For six seasons, fans of BBC crime drama Line of Duty have enjoyed the turbulent twists, intriguing character development, unsolved mysteries and near-indecipherable acronyms associated with the series. Even repeated phrases, such as Ted Hastings' "Mother of God!" at every plot reveal, his insistence that his officers work to the "letter of the law" and Kate and Steve's inability to speak without calling each other "mate", have a subtle charm to them, in a way that one finds themselves eagerly awaiting each phrase like a sort of Line of Duty bingo card. In recent seasons, the emergence of the series' ultimate mystery had taken place, with the final corrupt police officer codenamed "H" still at large.

Speculation was rife amongst the fanbase, as countless fan theories hypothesized as to the true identity of "H", the fourth corrupt officer that Season Six had promised to reveal. However, as the final episode drew to a close, it was revealed that "H" or "The Fourth Man" was in fact Ian Buckells, a side character for most of the series who Anti-Corruption Unit 12 had already arrested for his involvement with organized crime earlier that season. Buckells' reveal came as a disappointment to fans, who expected a less low-key unfolding of the series' big mystery upon its final episode.

To some, Buckells seemed too obvious to be H, to others too small-scale. The character had been in the series since Season One, but in short snippets however, and was never seen in any dramatic high-tension scenes. Compared to the other three corrupt police officers caught by AC-12, Buckells seemed somewhat small-fry.

The sixth season was confirmed by series creator Jed Mercurio to be the last with a tweet in which he thanked the actors who portrayed the series' three main protagonists and the team behind the show. Vicky McClure, who played DI Kate Fleming, also tweeted a message which read "now...let's wrap this up" prior to Season Six's final episode, adding to the hype around the reveal of H's identity. However, the final words of the episode, in Line of Duty's traditional subtitled ending ,being "AC-12 have never been weaker "is an unusual way to conclude a series, and seemingly leaves the door open for a revival of the unit's fortunes in a future story.

Adding to this, earlier in Season Six Ian Buckells is seen in prison, being threatened while another character involved in organized crime, Jimmy Lakewell, is murdered before his eyes. The man doing the killing clearly says to Buckells "Now you watch what happens to a rat", indicating that Buckells could be hiding the true identity of H and taking the blame for his crimes. This theory would fit Buckells' character, who up to this point has not seemed capable of running an organized crime group from behind the scenes.

Many viewers had also hoped that H would be revealed to be DCS Patricia Carmichael, a high-ranking police officer who had almost seen Ted Hastings, the head of AC-12, falsely imprisoned before his name was cleared. Carmichael also stood to takeover AC-12 and merge the team with other anti-corruption units in the lead-up to the finale. As the events of the final episode took place, AC-12 uncovered Ian Buckells as H before the unit was dissolved by Carmichael with no repercussions for the character.

Another name that viewers believed to be involved in organized crime was Carmichael's boss Philip Osborne, another high-ranking police officer who had previously attempted to get series lead Steve Arnott to lie during his time in counter-terrorism. In Season Six, Osborne has been promoted to the very top of the Central Police Force and continues to maintain that there is no institutionalised corruption within the police service. It seems clear that Osborne is corrupt in some way, but the possibility of him being H was not explored, an opportunity missed perhaps.

The BBC have been forced to defend the Line of Duty following social media reaction to the finale. The corporation released a statement which read: "We always aim to produce the most captivating drama possible for viewers to enjoy and we're extremely proud of this series - for the recognition it received and for the support from viewers. The series 6 finale deliberately aimed to wrongfoot viewers' expectations. Out of an audience of 16 million, we recognize that the programme makers' dramatic choices won't have met with everyone's approval."

Line of Duty's creator Jed Mercurio, also released a statement on twitter, in which he used research in an attempt to show that not all viewers were disappointed with Season Six's final episode: "No-one disputes the Line of Duty finale divided social media opinion but the audience research so far shows a far less extreme picture. We knew a "down" ending would rate less favourably with some viewers, however, all seven episodes varied by under 10% on average viewer score. The research determines the episode ratings based on randomly polling viewers, rather than sites like IMDB where scores can be skewed by users strongly motivated to register their immediate anger/adulation. 1000 random viewers submitted scores from 1-10 which have been used to calculate the Appreciation Index (AI) as a score out of 100. The AI for the "down" finale was only 7 points below the next lowest in Season 6 (Ep 1)."

Despite Line of Dutycoming to a close, it appears that Mercurio and Vicky McClure (DI Kate Fleming) are working on something new. A six-part ITV thriller Trigger Point is coming to screens in 2022, and will focus on counter-terrorism policing and the Metropolitan Police's bomb disposal squad. McClure revealed details of the new series with a post on twitter.

McClure is set to play the role of Lana Washington, a police officer with a military background put under pressure to search for answers during a gruelling terrorism campaign. In a statement, the actress added: "I'm really looking forward to creating a strong, bright and troubled character in Lana Washington. Daniel Brierley has produced a brilliant and nail-biting script. I can't wait to get started later this year."

Mercurio, meanwhile, had this to add: "Everyone at HTM Television is honoured Vicky McClure will star in Trigger Point, Daniel Brierley's breathless thriller that will have viewers on the edge of their seats."

McClure's co-star Martin Compston (DI Steve Arnott) has also been busy since the conclusion of the series. Directly after finishing the drama, Compston will star in Vigil,a new six-part thriller from the team behind the Line of Duty.The series will air on BBC One, and will focus on the mysterious disappearance of a Scottish fishing trawler and a death on-board the submarine HMS Vigil.

The Scottish actor has also been filming a second season of BBC drama Traces, and mini-series The Rig.Tracesfollows a young lab assistant who discovers a link to her past in a fictitious case study, while The Rigfocusses on the crew of an oil rig who become cut-off from the mainland when a dense fog rolls in. The Rigalso features Compston's Line of Dutyco-star Mark Bonnar, who played Detective Chief Constable Mike Dryden in Season Two.

Lastly, Adrian Dunbar, who portrayed Ted Hastings in Line of Duty,is currently starring in BBC comedy series Inside No.9.The series focusses on a mix of stories, each taking place behind a different door marked "Number Nine". Inside No.9 is created by Steve Pemberton and Reece Shearsmith, and is in it's sixth season.

Dunbar is currently filming Emily, a movie about Wuthering Heights author Emily Bronte. The story is set to chronical the writer's early life before her untimely death at the age of 30. The film marks Frances O'Connor's directorial debut, who had this to say about the production: "Emily Bronte's work and words are full of passion, feeling, violence, and fierce intelligence. In creating an imagined life for Emily, she will live again for our audience. Her story is about a young woman daring to form herself, to embrace her true nature, despite the consequences. Emily is, in fact, a love letter to women today, especially young women, a calling to them to challenge themselves to connect with their authentic voice and potential. I am so excited to work with such a thrilling, talented, young cast; luminous, intelligent, and spirited." The movie will also star Sex Education's Emma Mackey, Dunkirk's Fionn Whitehead and The Invisible Man's Oliver Jackson-Cohen."