The re-signalling of 1000 track miles from the River Weaver to the Clyde brings the whole line from London to Glasgow under one system of push-button control and colour light signals, and completes 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.

• British Transport Films
• Gary Watson