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
Kilsby Tunnel presence of large amounts of quicksand; trial borings into the hill had not revealed any quicksand in the vicinity, but Stephenson had already made efforts to avoid any such an encounter being made. However, similar problems had previously been encountered during the construction of the nearby Blisworth tunnel on the Grand Union Canal only a few decades earlier. The problems that were posed by the quicksand, which was eventually revealed to be quite prevalent at tunnel level, were so severe that some considerations were allegedly made towards the abandonment of the shaft and restarting work afresh elsewhere; the resulting stress