Railway Regulation (Gauge) Act 1846
The Railway Regulation (Gauge) Act was enacted by the Parliament of the United Kingdom of Great Britain and Ireland on 18 August 1846. It mandated the track gauge of to be the standard for Great Britain and 5 ft 3 in to be the standard for Ireland. The Act stipulated that "it shall not be lawful after the passing of this Act to alter the Gauge of any Railway used for the Conveyance of Passengers". It continued legislative approval of the broad-gauge constructed by the Great Western Railway engineer Isambard Kingdom Brunel, and endorsed  the construction of several new broad-gauge lines, but restricted them to the south-west of England and to Wales. The Act stated that these railways "shall be constructed on the Gauge of Seven Feet". The resulting isolation of these lines ultimately contributed to the demise of the Great Western Railway broad-gauge system.