The Great Western & Great Central Joint Committee was created with the dual objective of providing the Great Central Railway with a second route into London, bypassing the Metropolitan Railway; and of providing the GWR with a shorter route to the Midlands. Central to this scheme was the upgrading of the existing GWR route between and Princes Risborough, which was transferred to the Joint Committee at its establishment on 1 August 1899. The line was extended in a north-westerly direction to Ashendon Junction, at which point the joint line ended, and a GCR route ran northwards to Grendon Underwood Junction, just south of ; both sections opened for goods on 20 November 1905, and for passengers on 2 April 1906. Continuing in the same north-westerly direction from Ashendon Junction, the Bicester cut-off line, which was purely GWR property, was opened for goods trains on 4 April 1910, and to passengers on 1 July 1910.