Railway electrification in Great Britain began in the late 19th century. A range of voltages has been used, employing both overhead lines and conductor rails. The two most common systems are using overhead lines, and the third rail system used in Southeast England and on Merseyrail. As of March 2020, (38%) of the British rail network was electrified. According to Network Rail, as at 2003, 64% of the electrified network used the 25kVAC overhead system, and 36% used the 660/750VDC third-rail system. The electrified network is set to expand over coming years, as 25kV electrification is extended to currently unelectrified lines such as the Midland Main Line, as well as lines in the North of England as part of the Northern Hub. History Early electrification The first electric railway in Great Britain was Volk's Electric Railway in Brighton, a pleasure railway, which opened in 1883, still functioning to this day. The London Underground began operating electric services using a fourth rail system in 1890 on the City and South London Railway, now part of the London Underground Northern line. The Liverpool Overhead Railway followed in 1893, being designed from the outset to be electric traction, unlike the City and South London Railway which was designed to be cable hauled initially. Main line electrification of some suburban lines began in the early years of the 20th century, using a variety of different systems. The Mersey Railway converted to 600VDC electric multiple-unit operation on 3 May 1903, thus eliminating the problems caused by steam traction in the long tunnel under the River Mersey, and the Lancashire & Yorkshire Railway's Liverpool Exchange to Southport (and on to Crossens) suburban commuter line was similarly electrified at 625V by March 1904. Both of these lines initially used a fourth rail system. In 1921, a government committee chose 1,500VDC overhead to be the national standard, but little implementation followed and many different systems co-existed. During the interwar period, the Southern Railway adopted the 660VDC third rail system as its standard and greatly expanded this system across its network of lines South of London. Post-war After World War II and the nationalisation of the railways in 1948, British Railways (BR) expanded electrification at both 1,500VDC overhead and 660/750 V third rail. In 1956, BR adopted 25 kV AC overhead as standard for all projects outside logical extensions of third-rail systems. Twenty-first century The 25kVAC network has continued