I have a pretty vivid memory of the movie I'm trying to remember so excuse the scarce amount of information i'm providing but I'll state everything I remember. This has been bugging me for months and I've still not been able to find out what it is and I believe it was out around the mid to late 2000's.
This is a movie based in either Afghanistan or Iraq (I remember it being a middle eastern country and set in modern ish time). It's about a group of different British soldiers (can't remember what branch) who start to commit war crimes and film and take pictures of it and they start to get worse and worse. If I remember correctly it escalates to a point where they are forcing a capture enemy soldier to open his mouth while they urinate on him and beat him.
I remember one of the characters who I believe is "Marc Warren" being an unlikable character who bullies a younger member of their team (who later commits suicide in a bath for feeling guilty about what he was pressured into doing).
After they come back to the UK they get found out because one of the people involved in the crimes shows the pictures and videos to his girlfriend and laughs and jokes about it while she's disgusted.
I also remember another scene where the guy who showed the pictures gets brutally beaten up by the people involved in the crimes. (I remember the possible Marc Warren character being in this scene). Then the rest of the movie is the legal process after word gets out of what they had done.
Apologies for not giving a whole lot of information but this is all I can remember about this movie and I'd like to see it again.