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 25 kV AC using overhead lines, and the 750 V DC third rail system used in Southeast England and on Merseyrail.

In 2026, English trains are powered by a mix of electricity, diesel, and emerging green technologies. Roughly 38% to 45% of the UK rail network is electrified. These electric trains receive power either through overhead catenary lines (25kV AC), common on main lines like the West Coast and East Coast Main Lines, or via a "third rail" (750V DC), which is prevalent in London and the Southeast. Many of the newer "Bi-mode" trains, like the Hitachi Class 800, can switch seamlessly between overhead electric power and onboard diesel engines for sections of the track that aren't yet electrified. Additionally, 2026 has seen a significant push toward Battery-Electric and Hydrogen power for shorter, rural branch lines where electrification is too expensive. Older rolling stock still relies on diesel-mechanical or diesel-electric power, where a diesel engine turns a generator to drive electric motors. The government's goal is to remove all "diesel-only" trains by 2040, making the current era a "transition period" dominated by high-speed electric units and more efficient hybrid technology.