Officers are on the muddy trail of rogue metal detectorists who struck at a scheduled Grade 1-listed Cotswold pilgrimage site that was famously mentioned in Chaucer's Canterbury Tales.

Hailes Abbey, near Winchcombe, was visited by 'nighthawkers' – detectorists who set out to steal ancient metal artefacts with no landowner approval and who sell their ill-gotten gains on to unscrupulous collectors through black-market connections, as well as Facebook Marketplace and Ebay.

Eight holes were found at the site, which is owned by the National Trust and managed by English Heritage, as tell-tale evidence of the thieves' calling card.

The illegal activity, which falls foul of the Criminal Damage Act 1971, the Ancient Monuments and Archaeological Areas Act 1979 and 1996's Treasure Act, happened on the night of Wednesday August 20 to Thursday August 21.

Metal detectorists in the UK are largely represented by the National Council for Metal Detecting (NCMD) which works to proactively reinforce good and legal practice for the hobby among its membership, which now boast nearly 40,000 detectorists.

In a recent interview, NCMD spokesperson Catherine Lange said: "We want it called what it is, which is theft." 

Any romanticism around the word 'nighthawking' could, she warned, lead to the crime not being taken seriously and undermine efforts by detectorists to ensure their hobby's reputation isn't tarnished.

A police spokesperson said: "The [Hailes Abbey] site is protected by law and therefore metal detecting of this nature, commonly known as nighthawking, is illegal. Investigating officers are asking anyone with information on those responsible to make contact."

The force is also hopeful that information will be passed on from the incident for progress in its current 'Operation Minster' which stems from a new Heritage Watch scheme launched by the county's force in 2023 after "lasting damage" was caused to the Grade-I listed Cheltenham Minster through vandalism.

In a media interview in May, Mark Harrison, Head of Heritage Crime at Historic England, said rogue detectorists were "stealing from all of us and damaging something which is often irreplaceable".

While he added that most metal detectorists adhere to the law and and codes of practice, a perceived trend in nighthawking now posed a serious threat to the country's heritage, though he acknowledged that "significant progress" has been made tackling heritage crime.

According to English Heritage, Hailes Abbey dates back to the 13th century as a place of prayer and pilgrimage: "It belonged to the Cistercian order, which favoured a simple and disciplined style of worship," the guardians said.

They added: "The church's east end was rebuilt early in its history to house a holy relic: the Holy Blood of Hailes. Given the power of such claims at the time, therelic brought fame to Hailes Abbey and Geoffrey Chaucer even referred to the monastery by name in The Canterbury Tales."

Aside from nighthawking's modern menace though, the site suffered a more lasting calamity exactly 400 years before the outbreak of WW2, after Henry VIII's infamous Suppression of the Monasteries.

In the Tudor king's attack on Hailes Abbey in 1539, the relic was destroyed and the building left in ruin in the ruins now seen today.

Official excavations were carried out by the Victorians and again in the last century, with the site now recognised for its surviving stonework and visitor museum as a significant monument to English monastic history.

In 2021, The Archaeology and Metal Detecting Magazine suggested nighthawking activity had reached "epidemic" levels in the UK.

In February this year, the Forest of Dean Buildings Preservation Trust alerted police to an incident in the churchyard of Lancaut Church, at Tidenham, after nighthawkers were found to have excavated a series of holes across the burial site. The masonry and grounds of the church are protected due to their archaeological value, which is of national importance.

● More information on the Force's Heritage Watch Scheme can be found here .