In the early days of privatisation, the Class 158 Express Sprinter units were in regular use by Wales & West on its long-distance Alphaline services from South Wales to North-West England, North Wales, Cornwall and London Waterloo, as well as on some Central Trains services to Cardiff Central and along the Cambrian Line.
Successor companies Wales & Borders (2001) and Arriva Trains Wales (2003) continued to use this type of unit on similar workings, with a total allocation of 40 units also allowing Cambrian Line services to become entirely Class 158-operated.
By the end of 2006, a total of 16 units (158815-158817 and 158842-158854) had returned to the leasing company as Arriva gained exclusive use of the entire Class 175 Coradia fleet which had previously been shared with other train operators.

The remaining 24-strong Class 158 Express Sprinter fleet became permanently based at a purpose-built depot in Machynlleth during 2007.
Despite initial problems in retro-fitting the necessary 'glass cockpit'-style driver controls, Arriva's Class 158 Express Sprinter units became the first fleet in the UK to be equipped for regular use with the ETCS Level 2 signalling system.
Commercial operation under ETCS started on 28 March 2011.

Accordingly, the units operate all Cambrian Line services between Mid Wales and Birmingham, as well as supplementing the Class 175 Coradia units on other long-distance routes.
In 2009, Arriva also proposed using the fleet to provide a direct service between Aberystwyth and London, although this proposal was later rejected by the Office of Rail Regulation.

A complete refurbishment programme to provide the Class 158s with full 'as new' interiors took place between December 2010 and October 2012.
Funded by the Welsh Assembly Government at a cost of £7.5m, work completed included interior and exterior repainting, along with replacement of seating, wall coverings, carpets, lighting, luggage racks and toilet fittings.
A passenger information system has been fitted, while selected seats gained at-seat power sockets for mobile phones and laptops.

Until this refurbishment, the fleet had seen only minor attention to its interior since a refit by Wales & West in the late 1990s (little more than the fabric on the older seats changed and CCTV fitted) as well as having been only partially repainted into Arriva colours externally.
The door controls and exterior destination displays did start to be replaced before the major refurbishment.

WiFi was fitted in 2017, and Persons with Reduced Mobility modifications began in June 2018, with toilet retention tanks also being fitted.
On 14 October 2018, these units transferred to Transport for Wales.
In February 2019, the first unit was seen in Transport for Wales colours.
These are set to be replaced by 2023 alongside the rest of the Transport for Wales fleet by a total of 77 Class 197 units.
In the early days of privatisation, the Class 158 Express Sprinter units were in regular use by Wales & West on its long-distance Alphaline services from South Wales to North-West England, North Wales, Cornwall and London Waterloo, as well as on some Central Trains services to Cardiff Central and along the Cambrian Line. Successor companies Wales & Borders (2001) and Arriva Trains Wales (2003) continued to use this type of unit on similar workings, with a total allocation of 40 units also allowing Cambrian Line services to become entirely Class 158-operated. By the end of 2006, a total of 16 units (158815-158817 and 158842-158854) had returned to the leasing company as Arriva gained exclusive use of the entire Class 175 Coradia fleet which had previously been shared with other train operators.
The remaining 24-strong Class 158 Express Sprinter fleet became permanently based at a purpose-built depot in Machynlleth during 2007. Despite initial problems in retro-fitting the necessary 'glass cockpit'-style driver controls, Arriva's Class 158 Express Sprinter units became the first fleet in the UK to be equipped for regular use with the ETCS Level 2 signalling system. Commercial operation under ETCS started on 28 March 2011.
Accordingly, the units operate all Cambrian Line services between Mid Wales and Birmingham, as well as supplementing the Class 175 Coradia units on other long-distance routes. In 2009, Arriva also proposed using the fleet to provide a direct service between Aberystwyth and London, although this proposal was later rejected by the Office of Rail Regulation.
A complete refurbishment programme to provide the Class 158s with full 'as new' interiors took place between December 2010 and October 2012. Funded by the Welsh Assembly Government at a cost of £7.5m, work completed included interior and exterior repainting, along with replacement of seating, wall coverings, carpets, lighting, luggage racks and toilet fittings. A passenger information system has been fitted, while selected seats gained at-seat power sockets for mobile phones and laptops.
Until this refurbishment, the fleet had seen only minor attention to its interior since a refit by Wales & West in the late 1990s (little more than the fabric on the older seats changed and CCTV fitted) as well as having been only partially repainted into Arriva colours externally. The door controls and exterior destination displays did start to be replaced before the major refurbishment. 
WiFi was fitted in 2017, and Persons with Reduced Mobility modifications began in June 2018, with toilet retention tanks also being fitted. On 14 October 2018, these units transferred to Transport for Wales. In February 2019, the first unit was seen in Transport for Wales colours. These are set to be replaced by 2023 alongside the rest of the Transport for Wales fleet by a total of 77 Class 197 units.
British Rail Class 158