It was on the first day of filming 12 Years A Slave that all Chiwetel Ejiofor's plans fell apart. He was in Louisiana - and in character - picking cotton when the heat hit him hard. "It was a sudden realisation of what being out there was going to be like," he says. "It was about 108 degrees, high humidity. Everything up until that had been theory."

It was on the first day of filming 12 Years A Slave that all Chiwetel Ejiofor's plans fell apart. He was in Louisiana - and in character - picking cotton when the heat hit him hard. "It was a sudden realisation of what being out there was going to be like," he says. "It was about 108 degrees, high humidity. Everything up until that had been theory."

He'd been in New Orleans for a while, for research and violin lessons. "But if you're hopping in and out of air-conditioned cars or at the hotel and rehearsals in people's apartments you are aware that it's hot. But

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I hadn't really factored it in. I hadn't thought about it.

"I think I'd gone on set at maybe 7.30am, eight o'clock, something like that. And by 11.30, 11.45, it was getting up to 108F and I was pouring with sweat. I started to think: 'How is this possible?' All the stuff I had prepared was kind of out the window because it was 108 degrees and there was no shade."

As it turns out that day was not normal, not even in the southern states. But let's take that day and run with it, stretch it out into a metaphor for life. For your life, my life and Ejiofor's. A kind of contemporary take on the old saw, "life is what happens when you're making other plans".

That's certainly true of the man

Ejiofor was playing, Solomon Northup,

a musician, a free man, tricked into slavery in Washington DC in 1841, sold to two owners, the second of them alcoholic, abusive and frankly disturbed (played

by Michael Fassbender, who's scarily believable).

Steve McQueen's film 12 Years A Slave has arrived in British cinemas festooned with Oscar talk (for both the film and for Ejiofor's impressively composed performance; he already has a Bafta Best Actor nomination). Yet talking about the red carpet would seem slightly strange in the wake of seeing the film. It's a potent, poised piece of cinema that addresses a history in which we are all complicit to some degree.

And so when we meet in a hushed, expensive London hotel room a hop, skip and a jump from Oxford Street we end up talking about slavery and migration and family history and not about Oscar parties. It's an all too brief conversation so I don't even have time to ask him what designer label he'll be wearing to any putative awards ceremony.

If it comes to that he'll look fine no matter what, I imagine. He's a good-looking man. If I was to be reincarnated as a contemporary male actor I'd always trade up and go for Clooney. But having met him there would be worse choices than Ejiofor. He's tall, he "wears that suit" (as Jennifer Lopez says to Clooney in Out Of Sight) and speaks slowly, carefully and always intelligently. In the dim light of this hotel room the scars on his forehead - from a car accident that killed his father and left him in a coma aged 11 - are difficult to pick out.

Talking about the role and the film -

a film that will quite likely elevate his recognisability more than a little - the

word he returns to again and again is responsibility. He was clearly aware of the weight of telling this particular story.

"I had never seen a story from inside the slave experience, so I was very aware of what it might mean and what it would mean to me to fail. A risk that would be so appalling to take because I would feel so hurt by that and with myself."

Is that sense of failure something he feels every time he walks on to a set? He's walked on to a few, from Love Actually to American Gangster and Dirty Pretty Things, as well as stand-out performances on the small screen for Stephen Poliakoff in Dancing On The Edge and in Hugo Blick's compelling BBC thriller The Shadow Line. Or was it peculiar to McQueen's film?

"It was quite specific to this. I've never

felt that sort of self-doubt before, not a

self-doubt that was that destructive, that was a real voice in my head."

How close did you get to saying no? "It was a possibility. It was a definite possibility. I sort of put Steve on pause in a way and said, 'Listen, I need to have a think about this.'

"He was very surprised. I could sense he thought the conversation would be about how amazing this project is. There was a sense of excitement in his voice. He was taken aback a bit."

It took Ejiofor reading the book the screenplay was based on, Northup's autobiography, to persuade him that this was a role to grab. "When I first read the script I didn't necessarily see Solomon in it. I saw the story of a man and that man could be approached from a number of different angles. But when I read the book Solomon shines through. It's his biography so I suppose he would, but he shines in this extraordinary way. There's this gentility, this humility, this poetry. You realise this is the psychology of a man who could survive something like this with his mind intact. This is the kind of person who could go through this experience and then write about it without hatred.

"There are moments that are completely devastating, but done so simply and with a love of life and a love of people that you think that's really a guy to pursue and play."

The film deserves all the plaudits it's been getting. It manages to be both stark and nuanced, full of horror (the lynchings are hard to take) and a kind of discovered beauty. Yet one of the things that bothers me about the film, or at least the way it's being promoted, I tell the actor, is the way it's been spun in some quarters. There's a notion that it took these two Brits - Ejiofor and McQueen, along with Fassbender, an Irishman - to finally tell the story of American slavery. As if - and this is the thing that's bugging me, I say - that story was a uniquely American tale. As if it started and ended within the borders of the United States.

That boosterism is beyond his control, of course, but it does need saying this is as much a British story as an American

story, surely?

"Well, that's the truth," Ejiofor says. "It does worry me if people in Britain slightly deflect that and suggest it's a purely American concept when of course Britain ran not only a brutal slave trade in America when it was the 13 colonies, but a brutal slave trade in the West Indies. Any suggestion that it can be divorced from British history is completely crazy."

Well indeed. And that includes Scotland. Where do you think Steve McQueen's surname comes from, after all? And you can trace much of Glasgow's 19th-century urban splendour to riches garnered from tobacco and sugar, both of which were reliant on slavery. The fact is the story of slavery is a complex one that resonates down the years. But then, I guess, the actor knows all about that.

When, I ask Ejiofor, was he first aware of the concept of slavery? "Very early. I was born the year Roots came out so I think it was something that was always there. And there was a point when it became explicit, when I had a conversation with my parents. That's when the geography of slavery became apparent and that idea of what the African diaspora means. Because you're aware of the West Indies and you're aware of African-Americans, but you're not necessarily pulling all these things together when you're a kid. Then it's explained. 'These are from the West Indies, but they look more like you because … And that's why Michael Jackson - at some points in his life - looked more like you.'

"It's the first balloon to burst about the innocence of the world for a kid. Finding out about slavery is the first time you find out that the world is a much darker place than you assumed."

The shorthand version of Ejiofor's story goes like this: He was born in 1977 in London's East End, the son of Nigerian parents. He was educated at Dulwich College where he joined the drama department, which led to a place at the National Youth Theatre when he was 17, and then a scholarship to London Academy of Music and Dramatic Art. Aged 19, and only three months into his course, he was chosen by Steven Spielberg to play a small part in the slavery epic Amistad and that was his course set. An actor's life for him. One that now sees him divide his time between London and Los Angeles.

The longhand version - the version that places it within his family's larger story - is possibly more interesting and certainly at times much more harrowing.

Ejiofor's parents had moved to London in the seventies after a spell in Paris. They were both members of the Igbo community. It's worth noting that most slaves in Jamaica, the West Indies and Virginia after 1750 were Igbo. His father Arinze was a musician as well as a doctor, so performance was part of the family narrative. Father and son were in Nigeria when Arinze was killed in the car crash that also injured Ejiofor who spent 10 weeks in hospital.

His father's death is inevitably something the son's interviewers are drawn to, but I'm interested in his mother Obiajulu, a pharmacist. It's difficult to imagine what she went through; a young widow bringing up a young family. "She had three kids and was pregnant with my youngest sister so it was a complicated time for her. But the thing about my mother is she is an extremely resourceful person, which she demonstrated from when she was young."

Obiajulu and her parents (Arinze too for that matter) lived through the Biafran War in the sixties. Nigeria gained independence in 1960 and adopted the borders of the old British colony. A coup in the mid-sixties led to riots and massacres. In the north the Igbo community was soon being targeted. "The war created this extraordinary situation where my grandparents were very middle class. My grandfather was an accountant for the mining corporation in the north of Nigeria where the pogroms started against the Igbos. He was forced quickly to move back to the east. The family tried to rebuild their middle-class existence and that's when the war started in earnest."

The creation of a breakaway state by the Igbo led to civil war in 1967 and Ejiofor's grandparents and family were constantly on the move, to newer and meaner homes.

The cost of living like this soon became all too evident. Arthur, Obiajulu's brother, died. "He didn't die in fighting, but like so many children out of circumstances," Ejiofor says. "He had a massive asthma attack and died, which was a breaking moment for the family." It was wartime. Medicine was unavailable.

"My mother was about 14 and the oldest and it was her responsibility to try to hold the family together, which she took on her shoulders and managed to do. My grandfather got sick and my grandmother was distressed. And my mother was there.

"My grandfather passed a couple of years ago but I spoke to him before he died. He and my grandmother would constantly say that my mother helped them in the war. She was 14.

"So it contextualises it for me. And the older I get the more I'm aware of what she did for me and my brother and my sisters and how hard it was for her. But one realises she had spirit and a real, fiery love of family that nothing was going to destroy."

As he talks about his mother I think back to what he had said about Solomon Northup, that idea of discovering in his writing "the psychology of a man who could survive something like this". Change the gender and you surely have Obiajulu.

This is a story about family, about migration, about how history shapes us. This is Ejiofor's story. It could be anyone's.

"What have you inherited from your parents, Chiwetel?" I ask before I leave. "So many things, I hope. How many I actually got …" He smiles. "I got very fortunate with my parents. They have always had a real love of life and a real belief that nothing is impossible if done with striding out and seeing what your limitations are and perhaps pushing beyond them. I hope that's what's been passed down." n