At a glance, Engagement, Gun-Britt Sundström’s classic novel of the 1970s, looks like a conventional story of young student love floundering in the face of ambivalence. The 79-year-old author, who is speaking via video call while cat-sitting for her son at his house outside Stockholm, has been taken aback by the novel’s return to favour. For a long time, Sundström tried to distance herself from Engagement, as writers will of their most famous book. But readers wouldn’t let her forget, and now, with publication of the first English translation, the million-plus-selling novelist and translator is enjoying a resurgence. Recently, says Sundström, “a young woman – in her 50s, which is young to me nowadays! – told me she had been given the book as a present from her father at 16 and it had changed her life. It had made her feel seen.” Sundström shrugs as if to say: this is nuts, but what can you do?

Engagement is not, after all, a traditional love story, but a study of a young woman’s fierce resistance to what she feels is the oppressive effect of being loved by a man. Martina and Gustav meet at college. Gustav wants their relationship to progress along traditional lines, an ambition that, Martina feels, risks leading her like a sleepwalker into a tedious, conventional life. At the casual level the pair’s relationship is loving and stable, but, observes Martina caustically, “Gustav is building so many structures on top of it that it’s shaking underneath them”. She wants to be loved but she also wants to be alone. She wants Gustav to stop repeating himself. When he asks her what’s wrong, she muses, “you can’t answer something like that. You can’t tell someone who wants to be with you always that he should be reasonable and ration himself out a little – if I saw you half as often, I would like you four times as much – no, you can’t say that.”

The novel is often described as a “feminist classic”, which Sundström resists – the implication being that any political objective undermines its integrity as a novel. “Feminist books ordinarily end with a happy divorce. And this doesn’t.” Instead, Engagement is a dense, thoughtful book that takes on questions of sex, boredom, self-esteem and what Sundström calls, “the moral issue; the question of can you treat another person this way, the way Martina [treats Gustav]? At the end, she herself comes to the conclusion that you can’t, it isn’t right. She can’t go on exploiting him, because he’s helplessly in love with her.” The book is less about the experience of loving someone than about being the object of love, and given current discussions around young women “decentring men” and “heteropessimism”, it is a startlingly modern novel.

It is also a dark comedy, something Sundström says tends to be overlooked. “It is a funny book! I often regretted that reviewers failed to mention that aspect.” How could it not be? Sundström herself is full of merriment. She turns 80 this summer and says, “I can’t believe it myself. Most of my friends are more or less the same age, and none of us can believe it. We are the young ones, aren’t we?” With her pageboy hairstyle and unlined face, she could be comfortably 20 years younger. (“Genes,” she says, flatly.) At the beginning of our conversation, Sundström mentions she is going through old diaries wondering what to keep and what to burn. “I’m cleaning up with the perspective of soon dying,” she says, matter of factly, and although the gentle art of Swedish death cleaning is a well-known phenomenon, it strikes me that even for a Swede, Sundström is thrillingly, inspiringly brisk.

Like her protagonist, she is also immune from groupthink to the point of awkwardness. In the novel, Martina wonders: “How can it be that most people lack self-confidence? And how can it be that I have enough self-confidence for an entire army? Of course I am beautiful and intelligent, at least intelligent enough to consider myself pretty enough – but that doesn’t usually help, does it?” It is still mildly confronting to read a young woman calmly assessing herself in this way, and Martina’s confidence is Sundström’s, the development of which goes all the way back to two key influences in her childhood. She was a great reader and identified most with swashbuckling heroes – the Scarlet Pimpernel and the Three Musketeers. And, along with her family, she attended a progressive Swedish church. “I grew up imagining that, to God, we are all equal and that my relationship to God, if I had one, was just as important as any man’s.”

Sundström’s political development as a feminist, meanwhile, was influenced by the cautionary tale of her mother’s life. Sundström’s father was a journalist, while her mother gave up work to raise Sundström and her sister in what, looking back, the novelist calls “a kind of tragedy”. Although she was never bitter, Sundström recognises that she was, “in a way, disappointed”.

The hardship of her mother’s generation makes Sundström sceptical of some aspects of the modern feminist movement, which she thinks has failed to acknowledge just how much has been gained. “We’ve had a backlash. Unfortunately, we were freer in my generation than in my children’s. My daughter told me she’s envious of my youth in that respect. They are much more concerned about their looks than we had to be back then. So many young people don’t have self-confidence nowadays.”

Sundström started writing as a child, in journals and diaries, and at some point in late adolescence started to feel that it was inevitable she would write a book. In 1966, she published Student-64, a novel of rebellious youth, and 10 years later came Engagement, her third novel and a huge and instant hit. Since then, she has written 14 further books, six of them for children, and in a tone of dismay wonders if becoming a novelist was perhaps a mistake. She is also a translator and found working alongside Kathy Saranpa, the English translator for the new edition of Engagement, an interesting exercise in learning to let go. (After the interview, Sundström emails to correct several English words she used and for which she has thought of more precise translations.)

“I’m very good at Swedish language, and I regret a bit that I didn’t devote my life to linguistics instead of literature,” she says. “It’s awful to say, but I don’t think literature is all that interesting. There are more interesting things in life. Language; etymologies; the developing of different languages.” In Swedish, the novel is called Maken (The Husband) and she wonders if “Mate” would’ve been a better title in English. “I learned that ‘mate’ was originally written with a ‘k’. So it is ‘make’, originally.” There is a puzzled silence. “But that doesn’t help.” Or, she wonders, “‘Uncoupling’: I think that would’ve been pretty adequate. Both as a criticism of the idea of coupledom, and also the problems of divorcing.”

Sundström herself has been divorced for 30 years and for the past few decades has had a romantic partner with whom she doesn’t live. “To me,” she says, “it’s the ideal; to be a couple, and to see each other when we wish, and still have our own lives. And not least because each of us has children with different parents. I never wanted to be a stepmother, and I didn’t want him to be a stepfather to my children because they had their own father.” Although, she adds, “I’m very thankful for the years I was in a family in the traditional way.” She recalls driving with her husband at the wheel and two children in the back thinking how lucky she was. “An ideal! And it’s me!”

This is a classic example of Sundström’s resistance to any one hard and fast position. She gravitates naturally away from political orthodoxy and believes – the translator’s curse, perhaps – there is always more than one way to see things. “By nature, I’m allergic to everything that is the truth of the day,” she says. “You know, everybody writes the same things in the papers. For example, the #MeToo movement; it wasn’t possible to make any objections in that discussion. I would never have said anything publicly then, but I didn’t feel quite happy about it; these demonstrations against the Swedish Academy [which awards the Nobel prize in literature], organised as a kind of feminist action. I felt very strange [about] all that; it seemed simplifying. All conflicts can’t be seen in that context.”

These are the ambiguities Sundström tackles so well in her fiction, where she can allow all the nuances absent in the headlines to play out. She created Engagement’s Martina as neither heroine nor cautionary tale, which is why she continues to be surprised at the fervour with which some young women take her up as a role model. A few years ago, she says, “I met a young girl who showed me her copy of Maken, and it was full of Post-its. And she said, ‘When I’m in trouble, or unsure of something, I think: what would Martina say?’” Sundström looks astonished. “I don’t know if I am supposed to be happy about that. Not for a moment was it my intention to propagate anything at all.”

Instead, she conceived of the book while going through a period of being single, wondering about the long-term prospects of any relationship, and thinking that, as the culture war around marriage and divorce in the 1970s took hold, it might be good grist for a novel. “In 1976 the Swedish king got married, and all of us radicals, of course, were republicans – I have been a member of the republican association for as long as I can remember. And although [regard for the monarchy] wasn’t as mad as it is in Britain, I really was depressed about people engaging with that bloody wedding. And me walking around feeling single.” She laughs. “This idea of coupledom is even more oppressing to young people today than it was in my day. That means it is very oppressing.”

We return to the subject of death. Sundström’s parents were unhistrionic about it too, she says. “My mother was a widow for five years, and when she was in hospital, I asked her: ‘Are you afraid of dying?’ And she seemed surprised at the question. ‘No! Why should I be?’” They didn’t talk about her being reunited with Sundström’s father, which is something, she notes disapprovingly, that people extend to their cats and dogs these days. “Imagine... what a crowd.” As it was, her parents, “were both so very calm, because they had lived in the conviction that this world isn’t the only one”.

This is not what Sundström believes. And yet, thanks to those admirable, religious people in her background, she sees the world much as they did, in terms of social engagement. If she was young now, she says, “I’d be a Greta Thunberg”. For Sundström, to look at the world and see potential for something better puts the novelist and the activist in a single category: those with the ability “to imagine something else than this world”.