Lina Wertmüller’s first job in film was to scout out interesting faces for Federico Fellini. The Italian master was at the height of his success; she was an ambitious young puppeteer more interested in snatching her own location footage than honouring the duties of an assistant director. “I was the worst assistant, but that was overlooked because I was likable,” she says.

The film was 8½, the tale of a fecklessly promiscuous director abandoned by his muse. It wasn’t long before Wertmüller had cast her own mother and her card circle of elegant socialites, who went on to be fleetingly immortalised playing canasta on a beach, in the 1963 film listed by Sight & Sound as the 10th greatest of all time.

By the end of that year, Wertmüller had made her directorial debut with I basilischi (The Lizards) – about three aimless youths in a sleepy southern Italian town – and embarked on her own lifelong pursuit of faces, bodies and dialects that could not easily be sourced from Cinecittà (Italy’s central studios).

Now aged 90, Wertmüller is about to arrive in London, on screen if not in person, as the first star of a new strand at London’s Barbican celebrating neglected film-makers. Four of her films will be featured in the month-long season, alongside a perky documentary about her life directed by her protege and assistant Valerio Ruiz. It is Ruiz who greets me at her apartment, perched two storeys up a winding staircase around the corner from the Piazza del Popolo in central Rome.

The door opens on two lifesized cloth dummies – featureless apart from their carefully tailored genitals – which sprawl across a bench in the entrance hall. Wertmüller is reclined on a chaise longue, a diminutive figure in her trademark white-framed glasses, with glossy scarlet toenails peeping out from a loose black robe. She shifts enough to allow me a perch on the end next to her feet, but is clearly not going to be separated from the two props that will dominate the next hour: an ashtray, into which she taps the ash from a steady stream of cigarettes, and an antique telephone, which she answers at length, each of the several times it rings.

Her attention is focused beadily outwards: “And where did you grow up?” she parries, in answer to a question about her early life. “How tall are you?” she demands later, creating the alarming impression that I might be being sized up as an extra for her next film. When I tell her I have spent the last week immersed in her work, which I found impressive but also deeply shocking, she takes a deep drag on her cigarette and gives the first of many exaggerated shrugs.

The four films that will be shown in the retrospective were released in an intense bout of creativity in the early 1970s, culminating in Seven Beauties, which won four Oscar nominations in 1977, making Wertmüller the first woman to receive a best director nomination (it wasn’t until 1994 that Jane Campion joined her, for The Piano). Her Oscar nominations (she also received a nod for best screenplay) opened the door to a brief affair with American cinema. In the documentary, Behind the White Glasses, her lead actor, Giancarlo Giannini, recalls strolling together through New York’s Times Square beneath billboards for four of their films.

With their polemical ardour, their gross-out caricatures – usually of women – and their frequent outbursts of sexual violence, it is hard to imagine such films even being made today, let alone screened in Times Square. But just as important, at the time, was their social specificity. Three of the Barbican quartet deal directly with the stand-off between socialism, fascism and crime in mid-century Italy. Though Wertmüller was a socialist, she was too shrewd, cynical or capricious (depending on your perspective) to suggest that the gordian knot could ever be untangled.

In the most overtly comic of them, 1972s The Seduction of Mimi, a young activist is forced to leave his home in Sicily after voting against the mafia in the naive belief that the ballot would be secret. In 1973’s lingerie-tastic Love and Anarchy, an accidental anarchist hides out in a brothel and falls in love with a prostitute, while waiting to assassinate Mussolini. In the grimly comedic Seven Beauties, a young Neapolitan hoodlum (nicknamed “Settebellezze” – seven beauties – because of his disfiguring freckles) ends up in a Nazi concentration camp after deserting the army to which he has been conscripted after a series of mishaps prompted by the accidental shooting of his sister’s wealthy sugar-daddy.

In all three, Giannini plays variations on a hapless everyman. In each, Wertmüller (who wrote all her screenplays) immerses him in scenes of breathtaking sexual abuse – most shockingly in Seven Beauties, in which he rapes a straitjacketed woman in a mental hospital before being forced into sex with a grotesque Nazi camp commandant.

All three also feature cameos from one of Wertmüller’s most striking outsider actors, Elena Fiore, who made her debut in The Seduction of Mimi as a middle-aged Sicilian housewife, her colossal, dimpled buttocks filmed in unforgiving closeup, as if through Mimi’s horrified eyes, as she succumbs to his cynical advances. When I suggest that it must have been pretty brave for an actor to agree to such unsisterly camerawork, the director gives another of her histrionic shrugs, and says: “I am looking for a reality that deforms the body.”

So who is Lina Wertmüller and what drives her “deforming” vision? Archangela Felice Assunta Wertmüller von Eigg Spañol von Braueich – to give her full birth name – was born into a wealthy family with a lineage that stretched back to Switzerland, via a couple of generations in the southern Italian region of Basilicata.

Those bare facts, she suggests, explain two things: first, her attachment to the south of Italy, even though she has spent much of her life in Rome. And, second and more playfully, her predilection for long titles (the Italian title of Love and Anarchy is Film d’amore e d’anarchia, ovvero: stamattina alle 10, in via dei Fiori, nella nota casa di tolleranza ...). They combine into an aristocratic disdain for petty conventions dictated from the powerhouses of the north. “The titles were also perhaps a joke at the expense of my producers, who had to fit them on a billboard.”

Expelled from multiple convent schools, Wertmüller abandoned her studies at 16 for a drama college, where she became immersed in the Stanislavski tradition. One childhood friend went on to marry the actor Marcello Mastroianni, thereby manoeuvering Wertmüller’s introduction to Fellini. In between, she immersed herself in popular theatre and worked for a travelling puppet troupe. “Really, there are two strands – two souls – which coexist in my work: the lighthearted one associated with musical comedies and the more socially conscious one,” she says.

Her most recent, and probably her last, job was as co-director of Verdi’s opera Macbeth, at Salerno in 2016. But her rackety “vulgar” side is captured in the documentary when she performs one of her own songs, Bac Baccanale, written for an abortive musical about Caligula. “Hands, sighs, butts, bellies … horny girls all in a frenzy …” she growls, lit up with a ribald energy.

The final film of the Barbican season, 1974’s Swept Away, condenses the elemental struggles of class, sex and geographical origin into a fable of a rich woman and a poor sailor marooned on a desert island. It is Wertmüller’s Lord of the Flies, with the exquisite Mariangela Melato gradually succumbing to Giannini’s re-emerging south-Italian machismo. “They are not only a man and a woman but they represent two politics: communist and capitalist. I was interested in observing what their relationship could be with no laws,” Wertmüller says.

Sexy and reprobate, Swept Away was picked up by Guy Ritchie and Madonna for a poorly received remake in 2002. In the aftermath of her Oscars success, Wertmüller was signed up by Warner Brothers for four English language films, but the deal only survived one flop. The film critic Derek Malcolm recalls “a very curious case … In the early and mid-70s, she was the toast of Rome, London and New York, but quite suddenly, in the late 70s, the bubble seemed to burst. After getting that rare Academy nomination, she could do nothing right.”

“Italy is not one but many countries,” she says. One possible explanation for her seesawing fortunes is that her work was so intricately bound up with those countries, as reflected in the faces and speech rhythms of their inhabitants, that it got lost in translation. Her portrayal of women also fell foul of feminist critics. “Wertmüller’s detachment from her own femaleness and her old-style sense of herself as superwoman allows her to treat women with more exaggerated scorn, even loathing, than men would dare to,” wrote Barbara Quart in 1988 – an accusation that 30 years on, earns another shrug from the director: “Critics will say what critics say. I have never been concerned with success.”

“Directing is always an adventure, an adventure which can be good or bad and you can use this testament of yours to add something or nothing,” she says in the documentary. “We added something: the face of the south which few knew about.” In Swept Away, as in so many of her films, rape generates love. Is she really suggesting that sexual humiliation is erotic, that violence is the only way the different Italys can be reconciled? “Love is a mystery,” she says. “Why is love born? Because it is born.”

• Love and Anarchy: The Films of Lina Wertmüller is at the Barbican, London EC2, until 31 March