THE GUARDIAN – Richard Madden can recall with clarity the moment he crossed the line with Idris Elba. The “odd couple”, as Madden describes himself and his Bastille Day co-star, were just days into the action film’s three-month shoot in Paris. The 29-year-old actor plays a pickpocket who becomes the unlikely partner-in-crime of a former CIA agent (enter Elba, giving the Bond audition of his life). They had been rehearsing for a car chase, and were preparing for the first take, when Madden decided to wind Elba up. “I turned to him and I said: ‘Are you going to do it like that on the take?’” Suddenly there was tension in the air. “I could see him thinking: ‘What the fuck’s this guy doing?’ It was great. At the end of the scene, he realised what I was doing and was like: ’You’re a fucker! You’re just trying to fuck me up!’” Madden laughs, then lets out a long breath. “He could have taken it the wrong way…”

The opening passage of Bastille Day, in which Elba’s agent chases Madden’s petty thief across Paris, sets a pace that doesn’t let up. But though the film serves up plenty of moments for Elba to showcase his action-man talents, it’s also an effective two-hander. The dynamic between the duo develops into something reminiscent of the odd action couples of old (in Lethal Weapon or 48 Hrs). When, on the verge of big shootout, Madden’s character asks Elba: “Can I have a gun?”, and gets a withering glower in return, it feels like Joe Pesci pestering Mel Gibson. Madden says that he improvised the line, and you can tell he’s proud it made the final cut.

Winding up Stringer Bell may be a bold move, but would you expect anything less from the King In The North? Madden’s turn as the ill-fated Robb Stark in Game Of Thrones ended with him being offed in the show’s most famous set-piece. Since then, his biggest roles has been playing the lusty gamekeeper in Jed Mercurio’s TV adaptation of Lady Chatterley’s Lover and the more clean-cut prince in Kenneth Branagh’s Cinderella. But this year looks set to be bigger: as well as Bastille Day, he’s landed a key part in another big-budget TV drama, starring alongside Dustin Hoffman as Cosimo, the charismatic heir to the ruthless Medici clan in Medici: Masters Of Florence.

In person, Madden is more self-deprecating than self-assured. Our interview is littered with phrases such as “I’ll keep doing the things I don’t know if I’m good enough to do” or “It will probably slap me in the face at some point”. He confesses that, during the filming of Bastille Day (the release of which was postponed due to last November’s Paris attacks), he kept up his American accent even when off-set, not for reasons of method acting, but so that his colleagues could understand him. His Scottish accent is so broad, he says, that he often plays the American to get by “because even Siri doesn’t understand me! She doesn’t get a word I say. I’m like, ‘What time’s the next train?’ And Siri’s like: ‘Calling: ex-girlfriend.’” Fake accent he may have, but his face is still recognisable to ardent GoT fans. He gets stopped in the street a lot. I suggest he dress in disguise. “I’ve done that before,” Madden nods. “The problem is, you look like someone who is trying to be in disguise and it actually [looks] worse.” He describes the effect of this second-guessing over being recognised as “fucking with your head. You think: ‘I can’t order the fucking spaghetti because there’ll be a photo of me on the internet with tomato sauce down my face,’ and the next thing, no one’s recognised you at all.”