A British company incorporated by Parliament in 1835 to…

A British company incorporated by Parliament in 1835 to link London with Bristol, nicknamed God's Wonderful Line. Its young engineer laid rails to a broad gauge of seven feet and a quarter inch, bored the Box Tunnel and designed the terminus at Paddington. Conversion of that gauge finally came in 1892. Chocolate and cream carriages, Castle and King class locomotives and the Cornish Riviera express lasted until nationalisation in 1948.

The answer in 19 letters