The Class 158 units were built by BREL at Derby betweeen 1989 and 1992. They mainly replaced loco-hauled passenger trains, and the life-expired heritage DMUs. The Class 158s have a large amount of similarities to the Class 159, as the latter was converted from excess Class 158s.

In total, 182 units were built, mostly as 2 car sets, however some are in a 3 car formation, including the hybrid units in use with Great Western Railway, which use a spare driving cars as intermediate carriages.

The units can work with Class 150s, Class 153s, Class 155s, Class 156s, Class 159s, Class 170s, and Class 172s. They cannot work with Class 165s or Class 166s, due to incompatible wiring.