All 4 language series were shot on the same set in Madrid,
Each episode is a stand-alone psychological drama, consisting of the interrogation of an individual by a team of police investigators. Every scene is confined to just three areas in a single location; a police interrogation room, a darkened viewing room that looks into the interrogation room through a one-way mirror, and the hallway and stairwell outside the rooms.
Dialogue is the story.
I watched 7 episodes of the U.K. series.
Click PLAY or watch it on YouTube.