The British Rail Class 143 is a diesel multiple unit railbus, part of the Pacer family of passenger trains introduced between 1985 and 1986.

During the 1980s, British Rail (BR) was interested in replacing its first-generation diesel multiple units, particularly in the use of railbuses to service its lightly used branch lines. It was decided to develop such a vehicle with a high level of commonality with the widely used Leyland National bus, leading to its modular design serving as the basis for the design. Several single and two-car prototypes were constructed and evaluated, leading to an initial production batch by British Leyland, designated as the Class 141 units. BR, seeking to procure improved derivatives of the Class 141, placed an order with the manufacturers Hunslet-Barclay and Walter Alexander to construct its own variant, the Class 143.

Entering operational service during the mid-1980s, the Class 143 embodied several advances over the original model in terms of ride quality and reliability. During its operating lives, the type was tasked with various passenger services across the United Kingdom; being initially operated in the North-East of England, all units were subsequently transferred to other regions, including Wales and South-West England.