For the benefit of the DIR, present in the room are telegraph.co.uk and a Line Of Duty fan. We’re about to commence interrogation under caution.

The cop corruption thriller’s fourth series, which has been clocking up record ratings, reaches its tense climax at 9pm Sunday on BBC One.

Full of procedural accuracy, forensic detail and shock twists, it’s a show that rewards close viewing. So have you been an observant witness throughout the drama’s four superb series?

Take our quiz to find out…