Illegal metal detectorists who fail to declare historic finds are being targeted in a new national campaign being led by Essex Police.

Operation Chronos will see officers team up with Historic England and others to encourage land owners to report the practice, known as nighthawking.

As well as committing trespass, nighthawkers can steal artefacts for both their historical and financial value and often damage farmland, disturb wildlife and destroy archaeological sites at the same time.

Because objects taken are stolen property nighthawkers are unlikely to report their finds, leading to valuable historic data being lost for good.

Counties such as Essex are particularly vulnerable to the crime due to the combination of rich heritage and large amounts of arable land in these areas.

Assistant Chief Constable Julia Wortley, Essex Police lead on territorial policing, said: “So-called nighthawkers might think they’re no different to people who go metal-detecting for a hobby, but their actions damage the countryside, threaten our heritage and lead to the loss of important and invaluable national artefacts simply to satisfy the greed of a small group of criminals.”

Pc Andy Long, wildlife, heritage and environmental crime officer at the force, added: “Most people who metal detect as a hobby abide to the law and codes of practice and have a love of the outdoors and history, respecting farmland and other surroundings.

“Nighthawkers seriously damage that good reputation.”

In a bid to tackle the issue landowners are being asked to take registration numbers of vehicles and descriptions of people involved.

They should also look for evidence of nighthawking, such as finding holes dug in fields with no obvious explanation, foot or tyre marks, and litter.

There have been few recorded incidents of nighthawking in Essex in recent years, which has partly prompted the launch of Operation Chronos today.

In late 2011 Essex Police made an appeal after a metal detecting event in Twinstead uncovered a large number of Victorian and Edwardian gold sovereigns, valued at £350 each.

Only two coins were handed in on the day, with a further 38 reported after an initial appeal, but officers had to track down others who were not as diligent including one person who was reported to have left with 70 of the sovereigns.

Any finds must be reported to the coroner’s office within 14 days.

There is a fine of up to £3,000 or three months imprisonment for failing to report treasure.