But it was as an antiquarian that he made his most lasting impression - and his biggest mistake. It happened on a June day in 1921 when Watkins was visiting a friend near Leominster. Surveying the Herefordshire countryside, he was struck by the number of historic features - churches, burial mounds, ruined castles - that seemed to line up across the landscape.

Coincidence? Watkins thought not. To his mind, these alignments were evidence of an ancient civilisation - the visible remains of a system of dead-straight prehistoric trading routes. By the following year, he had so developed this theory that he would promulgate it through magic lantern shows.

Then, in 1925, he published The Old Straight Track, a book which was instantly popular and remains so to this day. Why has it survived? Because in the 1960s, the lines that Watkins thought he saw on that June day - “ley lines”, he called them - took on a new life.

It started when someone who knew nothing of Watkins began plotting French UFO sightings and decided that these occurred in straight lines.

In 1961, a retired pilot combined this observation with Watkins’s theories and put two and two together. If UFOs flew along ley lines, he argued, then these were not ancient trackways but lines of energy - a theory which so appealed to the modern mindset that it is now accepted as fact by a large section of the populace.

Of course the whole edifice of ley line theory would collapse if it could be shown that Watkins had blundered. As indeed he had.

In the 1970s, archaeologists at Cambridge University demonstrated that the supposed alignment of historic sites was nothing more than an illusion brought about by a profound ignorance of the laws of probability.

Inadvertently, though, they also demonstrated another truth: that people believe what they want to believe. For while science has exposed the error of Watkins’s ways, belief in the existence of ley lines is stronger than ever.

David Newnham