CROP circle researcher and writer Lucy Pringle believes she has discovered what could be causing some of the annual phenomena that dot the Wiltshire landscape.

Scientific experiments that she has been involved in, she said, have shown a noticeable change in protein levels in crops affected and also discovered the presence of higher than usual electro magnetic fields.

Tests on humans who have been inside crop circles show changes in their hormone levels and brain activity, she said.

Mrs Pringle, whose home is in Petersfield, Hampshire said, however, that she has no evidence of what is causing the protein changes or the variation of electro magnetic fields.

She explains her new findings in a book simply called Crop Circles and published as one of the Pitkin guide book series, £3.50.

Mrs Pringle, a founder member of the Centre for Crop Circle Studies, has been looking into the cause of the phenomenon for many years.

She said: "I have been interested in them for years and years. I have always been interested in the unexplained since I was a child and so I fell quite naturally into the crop circle scenario."

In recent years, said the writer, she has been working with scientists carrying out tests on the effects of electro magnetic fields on living systems.

She said: "I think that crop circles are a by-product of electro magnetic forces when they hit."

But Mrs Pringle said what remains a mystery is where those forces emanate from and whether they are natural possibly emissions from the ionosphere she believes.

She has appeared on many radio and TV programmes on crop circles including Libby Purves' Mid-Week on Radio 4. She has lectured extensively in the UK and overseas and is a practising dowser.

Mrs Pringle will be at the National Trust shop in Avebury on Sunday May 2 to sign copies of her book.