Rogue metal detectorists have been targeting Lydford Castle.

The damage to the site was reported to the police, site owner English Heritage and the Dartmoor National Park Authority by local archaeologist Dr Chris Smart.

Chris, who lives in Bere Alston, discovered the holes on a visit with his son Sampson and two friends two weeks ago when they were touring local castles.

He knew from his professional experience that the holes, which had been filled in again, were the work of ‘nighthawkers’ – illegal detectorists who operate at night.

Sampson’s friend Arnie Malone spotted the first hole and they went onto discover ten more on the site.

Chris said: “One of the kids asked me ‘what is that lump?’ I work with detectorists a lot in archaeology and I instantly knew someone with a detector had dug and backfilled the holes in front of the castle keep.

“Obviously, knowing the castle is a Scheduled Monument, it goes without staying that this is completely illegal and it was probably done by what are colloquially known as nighthawks, people who go in the dead of night when no one is around and dig. It does say on the castle sign in front of the castle that metal detecting is illegal.

He added: “I guess it was done in the week before we visited but we don’t know that has been taken, that is the problem. They could have had 11 signals that were rubbish bits of metal or ring pulls. We just don’t know.”

He said the three boys, who go to St Andrew’s Primary School in Buckland Monachorum, were angry at the discovery.

“They were quite angry that the someone was stealing bits of history. I was proud of them.”

English Heritage owns the historic site which has Saxon origins and is protected in law as a Scheduled Monument.

The site includes Norman earthworks and earlier town fortification dating from Saxon times. Lydford was one of just four sites in Devon which had a Saxon mint.

This produced silver coins, most of which ended up in Scandinavia to pay off the marauding Vikings, but a few of which can be seen in the Museum of Dartmoor Life in Okehampton.

A Devon and Cornwall Police spokesperson said: “We were notified following a report of a number of holes recently being dug at the English Heritage site Lydford Castle and Saxon Town without permission. At this time, there are no viable lines of enquiry however if further evidence comes to light the incident can be revisited.”

Michael Fife Cook, Reform UK county councillor for Yelverton Rural, said he “looked forward to the police apprehending these criminals”.

Cllr Fife Cook said: “I will continue to keep a keen interest in this crime as Lydford Castle is within in my constituency of Yelverton Rural. I look forward to the police apprehending these criminals. For these people to just come along and think that they can Illegally take away all that potential history beggars belief.”

The crime reference number is 50250125560. Anyone with information is urged to contact Devon and Cornwall Police.