[1] It is named after Thomas Brudenell-Bruce, 1st Earl of Ailesbury (1729–1814), the local landowner, who, when the canal was being built, would not allow a deep cutting through his land, and insisted on a tunnel instead.

Located on the canal summit level, the tunnel was built to avoid the need for several locks that would have been required for a longer alternative route and while it was expensive to build the Earl insisted upon it instead of an unsightly but cheaper cutting.

It is driven through Upper Greensand Sandstone, brick-lined throughout and the portals – also in brick - are Grade II listed.

It is a large, two-way working tunnel 458m in length, 5.13m wide at water level and with a headroom of approximately 4.0m.

Both stations and the M&SWJR are long gone but the Network Rail main line from London to Penzance remains.