By the beginning of the 1980s, British Rail (BR) was operating a large fleet of first-generation DMUs of various designs.

[14] While formulating its long-term strategy for this sector of its operations, BR planners recognised that there would be considerable costs incurred by undertaking refurbishment programmes necessary for the continued use of these ageing multiple units, particularly due to the necessity of handling and removing hazardous materials such as asbestos.

[11] In the concept stage, two separate approaches were devised, one involving a so-called railbus that prioritised the minimisation of both initial (procurement) and ongoing (maintenance and operational) costs, while the second was a more substantial DMU that could deliver better performance than the existing fleet, particularly on long-distance services.

[11] The initial specification developed for the latter type was relatively ambitious for the era, calling for a maximum speed of 90 mph (140 km/h), a rate of acceleration comparable to contemporary EMUs, the ability to couple/work in multiple with existing EMUs, facilitate through-access for passengers, feature pressure ventilation, the ability to assist another failed unit, and to comprise either a three or four-car consist.

[11] This specification led to the development of the experimental British Rail Class 210 diesel-electric multiple unit.

However, to deliver the performance specified, it was found that relatively expensive equipment had to be used, particularly to provide sufficient speed, acceleration, and through-passenger access; it also had maintainability problems due to space limitations.

Despite these shortcomings, it was recognised that a production fleet that was assembled from proven components would possess both a greater reliability level and lower maintenance costs; it was forecast to achieve an availability rate of 85 percent.

[11] Specifically, it was decided to lower the top speed from 90 to 75 mph (145 to 121 km/h), as testing had shown that the higher rate brought no perceptible improvement in journey times due to the typically short distances between the stations that the type was intended to serve.

[11] From an operational perspective, it was intended that the DMU could be assembled akin to building blocks, comprising between two and four cars that may or may not be outfitted with various passenger amenities such as toilets and luggage spaces.

[11] As part of this process, these manufacturers submitted bids to construct an initial series of three-car prototypes as demonstration units.

A relatively constrained timetable of 18 months from the date of order to delivery of these prototypes was also specified; this has been blamed for restricting manufacturers to existing industrial practices for their submissions.

The bid submitted by British Rail Engineering Limited (BREL) was heavily based on its successful Class 455 EMU, sharing its body and the majority of its running gear, albeit equipped with two different power trains.

The railway engineering company Metro-Cammell also bid, offering its own design that employed rivetted aluminium construction; this feature was credited with enabling a meaningful reduction in weight over conventional methods.

[11] BR officials quickly opted to proceed with a pair of prototypes from both BREL and Metro-Cammell, issuing orders to these manufacturers thenceforth.

In common with other non-intercity stock of the time, the trains lack air conditioning, ventilation being provided though opening hopper windows.

These tests revealed that the Class 150 had exceptional ride quality, as well as fully meeting the 50 percent engine-out performance requirements.

Originally based at Derby Etches Park depot, these units were introduced in 1985,[17] mainly concentrated around Birmingham and Manchester, and in later years restricted mainly to commuter services.

This also gave the operational advantage of there being an extra set of passenger door controls within the train for use by the conductor, making it easier to collect revenue without having to run the full length of the unit between stations.

[citation needed] During the 2000s, these blue buttons were replaced across the fleet by the standard EAO series 56 'easy to see, easy to press' raised circular door button, with braille writing for the visually impaired, over a yellow surround to comply with the Rail Vehicle Accessibility Regulations.

Great Western Railway currently operates a fleet of 20 Class 150/2 units which are mainly used for services on the local branch lines in Devon.

The units transferred to Arriva Trains Wales in December 2003, with more later acquired for the reopened Ebbw Vale line.

Following privatisation of British Rail, both Silverlink and Central Trains operated Class 150s in the midland regions of England and both companies were run by National Express.

[citation needed] In July 2023, three Class 150/1s, 150137, 150139 and 150141, were transferred from Northern Trains to London Northwestern Railway for use on the Marston Vale line, after the Class 230s in use on the line were withdrawn from use in December 2022 due to maintenance concerns after the company who maintained the units, Vivarail, went into administration.

Other workings included Dundee and Carnoustie, as well as operating alongside other DMUs such as Class 158s on the services between Newcraighall through Edinburgh to Bathgate, Stirling, Dunblane and occasionally Perth.

[27] Anglia Railways was created upon privatisation of British Rail, and it initially inherited a small fleet of nine Class 150/2 units, later supplemented with a tenth.

[citation needed] Anglia Railways named all bar one unit (150245) of its fleet after famous local figures.

[28][failed verification] The majority of the names are references to the Marston Vale Line on which they operated during Silverlink's franchise: Leslie Crabbe was a long-standing railway employee, who worked on the route; Richard Crane is the chairman of the Bletchley to Bedford Rail Users Association who has campaigned for the line to be retained and expanded.