This vintage railway film, produced by British Transport Films in 1974, documents the re-signalling of 1000 track miles from the River Weaver to the Clyde, bringing the whole line from London to Glasgow under one system of push-button control and colour light signals and completing the main line electrification.

The film follows the intricate production of equipment, and its installation over, under and between trains. The whole project adds up to a piece of modern technology unsurpassed anywhere in the world.