Blisworth Tunnel has no tow path inside, but is wide enough for two narrowboats to pass in opposite directions. Work began in 1793, but errors by contractor left a wiggle in the tunnel, and after three years work it collapsed due to quicksand, claiming the lives of 14 men. It was then decided to begin again with a new tunnel. By the time the rest of the Grand Junction Canal had opened between London and Braunston, Northamptonshire in 1800, apart from the crossing of the River Great Ouse, the section of canal from Blisworth to the lower end of Stoke Bruerne locks
Southampton Tunnel partial construction of the Salisbury and Southampton Canal tunnel, which the railway tunnel crosses at an acute angle and slightly higher. Because the canal tunnel was lined with clay "puddle" it collects water which ends up in the rail tunnel making the latter very wet. In the 1960s an access was cut into the canal tunnel in order to examine it, although this was later sealed behind a new segmental wall structure when, between 1983 and 1985, the tunnel underwent extensive engineering works and the line through it was worked as a single line for long periods while remedial work