the southern leg of a longer distance route to , and Birkenhead. It ran via the Great Western Main Line to and then via , and . This route was circuitous, and was longer between London and Birmingham than the rival London and North Western Railway's Euston-New Street route via , meaning that the GWR could not compete on journey times. The second phase was completed in 1906: In order to create a more direct route, the GWR collaborated with the Great Central Railway (GCR) to create a new railway known as the Great Western and Great Central Joint Railway between Northolt (in north west London) and Ashendon Junction (west of Aylesbury) via . Thirdly, as a final development, the GWR opened the Bicester cut-off line in 1910: this was an connection between the Great Western and Great Central Joint Railway at Ashendon Junction, via , to Aynho Junction on the Birmingham line south of Banbury. This shortened the route between London and Birmingham by compared to the original Oxford route, and reduced the fastest London-Birmingham journey times by 20 minutes (from 140 to 120 minutes); most of the through trains were immediately transferred to the new route, although the original route via Oxford continued in use, and is now known as the Cherwell Valley line. Heyday, decline and rationalisation During the heyday of the route, many prestigious trains ran from Paddington to the northwest of England via the Joint Line, reaching Wolverhampton, , , and . Various through services from Marylebone to the GCR network also ran via the Joint Line between London and Ashendon Junction. At nationalisation in 1948, the line passed to the Western Region of British Railways, which continued to operate Paddington – Birmingham – Wolverhampton - Birkenhead fast trains through the 1950s in competition with the London Midland Region's (LMR) from via the West Coast Main Line (WCML). The Paddington – Birmingham – Wolverhampton - Birkenhead fast service was sharply increased in frequency to up to 15 trains a day each way from the 1959–60 timetable to compensate for the withdrawal of most LMR trains during electrification of the WCML. For the same reason, the Chiltern line was used by many trains between Paddington and Birkenhead from 1965. All local trains were diverted to Marylebone in 1963 and operated by four-car Class 115 DMUs, and the main-line platforms at Greenford on the New North route