Line Of Duty star Martin Compston has urged fans of the hit BBC cop drama to "expect the unpredictable" when it returns later this year for a fifth season.

The Scottish actor stars as English detective Steve Arnott in the hit series, opposite Vicky McLure and Adrian Dunbar as members of AC-12, the internal anti-corruption wing that investigates members of the police force.

The role requires him to adopt an English accent and fans of the show have expressed surprise on learning he is not English.

He told the Press Association: "It's always a compliment if people think that, it means I did the other accent quite well, but it's a funny thing with accents because they can be like a costume to you.

"Because when you do an accent you do the voice and you immediately hear the character because it's separate from you, but at the end of the day it's a lot easier when you can go in and talk in your own accent or a clipped version of your own accent."

Previewing the fifth season of the show, which will feature Boardwalk Empire star Stephen Graham, he said: "Expect the unpredictable, as ever. That is pretty much it. It will be a big ride this year, it will be good."

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Compston can also be seen in current cinema release Mary Queen Of Scots, alongside Saoirse Ronan as the doomed Scottish queen and Margot Robbie as Elizabeth I.

Commenting on the film he said: "Everything I've ever seen or read, it's usually Elizabeth's point of view with Mary being a side note, but growing up in Scotland our history was always Mary with Elizabeth the big betrayer.

"I knew a fair bit growing up and all the characters and when a script comes along you hope something will do it justice and I really think it does."