The strongest evidence so far that some crop circles are not man made was presented to a choice gathering at the Coronation Hall in Alton Barnes yesterday.

Norwegian film maker Terje Toftenes presented the DVD he has made of the extraordinary circumstances surrounding the creation of a massive crop formation in East Field, Alton Barnes, on July 7.

Most formations are discovered the morning after and some have even been created in fields with observers sitting on overlooking hills.

But on the morning in question, dedicated UFO hunter Winston Keech had a battery of cameras, from CCTV to state-of-the-art digicams, trained on the field on the off chance that something might happen.

He was joined by Gary King and his partner Paul Presdee-Jones, who had also decided to climb to the top of Knap Hill, near Alton Barnes, on a spur-of-the-moment whim.

They had already met the previous evening at the "croppies" cafe at Cherhill, near Calne, when Mr Keech had become rather excited about a DVD that was being shown about lights that sometimes accompany the appearance of crop circles.

He had explained that something similar had happened to him in 1990 when he all but witnessed the creation of a simple circle in crops in East Field.

Little did he know he would witness the creation of something a lot more complex.

At around 1.35am on July 7 Mr Keech, helped by Mr King, completed the last sweep of the area using a camera equipped with night vision. No formation was visible in the field.

Then it became intensely dark and nothing was seen. But at 3.13am there was a flash of what Mr Keech described as sheet lightning.

It appeared on the video footage and lasted four microseconds. Twenty minutes later, at 3.20am, there was enough light to make out the formation in the field below.

It was one of the largest ever seen. It measured 1,033 feet long and consisted of 150 circles, the largest of which was 164ft across.

Ms Presdee-Jones said: "We all went mad. Gary was dancing a jig."

Mr King told the gathering: "I had to be the first one in the circle. As soon as it was light enough to see where we were going, we went down.

"The corn had a glass-like quality to it and it snapped like glass when we stepped on it. My dog, Blue, went berserk.

"He is a dedicated meat eater, but he started eating the crop as though he was ravenous. Then he was violently sick."

Veteran crop circle investigator Lucy Pringle said the circumstances surrounding the formation made it very dramatic.

She said: "Because of the undulations in the field, it is impossible for someone standing at one side of the formation to see anyone standing at the other end.

"When I was standing in the centre of the formation, I couldn't see people in the lower part of formation."

Mr Toftenes pointed out another extraordinary element in the situation. He said: "Although from the air the circles look perfectly round, they are, in fact, ovals.

"Allowance has been made for the undulations in the ground and the only place you can see that the circles are perfect is from the air."

Mr King said: "The floodgates need to open now and allow all the research carried out by some very clever people to be made public.

"It is time to listen to all the people who have been looking at this phenomenon for so many years."

Ms Pringle said that samples of the crop have been sent for analysis to laboratories in Yorkshire.