The actor, 64, best known for his role as Chief Superintendent Ted Hastings, added fuel to speculation the BBC drama could be returning to the small screen.
The Greenock-born actor, best known for his role as cockney detective Steve Arnott in BBC series Line Of Duty, was filming scenes for forthcoming show Mayflies in rural Ayrshire.
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During the last season of the show, it had been suspected that Hastings - the head of AC-12 - could be the H - the fourth man at large during an ongoing hunt for the bent copper .
However, a new wild theory involves John Corbett s widow Steph, after viewers noticed an intricate clue hidden in her kitchen tiles during Sunday s episode of the show.
During the latest instalment of the hit police drama, many viewers took to Twitter to share their thoughts after noticing the very telling detail.
Ha! Line Of Duty viewer s latest H theory involves John Corbett s widow Steph, after they noticed an intricate clue hidden in her kitchen tiles during Sunday s episode of the show