A compilation of Pacers featuring Class 141 Class 142 Class 143 and Class 144. filmed between 2014 and 2019

Pacer is the operational name of the British Rail Classes 140, 141, 142, 143 and 144 diesel multiple unit railbuses, built between 1980 and 1987. The railbuses were intended as a short-term solution to a shortage of rolling stock, with a lifespan of no more than 20 years.

All Pacer trains were scheduled to be retired by the end of 2019 as the Rail Vehicle Accessibility Regulations require that all public passenger trains must be accessible to disabled people by 2020 - however the Pacer units were given dispensation until the end of 2020. Only one Pacer (the modernised 144e) currently meets this requirement, and the remainder were therefore planned to be withdrawn by that date. Furthermore, a decision in 2015 by the Transport Secretary required that such railbuses be removed from service by 2020 for the then-new Northern franchise, stating that the "continued use of these uncomfortable and low-quality vehicles is not compatible with our vision for economic growth and prosperity in the north".

At the start of 2020, 138 Pacer units were either still in service or storage with three National Rail operators: Northern Trains, Great Western Railway and Transport for Wales. Northern Trains retired its last Pacer unit on 27 November 2020, with Great Western Railway and Transport for Wales expected to follow by the end of the year.