Talking about the scenes in the interview room, Anna added: “You go demented.
“You are in a glass box with lots of people and actors, you know, we’re always mucking around and giggling.
“So it’s not difficult. It’s actually a really exciting thing to do.”
However, Anna did say that she had signed a “million forms” and so was not allowed to reveal any spoilers.
Line Of Duty continues on Sunday on BBC One at 9pm.