One hundred and fifty-one were built at Derby, Crewe and Darlington, the first twenty of them as part of the British Railways 1955 Modernisation Plan.

The diesel engine powered another off-the-shelf product, the British Thomson-Houston (BTH) RTB15656 main generator which, in the class 24, was rated at 735 kW (986 hp), 750/525 V and 980/1400 A at 750 rpm.

The following ten locos had the similar 1,750 pounds (790 kg) per hour type OK4616B and a reduced water capacity of 450 imperial gallons (2,000 litres; 540 US gallons), and this was perpetuated in the remaining production run which used the Stone Vapour 1,000 pounds (450 kg) per hour type L4610 boiler.

Also very visible were the roof-mounted headcode boxes fitted from D5114 giving an outward appearance very similar to the later Class 25 but without horn grilles.

The pilot scheme locomotives were delivered in overall green livery with a grey roof and black below the body.

These were after-market car headlamps mounted in the plated-over nose doors, to provide extra visibility to users of level crossings on sharply curved branch lines.

[citation needed] In 1960 D5008 was fitted with a Pressure-charging Protection Unit which was designed to prevent the engine from running continuously above the smoke limit.

Class 24s took over the 'Condor' fast freight service between London (Hendon) and Glasgow (Gushetfaulds) in 1961, the train having previously been hauled by the Metro-Vic Co-Bo locos for which it is best remembered.

Thus the class was also used when a second "Condor" fast overnight freight service was introduced, running from Aston to Glasgow.

[11] The batch D5096–D5113 were all allocated to Gateshead depot in 1966 to replace 9F steam locos on the Tyne Dock to Consett iron ore trains.

These workings, typically with loads of around 1,000 tons, were double-headed and continued until taken over by Class 37s in the 1970s, when these locos were reallocated to Scottish depots.

Incidentally D5096 was, when delivered in January 1960, the first main line diesel locomotive to be built at Darlington Works.

[14] This proved to be an issue on summer Saturdays, and after problems with timekeeping and failures in service, heavier trains were double-headed or hauled by the more powerful Class 40 locomotives between Shrewsbury and Aberystwyth.

[15] In November 1975, 24061 was transferred to BRs research department based at Derby Works, and was allocated the number RDB968007.

[12] This loco was subsequently renumbered as 97201 and was finally withdrawn on 4 December 1987,[citation needed] the last Class 24 to be operational on BR.

[16][17][18] The very first Class 24 to be withdrawn was in November 1967 when a fire broke out on D5051 while it was working a train of empty coal wagons in Scotland.

In this case D5122, running light engine, hit a stationary DMU at about 40 mph (64 km/h), the impact and subsequent fire bending the main frames and completely destroying the No.2 end.

[23] The final recorded passenger duty of a Class 24 was on 2 August 1979 when 24081 rescued 40129 at Colwyn Bay on the 18:05 Holyhead – Euston, hauling the train as far as Crewe.

[12][31] This loco, allocated to Crewe Diesel Depot had been considered something of a celebrity, lasting over a year after the previous withdrawal of 24063 on 9 April 1979.