Archaeologists are to team up with police in a bid to crack down on illegal metal detecting in Norfolk.

Norfolk has the highest number of recovered artefacts in the country declared treasure and a successful long-established working relationship with legitimate metal- detecting enthusiasts.

There were 109 cases of items found in Norfolk being declared treasure in 2008-09. Recent finds include a hoard of 24 Henry III short-cross pennies in Breckland, and an early Saxon gold spangle from south Norfolk.

But illegal metal detecting, known as "night-hawking", is a big problem and Norfolk Archaeology Unit (NAU) is to prepare a briefing note for

police safer neighbourhood teams outlining some of the worst affected areas.

Former Roman sites, such as Caistor St Edmund, are believed to be a particular target for night-hawkers, as well as the area around Snettisham in west Norfolk.

But night-hawking is a county-wide problem and has raised fears among archaeologists and legitimate metal- detecting groups that valuable artefacts are being lost - or sold online for profit.

Dr Andrew Rogerson, senior landscape archaeologist at NAU, said Norfolk was the county with the best set-up for legitimate metal detecting, which was why night-hawking needed to be tackled.

"Norfolk has a national reputation as a place to come and filch and steal archaeological material," said Dr Rogerson.

"It's a huge problem and it's enormously widespread.

"We have started liaising with police and one of the things we have done is produce a map for them of the most obviously plundered sites.

"The only way of solving it is to have really proactive farmers and gamekeepers," he added. "By definition we don't know what they find, but we can assume that they find the same range of material as legitimate people and then they will flog it on the internet."

Kevin Elfleet, from the King's Lynn Metal Detecting Club, welcomed the initiative.

"It is a problem," said Mr Elfleet. "A lot of them are from other counties. Some of them have threatened farmers and their families and people feel intimidated by them. It's a fairly organised thing."

A Norfolk Police spokesman said the briefing document was still in a draft stage, but the force was happy to co-operate on the crackdown.

"We are working with Dr Rogerson and we are supportive of his efforts," he said.