Ivo, for Matt's, I used the 3 TOCs clue and guessed it would probably be South Central, South Western and Great Western services, so in the Pompey/Soton area, I just didn't know which stations all three actually called at as well as passing through.
As for yours/Neils, there is no third rail which must make the Southern unit a DEMU. It, however, has a headboard meaning it could easily be a red herring. The DMU's number has a P prefix, which I believe makes it a Laira unit. It looks like a fairly substantial station. I think Matt's answer of Exeter SD is very likely, but in order to be different I will go for Newton Abbot pre-rationalisation.