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 October 2023, (38%) of the British rail network was electrified.Rail Infrastructure and Assets 2022-23 Annual Statistical Release Office of Rail & Road 19 October 2023
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.Network Rail, 2003 Technical Plan, Chapter 11 "Network Capability", page 7 "Electrification". "Approximately 40% of the rail network is currently equipped with electrification." From page 1, total network is 30764 km, 7587 km of 25 kV AC, 4285 km of 650/750 V DC and 28 km of 1500 V DC. Excludes CTRL, LUL, Old Danby test track, bulk of Tyne and Wear Metro, etc. NB it does not state what method of counting length of network is used - i.e. sidings, loops, double track etc. produce different numbers. The UIC statistics that are used in the chart showing electrification in Europe is based solely on line length. Thus, on this count, 11,900km (38.7%) is electrified. Of the electrified network, 63.8% is 25kV AC, 36.0% is 650/750V DC and 0.2% is 1,500V DC.
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.
Other early projects followed German practice at the time and installed AC OLE systems at a lower frequency (in this case 25Hz) than mains electricity (50–60Hz). This was initially pioneered by the Midland Railway on the short line between Lancaster, Morecambe and Heysham in 1908 using AC OLE at 6.6kV 25Hz. This was quickly followed in 1909 by a more extensive scheme in South London using similar technical standards on the suburban line between London Bridge and Victoria. Further extensions of 6.6kV OLE in South London were swiftly pursued throughout the 1910s and 1920s. However, the system was fully removed in 1929 and replaced with 660VDC third rail following the grouping of these lines into the wider Southern Railway that preferred the conductor rail system implemented by the former London and Southwestern Railway.
Wishing to avoid a repeat of the Gauge War, the Ministry of Transport commissioned inquiries into implementing a standard system for future rail electrification schemes other than London Underground lines. An advisory committee in 1921 recommended 1,500VDC for both overhead and third rail systems. This was reviewed by a committee chaired by Sir John Pringle in 1927 which revised the recommendation to 1,500VDC overhead and 750VDC third rail systems, which was formalised in legislation in 1932.The Railway (Standardisation of Electrification) Order, 1932 (SR&O 1932/827)
Post-war and Nationalisation After World War II and the nationalisation of the railways in 1948, British Railways (BR) expanded electrification at both 1,500VDC overhead and 660/750V third rail. In 1951, a British Transport Commission review of electrification generally endorsed the findings of the Pringle Committee, but additionally recommended further investigation into advances in 50Hz AC electrification. The following year, the Lancaster, Morecambe and Heysham 6.6kV 25HzAC line was experimentally converted to 50Hz. The success of this experiment, combined with the successful 25kV electrification at Aix-les-Bains, led BR in 1956 to adopt 25kV50HzAC overhead as standard for all projects outside logical extensions of third-rail systems under the Modernisation Plan, and the 1932 regulations were revoked. The Plan authorised the electrification of the West Coast Main Line as far as Manchester and Liverpool along with diversionary routes through Stoke and around Birmingham. This was a significant step in the history of British electrificationnot only for implementing new technological standards, but also in scale and scope of the work. This delivered close to 200 route miles (320km) of continuous electrified railway serving long distance and higher speed passenger services as well as significant freight traffic and several suburban lines. Up to this point the longest electrified route was between London and Portsmouth via Arundel on the third rail DC system and most electrification had been specifically for commuter and suburban traffic. Although the West Coast Main Line was the main headline for electrification under the 1955 plan, it also sanctioned other AC suburban schemes in Glasgow and North East London/South Essex that were delivered in the early 1960s as well as significant expansions of the third rail system throughout Kent and from west of Woking to Bournemouth removing steam traction.
The natural extension of the West Coast Main Line's electrification beyond Crewe through to Glasgow was authorised later in 1970 with wires meeting the Glasgow suburban network at Motherwell by 1974. However, electrification of other mainline routes languished for several decades. As well as the harsh political and economic environment for major railway investment, significant long distance electrification projects were effectively stalled by the unprecedented success of the Class 43 HST "Intercity 125" fleets that became the principle traction for intercity services on the East Coast Main Line, Great Western Main Line, Midland Main Line and Cross Country Route. This was because HST sets could deliver the same journey time benefits of electric traction without the investment of overhead line equipment. Implementation of HST trains did still require track rationalisation, line speed improvement works and re-signalling all of which had previously occurred alongside electrification schemes. Because of this, electrification projects after the completion of the West Coast Main Line were typically smaller in scope principally for suburban traffic such as London Kings Cross to Royston in 1976 and London St Pancras to Bedford in 1983.
In the mid-1980s fortunes turned in favour of electrification mostly due to the advent of sectorisation that split British Railways into business units based on the type of train service operated rather than purely geographic territories. The most major schemes authorised under the InterCity sector were electrification of the East Coast Main Line route between London and Edinburgh along with its branch to Leeds and the line between Edinburgh and Carstairs — providing an electric route between Edinburgh and Glasgow. This was despite the success of HST rolling stock in use on that route and intended to introduce capability with the new Class 91 "Intercity 225" fleet. 140mph operation was later descoped however. The project was given the go-ahead in 1984 and had delivered all work by 1991 to budget and ahead of schedule. Other notable projects in this era included large extensions of electrified lines in East Anglia with the Anglia East and Anglia West projects which, by 1987, had extended wires from Colchester to Norwich/Harwich and from Bishops Stortford to Cambridge respectively. The line north of Cambridge was further extended to King's Lynn 1992. Finally, the last major extension of the 750VDC third rail system was delivered in 1988 between Bournemouth and Weymouth.
Both the Network SouthEast and InterCity sectors were better able to justify extensions of electrification especially over minor branches and connecting lines since they were able to manage fleet allocations directly. This allowed for mid-life rolling stock to be strategically cascaded onto newly electrified lines significantly improving the business cases of those infrastructure upgrades since the trains to run electric services were essentially 'free'. This was the case especially in Network SouthEast schemes like North London Line extension to North Woolwich (1985), Crouch Valley Line (1986), Romford to Upminster (1986), Tonbridge to Hastings (1986) and the East Grinstead Line (1986), Abbey Line (1988) and St Denys/Eastleigh to Portsmouth (1990), but also on some InterCity operations like full electrification of the Great Eastern Mainline which used rolling stock previously employed on the West Coast Mainline. The only other passenger sector (Regional Railways) carried out two significant electrification projects on the Ayrshire Coast Line (1987) in Scotland and Birmingham's Cross-City line (1993).The sectors involved in freight operations were also able to further electrification goals mostly concerning the electrification of several container terminals as well as connecting lines in the London area, such as the Canonbury curve and adding 25kV onto the North London Line.
Although the schemes of this era of electrification were generally delivered on time and within cost predictions, the tight budgeting requirements often meant the electrical supply was constrained requiring follow-up projects in the late 1990s and early 2000s to add necessary resilience to the traction power system exacerbated by the continual uptick in rail travel since the 2000s. Furthermore, the overhead line system type used on these projects was designed to minimise the procurement of steel by using mostly head-span structures which have proven prone to failure in adverse weather.
Electrification following Privatisation Progress on electrification languished again after the successful delivery of the East Coast scheme pending the imminent privatisation of British Rail under the Railways Act 1993. The new privatised structure decentralised the operation of infrastructure, services, rolling stock and rolling stock procurement amongst different organisations. This meant that the financial case for new electrification was harder to make since no single organisation could benefit from the whole-system efficiencies of electric traction. This led to a large procurement of diesel rolling stock in this era. most notably the Turbostar and Voyager/Super Voyager fleets. The only notable electrification in this era were works started by British Rail and finished under Railtrack were of some suburban routes out of Leeds on the Airedale and Wharfdale lines in 1995, and the route from London Paddington to Heathrow Airport for the Heathrow Express service in 1998. Both these schemes were almost entirely developed by Regional Railways and Network SouthEast respectively. For the lines around Leeds this was in collaboration with the West Yorkshire Passenger Transport Executive, while the Heathrow Express scheme was largely funded by the British Airports Authority.