Speculation has been rife about how the thriller will wrap up in its final episode on Sunday, but Mercurio has refused to confirm whether the character of Home Secretary Julia Montague, played by Keeley Hawes, has really been killed off.
He told ITV’s This Morning: “We’re all sitting back and enjoying the speculation. It’s great that people have their own theories. Actually, I do look at some of the bigger theories and it’s interesting that occasionally there’s a grain of truth.”
Mercurio previously killed off a character played by Hawes in his series Line Of Duty, and he said: “The fact that it happened before makes people swing towards the idea that she must obviously be dead.
“But then there are other things that are in the drama that make the observant people swing towards the idea that possibly that’s a ruse.
“We’re just sitting back and enjoying the response and the speculation.”
Mercurio did confirm that only one ending has been filmed, saying: “There isn’t an alternative ending.
“We weren’t in a position where we could commit to doing that and shoot it different ways and then edit it different ways. We definitely have a conclusion.”
Mercurio added that conversations have begun with the BBC about a second series.
Meanwhile he also hinted at what’s to come in the upcoming new series of Line Of Duty, currently being filmed in Belfast. “We’re answering some of the questions that were left over from series four and we’re also starting a whole new investigation that will carry through the six episodes,” he said.