The West London Railway was conceived to link the London and Birmingham Railway and the Great Western Railway with the Kensington Basin of the Kensington Canal, enabling access to and from London docks for the carriage of goods. It opened in 1844 but was not commercially successful.
In 1863 the canal was closed and the railway extended southwards on its alignment as the West London Extension Railway, crossing the River Thames on a new bridge and connecting with the London Brighton and South Coast Railway and the London and South Western Railway south of the Thames. Local and long-distance passenger traffic was carried, and goods traffic exchanging between the connected railways. Passenger traffic declined after 1940, but the line remained open for sporadic freight services. In recent years regular local passenger services have revived the traffic on the line.
The short "Kensington Canal" was opened on 12 August 1828, running from the River Thames a little west of Battersea Bridge to a basin near Kensington Road and Uxbridge Road, in a relatively undeveloped area to the west of London. The Times reported that "the canal runs from the Thames, near the Battersea-bridge, directly north two miles and a quarter, terminating close to the great Western road."
It had been intended that the canal would be extended further north to the Grand Junction Canal but the cost of the section built was much more than estimated. The canal was tidal, like the Thames, and the traffic and income from it were substantially less than hoped for, and the extension was dropped.
The London and Birmingham Railway and the Great Western Railway were projected in the early 1830s. Their London terminals would be on the north-west margin of London, and at that time they considered it essential to have a connection to the London docks east of London Bridge: a railway to a canal connected with the Thames might serve this purpose. In February 1836 the canal proprietors accepted an offer for their canal from the new "Birmingham, Bristol and Thames Junction Railway".
The railway company obtained an Act of Parliament on 21 June 1836 authorising it to build a railway from Holsden Green (later called Harlesden), under the Paddington Canal at Wormholt Scrubbs (later Wormwood Scrubs), under the Uxbridge Road (then the Oxford Road) and under the Hammersmith Turnpike.
Construction of the line was much delayed, and meanwhile the Great Western Railway (GWR) was being built across its path. A flat crossing was arranged, and by agreement of 4 February 1837 GWR trains would have precedence with signals and heavy barriers across the BB&TJR line provided under the control of a GWR man.