Formerly it ran for around 6 miles (9.7 km) from the Great Western Main Line at West Drayton to Staines-upon-Thames in Surrey, passing through the village of Colnbrook in Berkshire.

The operational part of the line, north of Colnbrook, runs for 2 mi 74 ch (4.7 km) and is used exclusively by freight trains.

The earliest plans for a railway linking Staines-upon-Thames to the Great Western Main Line were put forward in the 1840s, but were not approved by parliament at the time.

The line from West Drayton to Colnbrook opened on 9 August 1884 and passenger services began running to Staines-upon-Thames on 2 November 1885.

The full length of the line remained open for freight trains, until the southern half was closed in 1981 to allow the construction of the M25 motorway.

The operational part of the line runs for 2 mi 74 ch (4.7 km) from West Drayton Junction to Colnbrook Oil Terminal.

It branches from the northern side of the GWML, 13 mi 31 ch (21.5 km) west of London Paddington, and immediately turns southwards, descending on a 1 in 104 gradient to pass beneath the main line.

[3] The single-track line has a maximum speed limit of 20 mph (32 km/h) and train movements are controlled from Thames Valley Signalling Centre.

The Great Western Railway (GWR) agreed to operate passenger services, but the powers to construct the line expired before sufficient capital could be raised.

In 1882, the S&WDR submitted a second bill in November 1882, to allow it to develop its own station in Staines-upon-Thames and to build a link to the linoleum factory in the town.

[11] The line from West Drayton to Colnbrook opened on 9 August 1884 and passenger services began running to Staines-upon-Thames on 2 November 1885.

[3] Although goods yards were provided at both Colnbrook and Staines West from opening, freight traffic on the line was slow to develop.

[5] In May 1877, a link was built across the River Colne to allow GWR trains to access the goods yard for the Staines Linoleum Works, a facility shared with the LSWR.

[15][23] On 24 June 1964, Shell-Mex and BP opened a rail terminal for heating oil on the site of the former Staines West goods yard.

[29] In January 2022, GB Railfreight began hauling aggregates trains to Thorney Mill from Newhaven[30] and a five-year expansion plan to increase the site capacity to 26 freight wagons was announced in August 2024.

[3] The proposed Airtrack-Lite rail link from Heathrow Airport through Staines-upon-Thames would entail laying track near the former southern part of the S&WDR route.