Until the West Coast Main Line was electrified in the mid-1960s, there was a second main line from London to Birmingham. This was the Great Western Route which was originally very indirect and ran via Oxford. In its last years, it diverged from the main Great Western line at Old Oak Common and ran parallel to the Central Line as far as Ruislip. The line from Marylebone joined it at Northolt Junction, and from there northwards through High Wycombe to beyond Princes Risborough it was a joint Great Western and Great Central (later LNER) route. The section from Old Oak Common to South Ruislip, which has been selected as part of the new High Speed 2 route, is not at present used for passenger services.
At Ashendon Junction north of Princes Risborough, there was a connection to the main Great Central main line at Grendon Underwood. The line crosses over the mothballed Oxford to Cambridge Line at Bicester, with a station at Bicester North, and rejoins the original Oxford to Birmingham line at Aynho Junction south of Banbury. From there it continues, at one time as a four-track main line, to Leamington, Warwick, Solihull and Birmingham Snow Hill. The latter station is still open, though much reduced in size. Much of the site is occupied by a car park. A single line route provides a connection between Leamington and Coventry.
The line has recently been upgraded, with double track from Northolt Junction to Aynho. A new service now runs from Marylebone to Wrexham. Plans are in hand to add a spur at Bicester to enable Chiltern Railways to run a service to Oxford. There is no firm´proposal to electrify this increasingly busy route.