The actor, who has played Steve Arnott in the show since it began in 2012, posted a statement on Twitter after the “madness started dying down” following the episode’s broadcast on Sunday (2 May).
An overnight audience of 12.8m tuned in to watch the conclusion to the long-running “H” storyline, a reveal that left many fans feeling short-changed.
Many viewers also believed they were watching the show’s final ever episode and expected it to be more dramatic, especially after a series filled with car chases, shoot-outs and explosions.
Watch: Martin Compston shares Line of Duty pranks with co-star Vicky McClure
Instead, it was one of the show’s most sedate finales to dates when compared with previous outings, including the AC-12 showdown in which Gill Biggeloe (Polly Walker) enacted a deadly escape plan after being revealed to be a member of “H”.
Addressing this, Compston wrote: “Fully understand it wasn’t the ‘urgent exit’ type ending some anticipated but we appreciate you sticking with us”.
He also said he was “proud” of the episode and that he’s feeling a mixture of emotions in the wake of its broadcast.
“Felt many emotions from excitement and anxiety at the hype to relief that it's over,” he wrote, adding: “Now I just feel immense pride our show that started on Wednesdays on BBC2 has just smashed every overnight drama record since they began."
Mercurio retweeted Compston and also shared his own statement, revealing he “knew it wouldn’t be for everyone”.
There is no official word on whether the show will return for a seventh series, but the BBC has hinted it is happy to continue broadcasting the show should Mercurio wish to write more.
Meanwhile, Nigel Boyle – who played Buckells – defended the show from “disappointed” viewers while appearing on BBC Breakfast, stating: “You can’t have every series end with a big shoot out.”
While some were left underwhelmed by the reveal, clues hinting at the Buckells reveal in the show date back to as early as the very first series.
All six series of Line of Duty are available to stream on BBC iPlayer.
Watch: Vicky McClure and Martin Compston to get AC-12 tattoos after Line of Duty finale