The InterCity 125 was built between 1975 and 1982 at BREL Crewe Works. A total of 197 power cars were produced allowing for up to 98 sets of the train.

The trains have a top speed of 125mph in service, but on trial runs have reached up to 148mph making them the fastest diesel train in the world. Since setting this record, the trains have been celebrated all across the United Kingdom serving the long-distance services out of London Paddington, London Euston, London Kings Cross, and London St Pancras.

The fifty-eight sets in use with Great Western Railway currently operate between London Paddington and along the GWML and beyond as far west as Penzance. They are currently set to be replaced by Class 800, 801 and 802 trains.