It’s back for a third series this week with Greenock-born Martin as uncompromising English cop DS Steve Arnott.
“The accent is a big thing for me as it needs to be good and not at all noticeable,” says Martin.
“I try to stay in it all day as my normal accent is strongly Scottish and going from that to Steve’s is a big jump, but it’s quite tiring.
“We’re so dialogue-heavy there’s no room for error but people forget that your mind is working when you’re constantly doing an accent.”
The hit BBC2 series focuses on the work of anti-corruption police unit AC-12, with Daniel Mays’ firearms officer under investigation after a suspicious shooting.
Most actors try to find their character’s better qualities but Martin says that’s really not the case with Line of Duty.
“Steve’s still the same guy – arrogant and annoying,” laughs Martin, who has a house in Los Angeles with fiancee Tianna Chanel Flynn.
“He’s a lot of fun to play as I try to make him as dislikeable as possible.
“Just because Steve’s got a moral centre and is good at his job, it doesn’t actually make him a likeable person.
“He thinks he’s better than most other people and he wears waistcoats!
“One of the reasons I wear them and make him talk like a bit of a smart alec is that I knew a guy back home who was like that.
“He also used to pull these beautiful girls even though no one else could see the redeeming features in him, which is Steve to a tee.”
Line of Duty BBC2, Thursday 9pm.
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