A West crop circle expert has lifted the lid on a previously long-forgotten chapter in the bizarre history of the West's 1990 crop circle mystery. Colin Andrews revealed to a coast-to-coast audience in America the goings-on under the cover of a summer night 15 years ago.

Mr Andrews, who left his West home for the US a decade ago, said that, far from being an embarrassing flop, the three-week vigil on the hilltops of Wiltshire was an astounding and secret success.

Listeners on US radio heard claims yesterday that the British Army watched and filmed a UFO making a ground-breaking crop circle near Silbury Hill while the world's media were camped 20 miles away.

Back in 1990, it was the high point of the crop circle hysteria gripping the world.

Dozens of volunteers, a host of foreign TV cameras, the world's foremost crop circle experts and the British Army launched a round-the-clock vigil from the famous white horse above Bratton, near Westbury, in a bid to spot a crop circle being made.

And within days it appeared Operation Blackbird had been successful - night vision cameras spotted something in a field below, and, sure enough, a new crop circle could be seen as dawn broke. For a few hours, the world reported the crop circle mystery as solved - but operation leader Colin Andrews soon realised he had been hoaxed and the figures on night-vision cameras were not aliens but local mischief-makers.

According to Mr Andrews, however, across Wiltshire a more mysterious and sinister event was happening, which has remained top secret ever since.

He said: "The public knew but half of what was going on at the time. While the media present at Operation Blackbird were looking at the right hand, they did not see what happened with the left.

"The British Army were looking at a secret site and a very important place nearby."

Strange things did happen at the Operation Blackbird HQ in Bratton - a strange hum, odd bass noises in the dead of night, and people seeing flashes of energy in the night sky.

"While, above Bratton, there was a formation appearing in front of the cameras which was supposed to convince the world of a hoax, the Army filmed a UFO at the secret site, and crop circles appeared next to the hill.

"The crop circle story will not be complete until Operation Blackbird is fully understood and why, and who, is behind the larger plan" added Mr Andrews.

Why he has chosen now to reveal more information now might have something to do with him winding down his research into the crop circle phenomenon. He recently put his entire collection of photos, videos, books, sketches and reports up for sale on eBay.