The designation Class 43 has been used more than once under the British Rail TOPS classification system. Today the number is most commonly associated with the power cars of the InterCity 125 High Speed Train (HST), but historically the same class number was applied earlier to a small, now-obsolete group of locomotives.

InterCity 125 HST power cars

The best-known Class 43 machines are the diesel power cars built to form the bookends of InterCity 125 trainsets introduced in the mid-1970s. These vehicles were designed as high-speed motive power for fixed-formation express sets and became the backbone of long-distance passenger services in Britain for decades. Each trainset normally carries two power cars, one at each end, and the combination of aerodynamic bodywork and high-power diesel engines allowed sustained high-speed running on conventional track.

Characteristics and typical modifications

  • Configured as single-cab power cars that operate with sets of coaches rather than as independent locomotives.
  • Originally fitted with high-speed diesel engines; many units were re-engined or refurbished during later overhauls to improve reliability and emissions.
  • Capable of high-speed express operation and widely used on inter-city routes across the network.

Earlier allocation

Before the HST power cars became synonymous with Class 43, the number was briefly allocated to an earlier family of locomotives under TOPS. That initial use applied to a small, regionally used group whose allocation has since been retired or renumbered. The re-use of class numbers is not uncommon in the TOPS scheme and reflects changing fleets and retirements.

Importance and legacy

The HST-era Class 43 power cars had a major impact on British passenger rail by raising average journey speeds and offering reliable, high-capacity services without electrification. Over time many units were refurbished, re-engined and repainted by successive operators; others have been preserved on heritage railways. For background on the wider organisational context of these classifications see British Rail.

Notable distinctions: in common usage "Class 43" usually refers specifically to the HST power cars rather than the entire trainset or the coaching stock. The number therefore denotes the individual powered vehicle within a fixed formation rather than the complete train.