They were a variant of British Rail's standard 1972 design for suburban EMUs, eventually encompassing 755 vehicles and five classes (313/314/315/507/508).

Following planning and building, British Rail diverted the 508s to work alongside much older first-generation 4Sub EMUs in the London Waterloo area.

[7] Based at Wimbledon Traincare Depot, they soon became problematic due to their non-standard dimensions and brake problems caused by leaf fall.

[16] They were refurbished at Eastleigh Works, including the installation of 2+2 seating and wheel-in cycle racks in the centre cars, and reclassified as the Class 508/2 (508201-212).

In 2005, one unit was refurbished by interim operator South Eastern Trains to improve external appearances, with a black, white and yellow livery.

[citation needed] In September 2006 new operator Southeastern announced that a cascade of rolling stock would see Class 466 units replace the 508s on the Sheerness and Medway Valley lines in the December 2006 timetable.

With the transfer of the Tonbridge to London via Redhill services to Southern, Southeastern placed its remaining Class 508 units in store in December 2008.

[19] Network Rail's Route Utilisation Strategy for Merseyside has called for an expansion to Merseyrail's current fleet to allow for both additional services and lengthening of trains to six cars.

As part of the agreement with Angel Trains, the fleet received a refresh package including external re-livery, internal enhancements and engineering work.

[29] On 6 March 2007, a Class 508/3 unit, forming the 05:00 Tonbridge to Gatwick Airport, derailed near Crowhurst, Surrey, after hitting a fallen tree on the line.