These caused roof falls and narrowing of the channel which continued after the tunnel opened in 1789 and required frequent maintenance.

The Thames and Severn Canal was authorised by an Act of Parliament on 17 April 1783 but details of the tunnel had not been worked out, and arguments about its size continued for two to three months.

[7] The use of explosives to expand the headings to the full size of the tunnel meant that acrid smoke and foul air built up.

[8] The construction contract was awarded to Charles Jones, who managed to build about one third of it, but then had financial difficulties, and so other contractors were engaged to work on smaller sections.

When the Fuller's Earth expanded this could lead to roof falls and pushed up the base of the tunnel reducing the depth of water for the boats passing through it.

[12] Further attempts to repair and stabilise the walls included the insertion of oak beams at the base to stop the sides of the tunnel moving inwards as the clay expanded and, in 1904, a concrete lining to some sections.

Strood Tunnel on the Thames and Medway Canal was 3,946 yards (3,608 m) when it opened in 1824, but was interrupted six years later by a short section to create a passing basin.

[1] The tunnel was passable until at least 1966, but is now blocked by roof collapses over several hundred yards, mainly in sections where the ground is fuller's earth.

[15] Restoration is proposed by the Cotswold Canals Trust as part of their project to re-open a direct route between Thames and Severn.

There have been proposals to pump water from the River Severn toward the periodically water-stressed Thames Basin; if so the tunnel and canal eastward could be used for this.