conference, he admitted to Dodd that he was an enthusiast who had made it up. He said he had wanted to see whether the UAP world would swallow it.

The South African Defence Force’s public relations officer, asked to comment, said he had nothing to add about the flying ducks that appeared in the press from time to time.

That should have been the end. But hoaxes have long half-lives. In 1996 an anonymous letter describing a second crash, this time in Lesotho, cross-referenced the Kalahari incident as established fact. It too fell apart under a week of phone calls. The Kalahari crash now lives on as a case study in how a story with no witnesses can outlast the man who invented it. The sand north of Vryburg has no crater in it, and never did.