A crop of circles

They appeared overnight in fields in southern England in the 1970s, and spread over the world — and over acres of summer newsprint.

Observers talked of balls of light and high-pitched noises over fields of wheat, and experts reached for their favourite "scientific" theories. One group favoured tornado-like vortices in the air, another suggested "directed plasma" while a third argued that ley lines focused a vital geomagnetic current through the earth.

Intelligent aliens were invoked, along with top-secret military experiments and gaseous toxins from below the soil. Some people claimed that the circles revealed mysterious scientific formulae or religious symbols, others that they had healing powers.

Then, in 1991, a pair of hoaxers confessed and showed the press exactly how they created their crop circles. Some buffs were not convinced, however, and still continue to invoke strange forces.