Some of the oldest highways in Britain, built over 5,000 years ago to guide Bronze Age man across the treacherous wetlands of the Somerset Levels, have been completely destroyed by modern agriculture.
The scientists, who carried out the first systematic survey to assess the scale of the damage, described their findings as "quite shocking, but not unexpected."
They opened small trenches to check sites which, excavated over the last century, once held startlingly well preserved organic remains illuminating how prehistoric man lived, hunted and fished in a landscape more water than solid ground - making them some of the most important wetland sites in the world.
This time the scientists found that as the land has been drained, particularly with the use of more powerful pumps since the second world war, almost all the sites have been seriously damaged, and many destroyed. Two track ways, both scheduled ancient monuments, have disintegrated completely, leaving only smears of dust in the soil and the odd scrap of pottery and flint. Another two have probably been destroyed, since the scientists failed to locate them - even though they were in pasture land, generally regarded as far less damaging to archaeology than tillage.
They found the Iron Age lake village at Meare, an internationally famous site, so damaged "that the only remaining organic components were shrivelled and contorted wood fragments". Waterlogged peat is 90% water, and originally preserved the stakes, wicker frames and plank surfaces of a network of tracks across the bogs, and of fish traps and village sites. Many are now permanently above the water level, even in wet winters: as the soil dries out, the ancient wood simply disintegrates.
The only sites which remain in good condition are part of the Sweet Track, a main road built around 5,800 years ago, in a nature reserve where the original water level is maintained, and the Glastonbury Lake Village which is owned by a trust: the suggestion is that if both were on privately owned farmland they too might have been destroyed.
The survey was jointly carried out by English Heritage, the Environment Agency and Somerset County Council, and will be reported in detail in the November issue of British Archaeology. The scientists believe their bleak findings are probably also true of sites such as the Lincolnshire Fenland. The only hope lies in persuading farmers to join agricultural stewardship schemes, which compensate for a return to traditional low impact agricultural methods. Richard Brunning, of Somerset County Council, said bleakly: "At least we now know."