On a hot London hotel terrace overlooking the Thames waiters fuss about, while on the South Bank, swarms of tourists stop for selfies. Enter a cool-looking Aidan Turner, wearing jeans, T-shirt and black leather jacket. His dark hair is pulled back into a man bun and his face, which has launched a thousand tweets, is bearded. He’s shorter than you might imagine, but he’s got swagger.

On Sunday, Turner is back on BBC television as captain Ross Poldark, the conflicted Cornish hero of the Winston Graham novels. Expectations for Poldark’s return are high. It was one of the BBC’s biggest hits in recent years, and a third series has already been commissioned. “It’s quite rare, and ballsy too. I don’t feel any pressure but it would be a bit embarrassing if it bombed,” he says gleefully.

Turner swears he doesn’t pay attention to the ratings. As an actor, he says, you just “do what you do and hope for the best”. He says he ignores social media too, although he’s aware his hair has it’s own Twitter account and that his shirtless scything scene caused a Twitter explosion. “I don’t personally follow it and I’m not that interested, to be honest.” Following the buzz on social media would, he says, be “a tremendous waste of time”.

When Poldark came out, gritty crime thrillers were all the rage. He worried it might seem “dated or overly romantic or cheesy. I just didn’t know if people would be into it.” They were, and soon he was offered a role in the Agatha Christie adaptation And Then There Were None without having to audition.

Turner was born in Dublin in 1983 and went to school at St Mac Dara’s in Templeogue before leaving to join his older brother at Firhouse College in Tallaght, but he had little interest in getting good grades.

“I probably wasn’t a great student. I had a car when I was 17, so I used to just run out of school when I could, jump in the car and go play pool in Tallaght. I don’t know how I knew, but I convinced myself that my Leaving Cert results were never going to matter to me. I was shit at maths, no clue about Irish. English I did okay at . . . but everything else was close to fail rate.”

Once he was accepted by the the Gaiety School of Acting, school increasingly seemed like “a joke”. Two months after he graduated from the Gaiety in 2004, he got his first job with the Abbey Theatre and was never again stuck for stage work.

The jobs weren’t always brilliant. “Some were good, some were shit, but I learned a lot.” He emphasises the importance of failing, too, but it seems he never had much of the hard-up actors’ struggle. “I was lucky. I could pay rent. I was never sleeping on anyone’s couch.”

After a few stints on Irish TV, including a TV advertisement promoting eggs and a part in The Clinic, he made a leap of faith and moved to London. He rented a flat with the actor Charlene McKenna, from Co Monaghan. They were putting the keys in the door of their new place when his phone rang. She told him not to take it. “I said ‘No way – it could be my agent’, and it was.”

Two weeks later he was shooting the first of many nonhuman roles in Bristol – a vampire with a conscience in Being Human. Peter Jackson saw the show and noticed Turner’s elfin features. “He wanted me initially for an elf role and I don’t know what happened or how I ended up playing a dwarf for three years in Middle Earth.”

Pilot season panic

Six months after his duties on The Hobbit ended, Turner was in “Poldark land”. “ Poldark could easily have bombed. People might not have tuned in or liked what we were at, and suddenly I’m at the helm of this show that’s sinking quite fast and suddenly no one wants to touch you – certainly not the BBC or ITV – and then you have to start cracking into pilot season again.”

He has escaped the pilot-season panic so far, but he does spend time in LA. “I like it,” he says. “There’s a community of Irish and British actors; otherwise I’d be desperately unhappy.”

Turner laughs a lot and swears a little. He’s boisterous, boyish and a bit of a laugh. Sometimes when he’s serious, he leans in and narrows his eyes. What’s most striking about him is his confidence.

For years in Dublin, he says, he walked around with “unjustified confidence”.

“I was the one who’d walk out of the audition room and think, yeah, nailed it. I’d be on cloud nine, thinking I did such a great job.”

There were also horrible auditions, however. He did one for a JM Synge play “in the worst Kerry accent”. He walked out defeated, never wanting to audition for theatre again. And then he adds, without laughing: “I thought: ‘I need to take advantage of these looks before they totally fade.’ ”

There is more to Turner than a pretty face. He is a talented actor, and seductive on screen. He’s glad Poldark has meaty female parts and sincerely says he finds underwritten, pop-up parts for women “mortifying” to watch and to perform around. He’s a huge MMA and UFC fan, although he has never met Conor McGregor and imagines they wouldn’t have much to say to each other.

He has a studio in Dublin where he paints. His work is abstract and big and, in his own words, “shite”.

As a teenager he liked football and watching Woody Allen movies. He was a big fan of Superman, Columbo (he still loves Columbo) and costume dramas. He goes to the gym four to five times a week, but hates it. He does it because Poldark has a ripped reputation to live up to, and because he has to fit into his costumes. He’s a contentious actor who doesn’t drink when he’s working and only smokes when he’s drinking. He seems down-to-earth and happy. “I’m in a good place,” he says.

Last year Turner was burned-out after taking on too many jobs during a break from filming with the BBC. “I thought that was a great idea . . . but by the time Poldark started I was finished. I almost couldn’t work any more. I was dropping lines – and suffering – so this year I wanted it to be different.”

He’s straight up about being protective about his personal life and family. He mentions an interview in a British paper that got his parents’ details wrong (they are incorrect on his Wikipedia page too).

“That’s what I signed up for,” he says of fame and its trappings. But dragging his family into the equation bothers him.

No one in Turner’s family is even slightly interested in acting, so it’s curious that at a young age he became so convinced it was for him. “I don’t know where it started,” he says. “I was in Temple Bar and I walked past this acting place [the Gaiety School of Acting] and I thought, Imagine being an actor – I wonder what’s involved.”

He went in and signed up for an acting- for-camera class. He watched the older students and was in awe of their conviction. “They weren’t nervous. They were getting up and talking into the camera with this confidence, and I thought, I want some of that . . . I was a shy kid when I was younger but when I started that course in the Gaiety those walls broke down very quickly.”

Turner is committed to Poldark until March and says it’s too early to think about doing anything else, but his name keeps coming up when the role of a certain British spy is mentioned. Are we going to have a second Irish man play 007? “Cannot say a word,” he says straight, and then in a devilishly good Bond voice: “If I told you I’d have to kill you.”

Poldark returns to BBC1 at 9pm on Sunday