Through the 19th century, railway competition increasingly reduced canal profitability.  In the early 20th century, especially in the years following the Great War, the lorry became the greatest threat. During the late 1920's, the Regent's Canal and the Grand Junction Canal Companies agreed that amalgamation to a much larger concern was the only way to remain competitive.

 

Following an Act of Parliament in August 1928, the Grand Union Canal Company came into existence on 1st January 1929 combining the Regents Canal, the Grand Junction Canal, the Warwick and Napton Canal, the Warwick and Birmingham Canal and the Birmingham and Warwick Junction Canal. This new entity had a through line from London to both Birmingham (although the stretch from Braunston to Napton remained with the Oxford Canal) and to Leicester. In 1932, the Leicester navigation, Loughborough Navigation and Erewash Canal were purchased by the Grand Union to extend its Leicester Line right into the Derbyshire/Nottinghamshire coalfields.

 

The Grand Union Canal Company was nationalised in 1948, with control transferring to the British Transport Commission (Waterways) , then in 1962 to the British Waterways Board, later British Waterways. Commercial traffic continued to decline, effectively ceasing in the 1970s.