Speaking at an Anatomy of a Hit event dedicated to the police corruption series, Mercurio revealed he has written the first couple of episodes of season five, which is due to air next year.

He said of the next series: “It feels like things we haven’t done before, characters we haven’t seen before and that’s part of the construction of the series; the architecture that allows us to rejuvenate the format.

“Possibly we kind of arrived at that accidentally but…we have this situation where the audience becomes intrigued about what we’ve got to offer based on who the guest lead is going to be, what character they are and what the fundamental premise is.”

Line of Duty has already been commissioned for two more series and the show has become renowned for its complex lead characters. When asked if season five or six will feature as fascinating a female lead as Lindsay Denton or Roz Huntley, Mercurio  said, ‘maybe’ but the new episodes will further explore the personal lives of AC-12’s main characters - Ted Hastings, Steve Arnott and Kate Fleming

Quizzed by presenter Anne Robinson and members of the audience about the future of the show beyond the next two series, showrunner Mercurio said a lot depends on “how season five  performs”.

He explained: ”If it does very well and the current regime remains as supportive as they are there will be opportunities to discuss season seven and I think if for whatever those situations don’t apply then I think almost certainly season six will be the last…But we’re really happy that it’s ongoing. I don’t think any of us at this point is looking to wrap it up.”

Programme makers World Productions creative director and Line of Duty executive producer Simon Heath said: “We’ve never been pressured to be on air every year, so we get a break from the show to go away and do other things and then come back to it…it feels quite fresh, every time you sit down to another series.”

Asked whether or not the series could spawn a film, actor Adrian Dunbar, who plays Hastings, joked,“Yes! Ted’s Excellent Adventure” but Mercurio said: ‘No, we’re a TV programme’.

Speaking about the genesis of the show which launched in 2012 on BBC Two, Heath paid tribute to former BBC drama boss Ben Stephenson for finding the money for the show at a time before Netflix made drama more fashionable.

Initially the show was turned down by BBC but Stephenson found the money for it to be made on BBC Two. Mercurio said, “BBC One did turn it down, it was originally offered to BBC One” but when asked by Robinson where that controller is now, he replied: “I don’t really want to say”. 

Alongside insights into the creation of and length of time it takes to film the drama’s infamous long, tense interview scenes (the longest take was 35 minutes) and how Mercurio creates the characters and devices that have thrilled over seven million viewers, Robinson asked Dunbar if he was worried it will be Hastings’ turn next “to be a bent copper””

Dunbar responded with a laugh: “Yes that is a worry!”