A gaggle of teenage girls lark about on the rooftop of an estate in east London, singing, rapping, dancing and laughing. The Gherkin looms behind them, as it did over the drug dealers of Top Boy. Rocks, though, is knife-free and very much a female-led piece, in front of and behind the camera. The Bafta-winning director of the film, Sarah Gavron, could have called it Top Girls if Caryl Churchill hadn’t beaten her to it. Yet that would imply a sense of competition that this raw and vivid story just isn’t interested in. As a depiction of British girlhood it’s up there with Fish Tank and My Summer of Love, but in Rocks the coming of age has nothing to do with sex.

The themes here are the burdens of responsibility and the spectrum of female friendship, from silly to serious. “Real queens fix each other’s crowns,” reads a poster on a bedroom wall. That rooftop scene is one of several group sequences that fizz with unruly naturalism. “Hey, Sasha, what’s your body count?” one girl asks another across a crowded playground. Later there’s an epic cake-mix fight in a home-economics lesson.

The standout member of an impressively fiery and mostly untrained cast is Bukky Bakray, 17, who plays the title role with a mixture of chutzpah and fragility. When her mentally ill single mother walks out, 15-year-old Rocks has to look after her seven-year-old brother on her own. The envelope of notes left by her mum soon becomes empty. Lying and thieving start to tempt.

“We wanted to make a film about the kind of girls that you don’t see on our screens, but you do see in our streets and in our schools,” says Gavron, who is best known for her adaptation of Monica Ali’s Brick Lane and Suffragette, starring Meryl Streep. “But we thought, ‘Let’s build that with them.’” She and her team scoured inner-city schools in the east and north of London, meeting more than 1,200 girls and inviting them to workshops. Six months later they had a core group of about a dozen, from a variety of backgrounds: Muslim, Christian, west African, east African, Polish gypsy. “It became impossible not to be completely enamored by their stories and their energy,” says Anu Henriques, the associate director of the film, who has joined Gavron on the Zoom call in an effort to emphasize its collaborative nature.

All of the girls were in their mid-teens at the time of filming. A pivotal age. “Just transitioning from child to adult,” Gavron says. “They can be seen quite often as adults, particularly Bukky, who’s quite tall, but she’s still a child.” Bakray’s experiences as a Nigerian-British girl growing up on an estate in east London chimed closely with those of the film’s co-writer, Theresa Ikoko. “Theresa talks a lot about how Black girls particularly have to shoulder responsibilities beyond their years,” Gavron says. “They’re strong, but they’re also soft and vulnerable.”

When it came to making a film such as this, Gavron was aware that she did not have authenticity on her side. “Sarah knew from the start that as a middle-class white woman she could not be the one leading this story,” Henriques says. Hang on, though — she is the director. “But it’s not like I own the film,” Gavron says. “It’s not like I wrote it. It’s really been a difficult thing to stop it getting billed as “Sarah Gavron’s Rocks”. That seems so disingenuous to the whole spirit of it.” How many male directors would go that far?

In 2015 Gavron was criticized during the promotion of Suffragette in America when members of the white cast, including Streep and Carey Mulligan, wore T-shirts reading “I’d rather be a rebel slave than a slave”. Wording that understandably jarred with some. “It was such a complex picture because we were promoting a film in America where the suffrage movement had been riddled with the most horrific racism, and we were making a film about the UK movement,” Gavron says.

Was that experience in the back of her mind when she made the much more diverse Rocks? “It was a little bit inspired by Suffragette — thinking what it’s like to be a young person growing up now, a hundred years later. The industry has changed in great ways since, just thinking about Armando Iannucci’s David Copperfield and the ways that casting has broadened.” The idea on Rocks, Gavron says, was to create “a very kind of unfilm-y atmosphere.” There was a script, but the actors were encouraged to depart from it. “We wanted to give them the freedom to express things in their own way. We didn’t shout ‘action’ or ‘cut’ in the normal way. We rolled two cameras all the time; we had a 75 per cent female crew who were largely young and from some of the same communities that the kids came from. We wanted them to feel they could fail, they could try things.”

It was a risky strategy, giving so much power to novice performers, but it paid off handsomely. Although the actors started off as strangers, friendships began to form and influence the performances. “They were getting to know each other, pushing and pulling at each other,” Henriques says. “I don’t think there was anything manufactured — whenever we did try and manufacture it, it was absolutely awful.”

Bakray and her fellow cast members had sensitive bullshit detectors and weren’t afraid to let them beep. “They didn’t hold back because they knew what was truthful,” Gavron says. They were shooting a scene in a classroom when Kosar Ali, who plays Rocks’s ballsy best friend, Sumaya, asked to speak to Gavron. “She said, ‘It’s dead, it’s totally dead. We just wouldn’t do it like this.’” The director had them sitting dutifully at their desks — more Jean Brodie than Hackney. Ali said they would be out of their chairs, moving around the room. “And she was right,” Gavron says.

The result is a film that mirrors the lives of its cast as few have, if any. “I saw a lot of Eighties movies in my teens and they were mostly Tom Cruise and I just thought that was the world of films: white men who were quite buff,” Gavron says. “It was like an epiphany for me when I started to see films directed by women, that centred on women. The same epiphany is happening for these girls. They just haven’t seen people like them on screen.”

It was the unlikeliest of friendships that reignited Craig Foster’s passion for life. Feeling a loss of purpose, the South African film-maker found a boost from taking daily free dives in the icy Atlantic waters near his home in Cape Town. Instantly fascinated by the wonders of the dense kelp forests that fringe the coast, he was drawn into the routine of a young female octopus that became his guide to an underwater world “more extreme than our maddest science fiction”.

She made the first move in this improbable rapport, he said, as she became accustomed to his presence and began displaying signs of recognition. As her curiosity was piqued, she began tentatively exploring him with a suckered arm, keeping the rest of her body secure in her den. Then, one day, she did the last thing Mr Foster, 52, expected of an animal whose kind has survived for millions of years through acute caution. “She came entirely out of her den and wrapped all her arms around me,” he told The Times. “It was an incredible moment to realize there was full trust there and she was allowing me into her secret world.”

In the months that followed she offered him a unique understanding of the perilous life of the most intelligent of all invertebrates, and a new appreciation of his own. He never gave the octopus a name. “I didn’t want her to become my pet. She was, in fact, my ultimate teacher,” he said.

The development encouraged the film-maker to pick up his camera to document what he knew would be a fleeting connection, as the average life expectancy of a common octopus is little more than a year. In the resultant documentary, My Octopus Teacher, which is being shown on Netflix, she displays her myriad tactics to outwit predators, including some that have never been recorded on film or by scientists; all self-taught, since octopuses are never parented.

A particular highlight for Mr Foster was capturing what is thought to be the first recorded case of playful behavior in a wild cephalopod as she encounters a shoal of passing fish. At other times he struggled to watch nature take its course, notably when a pyjama shark clamped the octopus in a “death roll” before swimming away while eating one of her arms. A tiny camera she allowed Mr Foster to place in her den intimately captures her recovery, and the growing back of the arm over the next 100 days.

On another occasion, the octopus is seen outfoxing a shark by using her 2,000 suckers to create an instant cape of “shells”, and later attaching herself to the back of the predator before eventually drifting away to safety.

On the day Mr Foster saw her mating, he realized it would start the clock on the end of their encounter. “I knew that she would be timing her death for the hatching of those eggs,” he said. After laying her clutch of eggs a female octopus stops eating and wastes away.

Of all the natural phenomena that Mr Foster has recorded during his life, including from the lair of a crocodile and tracking with the Khoisan people in the Kalahari desert, his time with the octopus had the deepest impact. “It was a special intimacy with her, an experience I never expected to have and it taught me how inseparable we are from nature,” he said. “Her life was so hard, so complex and so beautiful. She gave me a profound lesson about my own humanity.”