Following experience gained with the first batch of railcars built to a lightweight design from aluminium and completed in 1954/55 Derby Works developed a range of low density sets to a roughly similar design but with steel, rather than aluminium ends to improve strength.
Each power car had two Leyland 150bhp 680 engines with standard mechanical drive and wighed only 29 tons, despite providing seating for 52 people and accomodation for the guard and luggage.
A large number of what became known as the Class 108 vehicles were built and 51907 was one of the final batch of 29 sets, which were different to the rest in that they had the large headcode box on the roof to house the four-character headcode box.

Delivered to the London Midland Region this car was allocated new, along with its current partner M54490, in April 1960 to Toton (probably only on paper).It was shown as being transferred to Trafford Park in 1962 and then Longsight Depot in Manchester by 1963 where it remained for the bulk of its working life, except for a few years when it was transferred to and worked from Chester Depot. It was back at Longsight for its final years and was withdrawn from there in 1993 . The unit was inspected, along with many others, for further use at Llangollen and was selected for preservation due to its good overall condition, having been through Doncaster Works as late as 1990. Once delivered by lorry it was put straight into service. It was partially refurbished upon arrival, including the fitting of replacement seats and received a full body overhaul, repaint and a replacement number one engine in 1999.

Since arriving at Llangollen 51907 has worked for every season and has now notched up an impressive 25,000 miles in service between Llangollen and Carrog. It formed the first train over the Glyndyfrdwy to Carrog section when that opened and is often used on off-peak weekend trains and during gala events. The lightweight design ensures that the Class 108 is economical on fuel.

This vehicle is preserved in its later refurbished form and is fitted with strip lighting, a brighter Formica interior, additional engine silencing and other electrical and mechanical modifications, which were applied during the years the class was in service. It is painted in the British Railways blue and grey livery applied  from around 1970 onwards, prior to this it would have been plain blue and before that green.

On the Llangollen Railway this vehicle was originally based at Glyndyfrdwy stabling point but was transferred to Pentrefelin Depot, along with the rest of the railcar fleet, when Glyndyfrdwy was closed in 2005.
It has recently has had a completely refurbished first class interior fitted and has also been fitted with public address equipment which is used both for scenic tours of the railway and for educational tours for Welsh language learners.