Both look to be ex-Alphaline Wessex Trains.
Below is what I can find from a search on Flickr:
This pic (not mine) of
158870 shows it at Cardiff in 2004 with Alphaline:
https://flic.kr/p/VBmsVR
This pic (not mine) shows it in 2010 at Haymarket wearing the Alphaline livery with ScotRail logo on it:
https://flic.kr/p/851oLy
This pic (not mine) shows
158871 at Newport whilst working with Alphaline Wessex:
https://flic.kr/p/oKQszJ
Interestingly, it looks like
871's been with Northern before. This pic (again, not mine) shows it at Huddersfield in 2008 with a small Northern logo under the first window behind the door:
https://flic.kr/p/N2bUu8