A number of ancient sites in Norfolk have been the target of nighthawking - illegal metal detecting on protected historical sites and farms - in recent weeks.

An area of land around Weeting Castle was targeted by seven men over three consecutive nights towards the end of January and beginning of this month – unfortunately no arrests were made.

An ancient site in Saham Toney has also been targeted.

Mark Harrison, national policing and crime adviser for Historic England, said illegal metal detecting is not a victimless crime.

'We may never see or fully understand the objects taken or damaged because they have been removed from their original sites with no care or record as to their history or context,' he said. 'The vast majority of detectorists comply with the law and have made a number of significant discoveries that have added to knowledge to our shared cultural heritage.'

However police have said the illegal activity is not on the rise but it is more prominent during this time of year.

PCSO Gavin Tampin, who is involved with Norfolk Constabulary's Operation Randall which was launched to help reduce rural-specific crimes, said: 'There is not a massive increase but it is the time of year - it is seasonal. A lot of the farms are now at that stage of being ploughed. When crops are grown up you cannot get out and metal detect.

'It has always been a background thing since it [metal detecting] became a popular hobby. There is always going to be lot of people out to flaunt the law.'

PCSO Tampin said the illegal metal detectors need to be caught by police committing the crime but advise people to not directly confront them.

Instead people should call 999 immediately and try to note down information including vehicle details, the action of the person, the equipment being used and what the person is wearing.

John Rigby, who is a member of the National Council for Metal Detecting, said: 'There is a code and a conduct with everything. It is about familiarising yourself them and the land.

'I think people who want to go out and do things like that bring the hobby into disrepute.'

Finding evidence of nighthawking

It is often found in the morning and in the form of holes dug in fields with no obvious explanation.

Other types of evidence that may be found are:

Footwear marks

Vehicle tyre marks

Discarded items

Call the police on 101 and notify them of the incident and tell them of the evidence left behind