 Following Watkin 's retirement relations between the GCR and the MR deteriorated badly . The GCR route to London ran over the MR from Quainton Road to London , and to reduce reliance on the hostile MR , GCR General Manager William Pollitt decided to create a link with the Great Western Railway and a route into London that bypassed the MR. In 1899 the Great Western and Great Central Joint Railway began construction of a new line , commonly known as the Alternative Route , to link the GWR at Princes Risborough to the GCR at Grendon Underwood , about three miles ( 5 km ) north of Quainton Road . Although formally an independent company , the new line was operated as a part of the GCR . A substantial part of GCR traffic to and from London was diverted onto the Alternative Route , reducing the significance of Quainton Road as an interchange and damaging the profitability of the MR. 
