I meet Idris Elba in London just hours ahead of the premiere of Mandela: Long Walk to Freedom, a big screen adaptation of Nelson Mandela’s autobiography in which Elba takes the title role.

Minutes before the gala screening begins news trickles through to an audience that includes the Duke and Duchess of Cambridge and Mr Mandela’s daughters, Zindzi and Zenani: Nelson Mandela is dead.

As it happens, when I playback the interview, there’s already a sense of requiem: Elba talks about the similarities between Mandela and his Sierra Leonean father, who died just a few months ago. He remembers seeing Mandela on the wall of his childhood home in east London.

“My dad was fascinated with African leaders,” says Elba. “There was a picture of Mandela in my house since long before he got out of jail.”

Unsurprisingly, the actor was keenly aware of the responsibilities required by such a role.

“It’s like: what?” he says. “You’re going to play God now. It’s not so easy to turn around and say: ‘Okay. I’m God now.’

At 41, Elba is strikingly masculine, slyly humorous and effortlessly cool. Today, bass notes carry his soft voice across the table in a crowded lounge. He prefers to do his interviews this way: “I don’t like sitting in hotel rooms for interviews. It drives me nuts. I need to have a real conversation.”

True to his word, he converses rather than answers: “You know grapes contain this compound called Resveratrol?” he says, as he offers a fruit basket. “They’ve turned it into an anti-ageing formula to rejuvenate your skin. But I’d rather just eat grapes.”

He smiles: “Cheaper than Botox”.

Mandela: Long Walk to Freedom truncates nine decades of Nelson Mandela’s personal history into a two-hour film. Idris Elba brings charisma and imposing physicality to a role that encompasses 50 years and seismic changes.

“The younger Mandela is a very different man to the one who left prison,” notes Elba. “That’s a fact. So I had some license for interpretation in those early scenes. But the ageing process was all about the details. You needed to get to a point when the audience would say: I recognise him now; that’s the Mandela we know.”

Nelson Mandela, he says, represents a “very big pair of shoes to fill.” But standing at 6’ 3”, Elba had to rethink his movements in order to approximate the older, frailer Mandela.

“Nobody knows better than me that I don’t really look like Mandela,” says Elba. “I was super- sensitive to the idea. And I really wanted to make an effort to convince an audience – all of whom are going to have at least some degree of familiarity. Everybody knows that hair and that voice.”

Though the film is reverential in tone, honest depictions of Mandela’s activities as a freedom fighter ensure that Mandela: Long Walk to Freedom is less hagiographic than previous screen incarnations of South Africa’s first black president.

“He’s a lawyer – a man of high society – who turns vigilante, who trained as a soldier, who went to Sierra Leone, my father’s homeland, to raise money for the cause. How brave is that? He was 37 when he became a radical. He was in jail by 43.

“So those six years are an interesting turnaround. We wanted to acknowledge them. We wanted to be as honest about him as we could be: honest about his marriage, his personal life, his achievements. It took him 27 years in jail to become the man we knew. It wouldn’t have meant anything if we started the film in jail.”

Idrissa Akuna Elbagrew up in East Ham with his Ghanaian mother and a Sierra Leonean father. He shortened his name to Idris while attending school in Canning Town, where weekly drama classes introduced him to his future profession.

“I was a shy guy. If there was a party, I’d be in the corner. I remember being about 18 or 19 and realising there was actually a living to be made out of acting. Up until that point it was one drama class a week at school where I had an amazing time. It’s only-child syndrome. We like making shit up.”

He left school wanting to be a DJ, but he eventually took a job alongside his father Winston at the Ford factory in Dagenham.

“My parents are working class immigrants. By the time I was 17, they had been here for 20 years and all they did was work. So they expected me to be the same. My dad said: ‘Come with me to work and we’ll get you some real money. A cheque. Actors wait around forever’.

“I did that. And I saved the money so I could step away and have time to audition. And I got into it quite easily you know. I got my first job as a stagehand easily. I got my first play easily. And just kept working from there.”

His parents need not have worried about his work ethic. A polymath, Elba works as a DJ under the moniker DJ Big Driis, appears on Jay-Z’s 2007 American Gangster soundtrack and has just recorded Mi Mandela with Remi Kabaka and Maverick Sabre, a musical chronicle of what Elba experienced as he played Mandela.

“I loved the music in South Africa so much that I promised to go back and do something about it,” says Elba. “And I did. We put together a house band and I brought down other musicians and I’m excited about it.”

There’s talk of an Oscar nomination for Elba’s Mandela, but if it doesn’t materialise one feels there’s bound to be another chance down the line. A mesmerising screen presence, he makes film acting look and sound effortless: “Essentially, it’s the same business everywhere. Show up. Say your lines. Take your marks.”

But he would say that. Elba’s career, to date, has been characterised by stealth. The actor was working steadily on both sides of the Atlantic for some 10 years – in indie US military satire Buffalo Soldiers, in French comedy Belle Maman, in BBC’s Silent Witness – when his depiction of drug kingpin and aspiring businessman Russell “Stringer” Bell in HBO’s The Wire propelled him into stardom proper and onto People magazine’s 100 Most Beautiful People in the World poll.

“I don’t remember people recognising me when I was doing Family Affairs on Channel 5,” he smiles. “The Wire was massively gradual. When I was making it I’d come home and no one knew a thing about it. And no one remembers me from Ultraviolet or Silent Witness – this is 2004. Then The Wire caught up and suddenly everyone was surprised: ‘Oh, he’s British’. But I didn’t feel the effect of it until I had left the show.”

Elba has gone on to establish himself as bona fide Hollywood movie star though a series of eye-catching turns in Takers, Prometheus, Pacific Rim and the Thor franchise.

“It’s an interesting time at the moment,” he nods. “I’ve been an actor for 22 years now. I feel seasoned. But I feel like I’ve suddenly got a lot more to do.”

Mandela: Long Walk to Freedom opens January 3rd