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The Grand Union Canal was formed from an amalgamation of several formerly separate canals. Until the 1920s these had been independently owned and operated. The original part of the system was the Grand Junction Canal between Braunston and Brentford, constructed to reduce the route from the Midlands to London by sixty miles. This had locks fourteen feet wide, many branches to major towns and broad beam boats carrying up to seventy tons. Earlier linking canals were built with seven foot wide locks.

The Regent's Canal acquired the Grand Junction and other canals in 1929 and created the new Grand Union Canal Carrying Company (GUCCC). In 1932, with government aid, extensive modernisation was carried out, including the widening of 52 locks between Braunston and Birmingham (Camp Hill), and the demolition and replacement of many 18th and early 19th century bridges; then the money ran out - and the World War II started, so the task was never completed.

Waterways absorbed into the Grand Union Canal Carrying Company include:

London area:

Regent's Canal – original company
Hertford Union Canal – bought by the Regent's Canal in 1857

Main Line*:

Warwick and Napton Canal – bought by the Regent's Canal in 1927
Warwick and Birmingham Canal – bought by the Regent's Canal in 1927
Birmingham and Warwick Junction Canal – bought by the Regent's Canal in 1927
Grand Junction Canal – bought by the Regent's Canal in 1927

Leicester Line:

Old Grand Union Canal – bought by the Grand Junction in 1894
Leicestershire and Northamptonshire Union Canal – bought by the Grand Junction in 1894
Leicester Navigation – bought by the Grand Union in 1932
Loughborough Navigation – bought by the Grand Union in 1932
Erewash Canal – bought by the Grand Union in 1932

*The current main line starts in London and ends in Birmingham (Digbeth), stretching for 137 miles (220 km) with 166 locks.

For more details, a good start is: Link

The Leicester section branches off the main line at Braunston and it is 66 miles long with 59 locks (including two five chamber staircase locks at Foxton) and two tunnels. Near Leicester it continues into the River Soar, and briefly along the River Wreake. The navigation then proceeds along the river, with some canalised diversions, to Loughborough and the River Trent south of Long Eaton.

The River Soar is a major tributary of the River Trent and is the principal river of Leicestershire. The source of the river is midway between Hinckley and Lutterworth, it then flows north through Leicester where it is joined by the Grand Union Canal and continues through the Leicestershire Soar Valley, passing Loughborough and Kegworth, until it reaches the Trent at the county boundary. In the 18th century, the Soar was made navigable, initially between Loughborough and the Trent, and then through to Leicester. It was not until the early 19th century that it was linked by the Grand Union Canal to the wider network to the south and to London.
Wikipedia: Link