As authorised in 1835, the Great Western Railway extended from London to Bristol, but from the very earliest days, ambitious promoters were planning a whole series of extensions to destinations such as Birmingham, Wolverhampton, Cornwall and South Wales. These extensions were, in most cases, built by allied or subsidiary companies such as the Bristol & Exeter Railway, which, as its name suggested, ran from Bristol to Exeter, and the South Devon Railway, which continued the West of England main line from Exeter to Plymouth.

Both of these companies were subsequently absorbed into the parent GWR company, becoming, as far as ordinary travellers were concerned, an integral part of the Great Western system. Although the B&ER is an unspectacular line, the South Devon Railway runs beside estuaries and along the seashore for several miles, the waterside section between Exeter and Teignmouth being one of the most iconic parts of the British railway system.