By Sarah Mukherjee
Environment correspondent, BBC News
John Browning's land has been targeted by looters
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.
On a crisp, clear February afternoon, Suffolk farmer John Browning is walking his fields.
It does not take him long to find what he is looking for. A hole, crudely dug by treasure hunters out to loot the site of its Roman and Saxon antiquities.
John's farm lies in a nexus of ancient pottery kilns, Roman roads and villas, and Saxon settlements. He spends a good deal of his time trying to see off those who come to steal.
"It doesn't make for a quiet life", he says.
"We have now caught 50 people. In the early days, everyone was prosecuted. Now those not 'known to the police' are let off with a caution.
"The penalties, if anything, are diminishing, from a low base.
"If a man - or woman - were caught with a pickaxe handle trying to break off a stone from St Paul's Cathedral, I expect the penalties would be severe. But people are regularly destroying our heritage and get a fine less than a parking ticket."
It is in part to highlight the plight of John, and the hundreds of other landowners who are trying to protect these precious sites, that English Heritage is publishing a survey of the best and worst sites for illegal metal detecting - or "nighthawking".
It wants to make the public aware that - while for the vast majority this is a gentle pursuit, involving fresh air and maybe finding the odd coin or buckle from times past - for a minority it is an organised and sometimes violent crime.
It is also urging the Crown Prosecution Service and magistrates to take it more seriously.
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.
"We want people to see the magnitude of what's going on", says Greg Luton from English Heritage, who has joined John on his walk.
"Once these things are removed, their provenance disappears and that makes the object almost valueless from a cultural point of view.
"This is a finite resource - once it's gone, it's gone."
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.
"The ones that do give permission realise that it can be valuable," says Bob White, an enthusiast in Lewes, East Sussex.
Bob White is happy to co-operate with landowners
"We keep an eye on their land - telling them, for example, if an animal is lame or a fence is down".
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.
"Fresh air, the outdoors, perhaps discovering something new - you can't beat it. But don't think you are ever going to make your fortune with a metal detector."