The Grand Union Canal opened in 1793. It ran from the River Thames at Brentford to a junction with the Oxford Canal at Braunston. The project also included Blisworth Tunnel, an aqueduct over the River Nene at Cosgrove and a long deep cutting at Tring.

The tunnel at Braunston is 1.87 kilometres long and lined in brick. It has no tow path and measures only 4.8m wide and 3.76m high. Before canal boats had engines, they were horse-drawn and so needed a tow path. To move along a tunnel without one, the crew would lie on their backs and propel the boat along using their legs against tunnel ceiling.

Errors were made in setting out the line of the tunnel at the bottom of one or two of the working shafts. Consequently, it has a slight S-bend in the middle. The contractors also discovered an area of quicksand some 300m long and had to sink additional shafts.

In 1870 a trial was conducted using an endless wire rope driven by steam engine to haul boats through the tunnel. The trial didn't work out and in 1871 a steam tug was brought in. The charge for towing boats through varied from 1s 6d for heavily loaded boats and a shilling for empty craft.

Contractors: Charles Jones, John Biggs