More of Dorchester’s rich underground history has been discovered beneath one of the town’s most iconic buildings.

A below-ground passageway dating back to the 17th century was discovered beneath Shire Hall by builders currently renovating the historic building.

Flummoxed by what it could be, the expertise of town and district councillor David Taylor were called upon.

Cllr Taylor, who has spent years piecing together the vast network of tunnels, passageways and rooms which lie beneath the county town, said the discovery was “fascinating.”

He said: “The tunnel shows us five stages of history. There are the original chalk beds on which Roman buildings were built upon as well as some Portland Stone and some Medieval flint which dates back to the 13th century.

“There was also some blackened brick from the great fire of 1613 which Shire Hall would have been built on top of in the 1700s. It’s really interesting to find chalk and flint as that means you are on the original bedrock of Dorchester.”

The tunnel is one of around 20 so far uncovered by Cllr Taylor and his team of underground investigators.

Previous discoveries have included a passageway believed to be used by the renowned Judge Jeffreys, a Roman mosaic and the remains of an Elizabethan house.

He said: “After the great fire they built a complete tunnel system, so that if a fire ever happened again they could escape, and then on top of that they built Dorchester again.

“It’s just so interesting to see the deep, rich history of Dorchester which we are constantly uncovering. People just do not understand what they’re walking over as they walk down the high street.”

The passageway in question has been modified with new bricks which Cllr Taylor said would have been added when High West Street and East Street were dug up in the 1980s to lay the service foundations for new Poundbury.

Project director Anna Bright, of the Shire Hall Trust, said the construction team were shocked to discover the tunnel so late in the project as the multi-million pound renovation is set to open to the public next year.

She said: "We have had some people come in to check the tunnel and make sure it’s completely safe and we’ve had historians in to have a look around, but they weren’t sure what it was for, or what the point of it was, that’s when I thought of David."

Plans are now underway to install a trap door above the tunnel for visitors to take a peak at Dorchester's buried history.