GWR is running Pacer Class 143 units paired up with Class 150s on Exmouth to Paignton trains so that they comply with new disability access rules.
The Disability Discrimination Act 2005 says that all trains must be accessible by January 1, 2020. The latest standards include features such as: audio-visual information systems, easy to use handholds and handrails and an accessible toilet, if toilets are fitted. The Pacers do not have these adaptions and other regions have been given special dispensation to continue using them.
Pacers were due to be withdrawn from GWR trains by now but delays in cascading units from the London area to Bristol means they'll carry on operating for a few months yet.