Nadine Gordimer is 87 this year and as resistant to autobiography as ever. The Nobel prize winner, small, chic, straight-backed as a dancer, says "my private life is my private life" – a practical as well as a moral concern: what she calls the "jealous hoarding of private experience for transmutation into fiction".

It makes reading her non-fiction, collected earlier this year in a single volume and plain to the point of snappish, an exercise in sifting for lapses: the "bun-faced" nuns who taught her at school; her early "talent for showing off". The only thing that could deflect her from work, she once wrote, was "being in love", whereupon everything else flew out the window. She smiles indulgently. "Yes, I used to make bargains. I used to say I don't care if that book's published or not, it's the man that I want."

It is, for Gordimer, a year of collections; on the heels of the non-fiction, an equally large volume of collected stories, both covering a period from the early 1950s, when she started writing, to the present. It is a huge amount of work – "you're surprised that you've worked so hard" – and not even the main event. "That's nothing," she says, of the essays. "That was just on the side. Fiction is what really matters." Her writings about politics served a purpose, surely?

"They served a purpose only in that things happened – because you are not only a writer, you're a human being, with responsibilities. And so I would never write non-fiction if these things didn't occur. Even that very first essay in 1951, I wrote in the New Yorker because I badly needed the money."

Gordimer was in Britain from her home in South Africa this summer to deliver a lecture on the need for better library funding and the shortcomings of electronic books, which, in her arid style, she dispatches as pointlessly complicating technology. ("Kindle I assume has to be energised . . . the battery runs out. You can read a book anywhere, any time.") Her main preoccupation, however, is the state of her country, how far it has come and still has to go.

In that early New Yorker essay, Gordimer wrote of growing up in the "smug suet of white provincialism" in a small mining town outside Johannesburg. Her father, an immigrant from Latvia, was a watch mender; her mother was of English parentage – long after leaving east London, her maternal grandparents still subscribed to the News of the World by mailship. For liberal, white South Africans of her generation, there were, says Gordimer, two births; the literal one, and the moment of realisation that something in the culture around them was wrong. When she was very young she wanted to be either an actress or a dancer; she would mimic people ruthlessly and wonder, when they laughed, why it failed to occur to them that they would later, themselves, be targets. "Or perhaps it did, I do them an injustice and they didn't mind."

Writing as an aspiration came later. She traces it in part to an incident in the family home. Gordimer was 12 when their maid, Netty, who had been with them all her life, was subject to a random police search. "They pulled her mattress off, pulled all her clothes out, everything was in the yard, all her ordinary little possessions. It was a liquor raid – black South Africans could not buy liquor. My mother, father and I stood there and watched all this." The police found nothing and left. But it was her parents' failure to protest that shocked her.

"Now, I was old enough then to realise, from my reading, that you have to have a permit! But the police just came through the gate and did this. And neither my mother nor my father said to them, what are you doing here? One of the first stories that I wrote came out of that."

It was reading and writing that saved her, says Gordimer – "Kafka rather than Marx". She was given the best gift parents can give a young writer, she says: she was left alone. Writing from then on became "the scene of my greatest activity and my only discipline". Her favourite female character from fiction was Dorothea, "that priggish lioness from Middlemarch; her favourite motto from Camus: 'courage in one's life and talent in one's work.'" In 1963 she wrote, "the 'problems' of my country did not set me writing; on the contrary, it was learning to write that sent me falling, falling through the surface of the South African way life."

It put her at odds with her family, from whom she strained to get away as soon as she could, first to university in Johannesburg and then, in 1949, into an early marriage, with Gerald Gavron, a dentist. Looking back she sees things that, in her haste to leave, were lost. "Somehow the whole emphasis was on my mother. She was the dominant character. It's only now that I regret that I didn't ask my father about his background in Latvia – where he was born etc. He was from the usual very poor background and grew up under Tsarist tyrants when Jews couldn't go even to high school. But somehow, his past never became part of our conversation."

The marriage lasted a few years, and she found herself in her mid-20s, divorced and bringing up a daughter alone. It didn't feel precarious at the time, she says, but "I can't believe it, looking back! That I had this small child, no car, no medical insurance. I had a little sum from my divorced husband's father, who was struggling too, so I could feed her. And it didn't worry me for a minute. All my friends were in the same boat." She laughs. "And somehow we all had rather a good time together."

While working on her first novel, The Lying Days, Gordimer had started to write short stories, and in 1951 had one accepted by the New Yorker. Slowly, she began to write longer and more complicated narratives, although "I never thought of it as getting better, of saying to myself, I am getting stronger. I just moved toward it as if I were feeling my way down a passageway. It came absolutely naturally to me, the same way that you don't feel that you are growing, as a child."

Of all the misconceptions about her work, the one that riles Gordimer the most is that, while writing under apartheid, she felt obliged to use her fiction for liberal agitprop. She gets very annoyed at public readings when unsuspecting audience members ask if she hesitated to give black characters in her novels anything but virtuous qualities – snaps at them as if correcting an obstinately clung to stupidity.

"Look," she says now, "the process of writing fiction is totally unconscious. It comes from what you are learning, as you live, from within. For me, all writing is a process of discovery. We are looking for the meaning of life. No matter where you are, there are conflicts and dramas everywhere. It is the process of what it means to be a human being; how you react and are reacted upon, these inward and outer pressures. If you are writing with a direct cause in mind, you are writing propaganda. It's fatal for a fiction writer."

But in a repressive regime, isn't there a greater pressure on the writer, a sense of the stakes being higher?

"No. Then I would write non-fiction. I would divide my work and what there is that is worthwhile at all, in my view, of life, is the fiction. When I am doing something with a purpose, with a direct public purpose, then it's in the non-fiction."

Her early novels were often described by critics as "sensitive", something that continues to annoy her. "Sensitive to what? Sensitive to people's feelings?" Gordimer smiles. "No; I was not sensitive to people's feelings."

Work, for Gordimer, almost always came first. She had another child with her second husband, Reinhold Cassirer, an art dealer and refugee from Nazi Germany who ran Sotheby's in South Africa and to whom she would be married for over 40 years. Gordimer identifies the best moment of her life not as being awarded the Nobel prize in 1990, but as being at a party when, looking across the room, a woman said to her, "who's that divine man?" and she was able to reply, "my husband". He died in 2001. I notice that in print she always refers to Cassirer rather formally, by both names. "Yes. Just to show, indeed, that neither of us was an appendage of the other."

His priorities were the same as hers. "I'm afraid the children went to boarding school. My husband would never say, why should they go? He always put my work first."

In the 1970s, Gordimer's work brought her increasingly into conflict with the South African government, which banned several of her novels, including Burger's Daughter, probably her best, and then nervously unbanned it after an international outcry. It is a novel which looks unsentimentally at those activist families to whom everything was sacrificed for the cause; "their love life, their children, their parents; everything had to come second. It's the biggest sacrifice that anybody could make; but it was made by many."

She says, "it is the ultimate in humanity. That's what fascinated me with writing Burger's Daughter. You are born to such a family of the faith and then you are brought up within that faith, just as you'd be brought up in any religion."

Gordimer is an atheist, although once wrote of considering herself to have a "religious temperament". She dismisses this now as a moment of weakness – "if I said it at all. I probably did say it. I cannot remember." The point is, "how can anyone believe in these comforting fairytales, that there's somebody up there, whether it's Muhammad or Jehovah? Beautiful fairytales. Or punishing fairytales. This is an unpopular view."

She believes in the progress of the country she lives in, which has not, she says, been given sufficient leeway, particularly by liberals abroad, who can be smug without their liberalism having ever really been tested. Indicating Britain, she once wrote that if you live "in a country where people of a colour different from your own are neither in the majority nor the ruling class, you may avoid altogether certain complications that might otherwise arise in the formation of your sense of human values."

She says, now, of South Africa: "We are still in the morning after. I cannot emphasis strongly enough, we have had 16 years [since democratic elections]. That's all. Sixteen years. It's not even a generation. And here you, in Britain and America, have had hundreds of years of working towards democracy, and it's still not perfect; you've still got poor people, you've still got xenophobia. But we're expected to have done it in 16 years." One of the most successful elements of the post-apartheid era, she says, is "the impetus that's been given to the really practical side of feminism. Black women were subordinate not only to the apartheid law, but to the traditional law that your father, your brothers, your uncles could order you about and tell you what to do. So they were doubly oppressed. Now younger black women are extremely active, to the surprise and amazement and dismay of men their own age. But they're really becoming very strong."

She was a fan of Thabo Mbeki, although, she says drily, "he had the misfortune to be an intellectual" and had "the enormous fault" of being in denial about the Aids crisis. When Gordimer met Robert Mugabe, not long after he came to power, she thought "he really seemed to be a good man. It's the old thing of absolute power corrupts. He seems to have gone a little mad. And I also blame the wives. Very often the wives of these people become the world's biggest shoppers; including his. His first wife was a good influence, but this one comes to one of the biggest hotels in Johannesburg, brings her entourage, she shops like mad. She's also been to Dubai to shop. While all these people are starving."

What does she think will happen when Mandela dies? "I can only compare it to the 27 years he was in prison; stone walls do not a prison make. Mandela was with us when he was in prison. And in a strange way, Mandela will be with us when he's dead and gone. I don't know how long that will last. But he will become more of an icon, just as Mahatma Gandhi did."

She still writes in the morning for four hours, at a desk adorned with a postcard of Proust as a boy, a carving from the Central African Republic and a picture of the late anti-apartheid campaigner, Trevor Huddleston – "a lovely old photograph of him around a brazier in Sophiatown". On the subject of her own aging, says Gordimer, "well, first of all you think it's never going to happen. And I happen to have been married to someone who was 16 years older than I was, so the process of aging – my sorrow in that is attached to him. And my own? You are born, you grow, and then there's a stage in your life when you begin to die."

It is, typically, a bracing statement, not without feeling. The fiction might be what matters, says Gordimer, but it is the deeds of her life by which she wants to be judged. "That through the way you lived your life as a human being, rather than what you did as a writer, you could earn your way to being an African. I am an African. I am white. I in my humble way, and others in their much more brave way, have earned that right. Nothing else."