The BPRP ran into trouble by 1871 when the terminal pier at Avonmouth became difficult to use due to a build-up of silt. With no prospect of a proper dock being funded without a connection to the national rail network, the Clifton Extension Railway (CER) was approved. This was a joint venture by the BPRP, Great Western Railway and Midland Railway which ran from Sneyd Park Junction, south of Sea Mills, via , to join up with the national network at Narroways Hill Junction. The link opened in 1877, but only for goods trains: Colonel William Yolland, the chief inspector of British railways, considered the platforms at Sea Mills to be too short for passenger interchange, as they were shorter than at any station on the CER. Rather than build a new interchange station at Sneyd Park Junction, the platforms at Sea Mills were extended to at the expense of the BPRP. The goods siding was also removed at this time, as Yolland had expressed concern that the points were not interlocked. The route from Sneyd Park Junction to Clifton Down was subsequently cleared for passenger use on 3 August 1878, but the Midland and Great Western Railways did not think the BPRP track was in a suitable condition and so refused to run any passenger trains beyond Clifton Down. Services along the BPRP however increased to eight trains per day in each direction from 1877, and then to ten each way by 1887. From 1 September 1885, when passenger services along the link finally started, the Great Western offered six trains per day each direction between and . Fearing competition, the BPRP did not allow passengers to use GWR services between its stations. The Midland Railway did not run any passenger services beyond Clifton Down, apart from a one-month trial service in September 1885. Despite the increased traffic, the BPRP suffered financially, and was taken over by the CER in 1890.