I don't know why some people are STILL so convinced that Joe Miller didn't kill Danny, and is covering for his son to this day grin I don't think there's ever been an indication that Joe's numerous confessions have been anything but genuine.
Only because it seemed like such a cop-out. The US remake of Broadchurch, whilst being a bit pants, did resolve the whole sorry mess a lot better. The big problem I had with the initial 'big reveal' is that they caught him because he turned on Danny's phone. Why would he do that? It made no sense - unless he turned on the phone to find out who it belonged to.
The majority of the conversation between Joe Miller and Mark Latimer occurred off-screen. We saw Mark asking Joe why he didn't tell the police what he'd just told Mark, but we didn't hear what he told Mark. It may have been a confession, it may have been something else.
Also, as I've said, I've read a few things from the production team that hint at a conclusion that would involve the murder of Danny. Apparently it was originally conceived as a trilogy, that may or may not suggest that the first series has some loose ends.
It may well be because I've seen far too many shows with big twists, where nothing is as it seems. I can't help being suspicious though.