A JELLYFISH-SHAPED crop circle has mysteriously appeared in a field near an ancient burial chamber.

The 600ft by 250ft pattern on farmland near Ashbury – just a few miles from the iconic Uffington White Horse chalk landmark – appeared at the weekend.

Experts are claiming it to be the first of its kind in the world and said that as well as looking like a jellyfish, it also replicates the Earth’s magnetic field.

The circle was found in a barley field at Wayland’s Smithy – a burial chamber close to the ancient Ridgeway trail – off the B4507 from Ashbury to Uffington.

Francine Blake, Wiltshire Crop Circle Study Group founder, said: “Although this isn’t the largest crop circle, it’s fantastic, because of its size and quality of design. It’s just amazing.

“Oxfordshire has had a lot of really good crop circles. The White Horse Hill and Rollright Stones are two hotspots. Those around the Ridgeway are really beautiful as well.

“We arrived on Sunday but believe it had been there four or five days and probably came when it was raining.

“It has a criss-cross style throughout and a very fine design.

“When we look at it, it’s got seven small circles, or moon shapes. It’s describing the magnetic field of earth.”

Various theories abound about how crop circles are formed, including by UFOs, unusual forms of lightning or by someone stamping the crops down.

Ms Blake, from Devizes, who founded the group in 1995, said: “We don’t know how crop circles appear.

“We know they come very quickly, because of the change in the crop plants.

“They are heated from the inside, caused by a hot blast of energy that hits a particular spot. The crop cells become swollen and are bent down and the design is formed.”

The group has about 6,000 crop circles on its database.

The biggest was discovered at Milk Hill in Devizes in 2001. It was made up of 407 circles.

Richard Henderson, spokes-man for the National Trust, which manages Wayland’s Smithy, said: “We have always taken the view that they are common to this area and are nearly always associated with ancient sites such as the White Horse, Wayland’s Smithy, Avebury and Stonehenge.

“Of course, all the sites have an air of mystery about them and this adds to the phenomenon.

“We should not forget that for the farmers, whose crops have been damaged, they are quite a nuisance.”