The first national survey - carried out by the Government's own countryside advisers - reveals that 87 per cent of the country's 70,000 miles of drystone walls are deteriorating or derelict.
Only 4 per cent are in excellent condition, and only a further 9 per cent can be described as "sound".
More than 2,500 miles of wall have disappeared altogether over the past 10 years, and the survey, by the Countryside Commission, shows that another 12,000 miles are now mere "remnants", little more than lines of stones on the ground. Some 8,500 miles are totally derelict, and more than 40,000 miles are deteriorating or in the early stages of dereliction.
David Gear, the commission official in charge of the survey, which examined the walls in detail all over the country, said he had been shocked by the results.
"Walls that look sound from the air, or show up as lines on the large- scale Ordnance Survey maps, in fact turned out to be in very, very poor shape," Mr Gear said. "These could be lost very quickly, unless something is done now to address the problem."
Many of the walls are now no longer needed for agriculture. Many were built in response to the Enclosure Acts, which laid down that they should be used to demarcate land, and others have fallen into disuse as field sizes have grown.
They are extremely expensive to repair: it costs pounds 20-pounds 30 to repair every yard of the thousands of miles of walls. But the Government is failing to protect the walls and is reducing incentives for farmers to look after them.
The new Environmental Protection Act, passed this summer, contains special provisions for safeguarding hedges, but ministers refused to give the same protection to the walls, despite the pleas of the Countryside Commission.
Earlier this year the Ministry of Agriculture reduced the level of grants paid to farmers to maintain them, and there is evidence that repair work slowed down dramatically as a result. Next April the ministry plans to abolish the main source of the grants - the Farm and Conservation Grants Scheme - altogether.
"Walls are appreciated by everyone - ramblers, photographers, artists and writers - but farmers need financial incentive to preserve them," said Mr Gear. "Putting new resources into wall restoration now, while the problem is still manageable, would help to protect these cherished livestock features for many years to come." The National Farmers' Union is dismayed by the impending abolition of the grants and has been lobbying for the retention of the scheme at the political party conferences this autumn.
Grants will continue to be given in limited Environmentally Sensitive Areas, but the Countryside Commission and the National Farmers' Union believe that a national scheme is essential. The commission is proposing that a new scheme should be set up when the old grants disappear, and is in negotiatoin with ministers to press for it.