A study has concluded that many of the UK's historic sites are under threat from illegal metal detector users. History enthusiasts are frustrated that little is being done to prevent the damage.

One landowner tells of discovering a gang armed with bicycle chains and other weapons, as well as dozens of maps, highlighted with sites of historical interest.

Responsible metal detectorists, as they are called, are just as angry about what the criminal minority do in their names, saying that it makes it very difficult to establish relationships with landowners.

Bob, and his friend Cliff Smith, are members of a recognised national body with insurance and a strict code of conduct.

When they found a very significant Saxon site in the area recently, they got in touch with the authorities, helped with the dig and even camped out overnight to make sure that the nighthawkers did not loot the site.

But Cliff points out a flaw in the current system of cataloguing recent finds.

"Once a site is scheduled, it goes on the internet", he says.

"You might as well put the GPS co-ordinates on with a sign saying 'dig here'. The archaeologists rarely have the resources to properly dig a recently discovered site. When they run out of money the rest is effectively left to the looters."

But Bob says that despite these frustrations, going out detecting is one of the best things in the world.