The Midland main line from London St Pancras to the north of England is one of Britain's most important trunk routes. With its various loops and branches, this major artery of communication links busy centres of population such as Leicester, Derby, Nottingham, Sheffield, Manchester and Leeds. Notwithstanding its obvious importance as a busy main line, the Midland route was built in piecemeal fashion, the various sections (from London northwards) being the Midland Railway London Extension (opened 1868); the Leicester & Hitchen Railway (1857); the Midland Counties Railway (1840); and the North Midland Railway (1840). In recent years the Midland line has been regarded primarily as a link between London and Sheffield, although a number of services have continued to run through to Leeds, Manchester and other destinations in the north of England. However, during the Midland Railway period the best trains had run northward beyond Leeds, and thence along the spectacular Settle & Carlisle route which, in turn, provided a direct link to Scotland via the Glasgow & South Western Railway. Prestigious Anglo-Scottish trains no longer run on the Midland main line, but this historic route remains in operation as a vital part of the national railway system.

Formed in 1864 by the amalgamation of the Oswestry & Newtown, Newtown & Machynlleth, Llanidloes & Newtown and several other railway companies, Cambrian Railways was the largest independent railway in Wales, with a long, winding, single-track main line that extended from Whitchurch in the east to Aberystwyth and Pwllheli on the Welsh coast. In 1922, the company was amalgamated with the Great Western Railway under the provisions of the Railways Act 1921 and thereafter, the Cambrian line was worked as an integral part of the GWR system. The present-day Cambrian main line runs from Shrewsbury to Pwllheli, a distance of 1183/4 miles, and there is an important branch to Aberystwyth. The line, which runs through spectacular mountain and coastal scenery, serves as a vital lifeline for the inhabitants of scattered towns and villages such as Welshpool, Machynlleth and Harlech, while at the same time the sinuous Cambrian route plays an important role in the Welsh tourist industry - a role that is further enhanced by the way in which this highly scenic route provides a convenient link between several of the famous Welsh 'heritage' railways.