Left: the 12 chambers were found in the stone abutment to the left of this image.

Visitors to Clifton Suspension Bridge can see images of chambers sealed since 1840.

A series of huge vaulted chambers has been discovered within the structure of Bristol's magnificent Clifton Suspension Bridge.

Maintenance work undertaken last summer revealed a possibility of the existence of a shaft running through the stone abutment on the Somerset side of the Avon Gorge.

Abseiling specialists went down to investigate and discovered a tunnel leading to 12 huge chambers 11 metres high and 15 metres long, linked by narrow shafts and tunnels.

"They are two thirds of the height of the nave of Bristol Cathedral, almost three double-deckers," explained Mike Rowland, manager of the Visitor Centre.

"Engineers were doing some paving works and they discovered there was a hole down there. They were the first people in there since 1840, so when the last work man died, the knowledge of it went with him."

The famous bridge was completed by Isambard Kingdom Brunel in 1840 and although the original plans are held by Bristol University none show the design of the abutment.

"It was always assumed that it was solid," said John Mitchell, Bridge Master.

"The theory was reinforced by a borehole investigation in 1969 which, by chance happened to go through a solid part of the structure."

Although it is believed the chambers were incorporated to save on building materials, safety has never been compromised and engineers have declared the bridge structurally sound.

Nothing was found in the chambers except for a number of stalactites, which have grown up to four metres in length.

Unfortunately there is no public access to the shafts; however, an exhibition of photographs and drawings of the amazing discovery is on display at the Visitor Centre.