UP to 7,000 historic archaeological sites in the North-East and Yorkshire could be at risk as a result of present-day farming, English Heritage has warned.

The warning coincided with the launch of its campaign aimed at protecting valuable heritage.

Ripping Up History is intended to look at ways in which the past can be protected.

English Heritage said that since 1945 some of the country's oldest visible monuments have been destroyed or seriously damaged as a result of ploughing using increasingly powerful farm machinery.

Roman towns and villas, Anglo-Saxon cemetries and precious objects such as goblets are all at risk.

Although legislation protects these monuments from most threats, in many cases it permits them to be ploughed, even though ploughing can damage fragile and irreplaceable archaeological remains.

Farmer Ian Grice has applied for a Department of Environment, Food and Rural Affairs Countryside Stewardship scheme to help protect the remains of the medieval village of Hanging Grimston which is beneath a field on his Mount Pleasant farm at Kirby Underdale, near York.

He said: "I am as concerned about looking after this valuable historical site as anybody, but farmers need more help as we have to make a living off our land."

A spokesman for the National Farmers Union in the North-East called on the Government to work with councils and archaeologists to ensure farmers are told about the location and importance of remains.

The spokesman said: ''In the majority of cases, damage that has been caused to these sites has been the result of farmers not being informed about the sites rather than as a result of any malicious intent.''