English Heritage's annual audit of the historic environment, published this week, reveals that private farmland is facing vast repair bills and declining financial support from public sources.
The report states that 2,420 listed farms are in a severe state of disrepair.
English Heritage chief executive Simon Thurley, said: "It would take at least £30 million to restore the buildings that are at risk."
The study notes that planning applications have been submitted for 50 per cent of listed farms since 1980. Eight out of ten of these have been approved, with a third being converted to non-agricultural uses and the majority into residential buildings.
According to English Heritage, such developments detract from countryside character. It plans to publish guidelines next year on how to achieve "intelligent" farm building conversions. "We want recognition that repair of traditional farm buildings not only contributes to countryside character but creates jobs and supports skills," said Thurley.
He praised DEFRA's environmental stewardship scheme, launched this year, in which farmers are rewarded for good heritage and asset management.
But Thurley insisted that more must be done. "We want recognition of the vital roles private owners play in rural heritage and we need to find more ways to support them," he said. "We will continue to lobby for a flat rate of VAT on repairs and alterations and lobby for further grant schemes."
Heritage Counts 2005 is available from English Heritage Customer Services (tel) 0870 333 1181.