Line of Duty creator Jed Mercurio on why it was so "important" for character to be H and potential series 7

After weeks of clues and multiple red herrings, the "Fourth Man" was revealed to be DSU Ian Buckells (played by Nigel Boyle).

Following the finale, Jed Mercurio revealed why it was so important for Buckells to be the very man, who had eluded AC-12 for so long.

"I suppose it was really down to the decision to kind of hold him to account mid season. There were suspicions around him in the first few episodes, AC-12 get him in and they charge him, off he goes to prison and it feels like he's done and dusted," he told Craig Parkinson during an episode of Obsessed With... Line of Duty on BBC Sounds.

"And I think that if we kept him as part of the action all the way through, then it would have been very hard to misdirect the audience, so we were trying to present other candidates to take the kind of focus away from him, but it was always really important to me that it was someone who'd been in season one - someone who'd been there the whole time."

Jed says he contemplated making H one of the characters who came later on in the series, such as Marcus Thurwell (played by James Nesbitt) and Patrick Fairbank (played by George Costigan).

Chief Constable Mike Dryden (Mark Bonnar), who also joined the crime drama from series two, was also an option. However, he felt Dryden in particular wouldn't be "satisfying" enough for viewers.

He continued: "You know we did introduce some characters late. Thurwell came in late, we went back to Fairbank who appeared in season three, we had the Chief Constable, who had obviously been there since season one, but then I don't think he would have been a satisfying candidate because he'd been absent for so long. It would feel like we just brought him back in to pin it on him.

"Also because I think that we'd been directing the audience towards a particular image of the kind of character that he would be - that H would be a criminal mastermind. And we also wanted to maybe make a different commentary on the way in which someone can do a lot of harm, without necessarily being a mastermind."

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Jed says he purposely misdirected viewers on who H was by bringing old characters back, saying: "Part of it was the process of going through the season six design, bringing Thurwell back, because he was always a loose end when he was mentioned in season three. We actually had a lot more dialogue about Thurwell in the interview that was then cut, so we got much more of a sense of who he was, rather like Jackie Lafferty's murder. It was something that was always there to return to when we needed it. And it wasn't until season six that it was the right time."

He added: "And Carmichael was obviously really important as well. But again, you know she's come in season five, and she fits the bill in certain ways, but in other ways, she doesn't."

Nevertheless, Jed wanted to pay homage to the show's roots, insisting H had to be a character from series one due to the show's "heritage."

He said: "It was really about the heritage of the series, going all the way back to season one, where Dot Cotton says, 'Oh, can I just have a quick word' with Tommy Hunter in the back of the van."

Ever since series six aired on BBC One, we've all been dying to know whether there'll be a seventh series. With the finale proving to be a ratings smash as 12.8 million viewers tuned in to Line of Duty, you'd think the show's future would be set in stone.

Asked whether he'd started working on new material for another series, Mercurio laughed: "Well, we'll see about that."

He continued: "I just want to say thanks to the fans. It's so thrilling and flattering and humbling and rewarding people watch the show and talk about the show, and we wouldn't be where we are without the fans and I know that everybody involved in Line of Duty feels the same way."

Line of Duty Series 1-6 is available on BBC iPlayer now, and we have all the latest news on Line of Duty season 7. Check out the rest of our Drama coverage, or take a look at our TV Guide to find out what else is on.