The GWR had originally intended to use the Thame route to reach Oxford from Princes Risborough by upgrading the former Wycombe Railway route. This was however considered a roundabout route and the GWR now decided to build a mile direct link from further north on the GCR part of the new line to Banbury. A junction was to be made at Ashendon, between Princes Risborough and Grendon Underwood, and this GWR section of line would join the Oxford to Banbury line at a new junction at Aynho, not far south of Banbury. Under this revision, the actual joint section of the new construction was from Northolt Junction to Ashendon Junction, a distance of 34 miles, but the scheme involved a total of miles of new double track: the last major new railway construction in Great Britain until the Channel Tunnel Rail Link of 2003.