Martin Compston reveals new look for DS Arnott in Line of Duty series five

The Scottish star explained that it was for Line of Duty (which he was in the middle of filming) and not the period film – although, to be fair, his character in Mary Queen of Scots does sport an impressive beard too.

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“Everyone is giving me a bit of stick for this beard for Line of Duty," Compston laughed, "but the beard I have in Mary Queen of Scots – now that’s a beard!

"But with Arnott, people are quite intrigued by his beard because he’s normally quite clean cut.”

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Up until now the determined (some would say cocky) Line of Duty detective was notable for his waistcoats, a look some viewers suspected was copied by England football manager Gareth Southgate during the 2018 World Cup.

Does Compston think Southgate copied Arnott’s look?

“I think he might have, but maybe I copied it from Sherlock Holmes,” said Compston. “That was one of my ideas behind it; all the great detectives wear waistcoats, and you look like a bit of a dick if you wear one. I like that. He [Arnott] has got an arrogant side to him.”

Compston was full of praise for his new film Mary Queen of Scots starring Saiorse Ronan as Mary, with Margot Robbie playing her nemesis Elizabeth I.

The film charts their political and dynastic battles which ended when Elizabeth signed her cousin’s death warrant as Mary’s conspiracies against the English Queen come to light.

“It’s perfect for right now, so apt,” said Compston. “The men were bastards.”

The film also sees David Tennant appearing as the blood and thunder Protestant preacher John Knox who rails against Mary.

Compston praised his fellow Scottish actor: “It was brilliant seeing David’s transformation because David’s such a nice guy, and any account I have read of John Knox [suggests] he was a miserable bastard.

"He uses quite ugly language about women, very provocative. He splits opinions in Scotland. He can be a nasty piece of work and David looks like this dreary old man. Sometimes when you see these things and I walked on set I didn’t recognise him.”

Mary Queen of Scots will be released in UK cinemas on 18 January 2019. Line of Duty series five is expected to air on BBC1 in 2019.