A team of workmen removing a wooden pole to lay cabling have discovered a mystery tunnel in Tintern, Monmouthshire, which may date back to the 12th century.

The secret tunnel was uncovered in the historic village while technicians were moving overhead power lines to a different part of a customer’s property.

During this process, they had to dig a footpath along a fast-flowing stream, when they suddenly found a four-foot-high passageway underground.

The secret tunnel is thought to date as far back as the 12th century, but has not been marked on any maps since at least the 1700s.

Western Power Technician Allyn Gore said: “Before work began, we’d done all the usual checks and nothing had shown up on any of our drawings or records to indicate there was anything unusual about the site.”

However, once excavation began the team quickly made the discovery, which they initially thought may be a cave.

“Work stopped immediately and we were called in to decide what course of action we should take next” said Allyn in an interview with the Metro.

“I have previously been involved in other excavations where we’ve discovered old wells and cellars not shown on any plans, but nothing as exciting and impressive as this.”

The Welsh Government’s historic and cultural heritage service, Cadw, has since sent out a team to check out the unique discovery to assess it’s historic importance.

The tunnel has now been resealed to prevent the risk of damaging it before any in-depth archaeological examination can take place.

Situated in the heart of the Wye Valley Area of Outstanding Natural Beauty, Tintern is home to the remains of an abbey dating back to the early 12th century.

There are also a number of ruins from old furnaces, iron works and forges nearby, which could be connected to the tunnel.