ANGRY farmers say proposed restrictions on ploughing around an ancient monument could threaten their businesses.

Consultants are putting together a conservation study for the future management of Thornborough Henges, near Bedale.

One of the proposals is to restrict the depth of ploughing in an eight-square-mile zone around the henges.

It will include the villages of Nosterfield and Thornborough, extending to the outskirts of Well, Kirklington, Howgrave and West Tanfield.

The study, by Atkins Heritage, was commissioned by English Heritage and the Thornborough Henges consultation group.

A public meeting was held on Wednesday for local people to hear more details about the study.

Project manager Andrew Croft said the aim of the study, which is expected to be completed by March next year, will be to assist decisions on planning applications, archaeological research and landscape management.

He said when the study is complete it, "would have no formal status".

Farmers at the meeting challenged the size of the area chosen for the study and said restrictions on depth of ploughing could affect production of potatoes and sugar beet.

Potato farmer David Robinson, of Howgrave Hall, said: "If a restriction on the plough of 8in is agreed, then I am out of business.

"We operate a substantial potato-production business and I am seriously concerned."

Farmer and landowner Christopher Bourne-Arton said: "The outcome could affect all types of landowners, be it a house, a garden, a paddock or a business."

The area designated for the study includes Nosterfield Quarry, owned by Tarmac, which has a planning application currently in progress for further sand and gravel extraction at Ladybridge.

The Thornborough site is said to contain the greatest concentration of late Neolithic and early Bronze Age henges - or circular monuments - in the country.

It is thought they may have been the most important sacred site in Britain 5,000 years ago.

Mike Sanders, from the Friends of Thornborough, said: "We would expect that the plan, when it is completed by the consultants, would include recommendations to compensate farmers for accepting a management plan that curtails their free use of their own land.