Somewhere in the middle of Poly Styrene: I Am a Cliché is a clip of punk’s brightest ingénue interviewed on television in 1978. We see Styrene’s smiling face in close-up. Tony Wilson, one of the most influential pop journalists of the day, introduces her: “With those braces on her teeth, Poly Styrene is hardly Linda Ronstadt.” Styrene’s reaction is captured in slow-motion; we can almost see the confidence draining away. She was 21.

“It is one of the saddest but most impactful moments of the film,” says Celeste Bell, Styrene’s daughter, and co-writer and co-director of the new feature-length documentary charting her mother’s life and artistic legacy. “There was a lot of comparison with other female artists who were more sexy or conventionally beautiful. She was a young girl, very young. It had a huge effect on her self-esteem . . . and it continued to affect her throughout her life.”

Styrene, vocalist with punk band X-Ray Spex, was the first woman of colour to front a successful British rock band. She died in 2011 but her sharp songwriting, self-imagined stage performances and refusal to conform to conventional beauty standards (metal teeth braces, unsmooth hair, battle-clothes) shine out in the history of women in music.

Her lyrics for X-Ray Spex, particularly those of “Oh Bondage Up Yours!” and “Germ Free Adolescents”, were social commentary that cut through a morass of fighting punk anthems in the 1970s and are still relevant. Her style and influence are detectable in artists from Björk to Billie Eilish to FKA Twigs.

A prolific songwriter, poet and diarist, she also designed the band’s costumes and record-sleeve artwork. As one contemporary says in the film: “She was the best of punk.” But fame, public scrutiny and its aftershocks cost Styrene her mental health.

Styrene formed X-Ray Spex at 19 after seeing the Sex Pistols perform on Hastings pier in 1976. Less well known is what happened to her before and after she was famous.

Bell, Styrene’s only child, was born in 1981, two years after the band split. She inherited archives — “things of value and cultural importance” — and in 2019 they formed the basis of a book and an exhibition. Now, the project has grown into a documentary backed by a crowdfunding campaign, private investors and with support from Screen Scotland and Sky Arts, among others. This month, Poly Styrene: I Am a Cliché will premiere online as part of the Glasgow Film Festival, and in the US in March at the SXSW Film Festival.

“There was that nagging feeling: would she have hated this?” says Bell. “Because my mum was always a very harsh critic. That was a big responsibility for me. And I do feel the longer the project went on, the more it developed, it’s become more and more and more like the film she would have wanted.”

Co-directed by British-Chinese Singaporean director Paul Sng, whose previous work includes the 2015 documentary Sleaford Mods: Invisible Britain, the film combines rare footage with Bell’s narration, as she retraces her mother’s travels from the UK to New York to India. There is commentary from friends, family, fans and cultural critics. Oscar-nominated Irish actress Ruth Negga narrates Styrene’s diary, lyrics and poems. Negga has perfected Styrene’s fragile south London lilt.

But it is not just a music documentary; the film also attempts to put Styrene’s creative energy and erratic mental health into context. And there are reflections on a difficult relationship between parent and child.

“We used diary entries as the starting point, and we were building from there, tying them into my memories,” says Bell. “Then interviewing people who knew her, or who were inspired by her to complete that picture. It wasn’t a linear process. I started at the end of my mum’s life, writing my narration, and worked my way back.”

Forming a coherent narrative from boxes of paperwork, the remnants of a sometimes chaotic life, was a challenge for Bell and the production team (Styrene frequently changed her name, for example), but it also helped Bell to demystify her mother. As she says in the film, Styrene’s years of fame were “far removed from the mother I knew”.

Styrene was born Marion Elliott in 1957 in south London to an English mother and a largely absent Somalian father (she later added his surname to hers, becoming Marianne Elliott-Sa’id). Her mixed racial heritage was unusual in 1960s London, and her Brixton childhood was tough. Marion struggled to fit in with the local West Indian children, and she encountered hostility from white contemporaries: “They see us as a threat to their genetic existence,” she wrote in her diary.

Punk was “full of people nobody else wanted”, as contemporary and fellow south Londoner Rhoda Dakar of The Specials says in the film — and Styrene fitted right in. But fame troubled her: she was hospitalised, misdiagnosed with schizophrenia (she had acute bipolar disorder), and the band split at the end of the 1970s.

Five years later, she moved with the young Celeste into the Hare Krishna temple at Bhaktivedanta Manor, housed in a mock-Tudor mansion in Hertfordshire which was donated to the movement by George Harrison. Bell remembers the temple as “like a little village” and that Styrene “was caught up in her new faith with a fervour that veered towards extremism”. She changed her name, becoming Maharani.

For the film, Bell had less source material to draw on for the Bhaktivedanta years, and in part relied on her own memories. “It was a happy time, Utopian. We lived in a beautiful place, a beautiful country estate in a real community, and I lived there and went to school there and we had total freedom to play and explore.

“It was wonderful in many ways. But that obviously has a flip side, because you are cut off from the world. And my mum was unwell a lot.” Styrene’s increasingly erratic behaviour led to the young Celeste moving to live with her grandmother. Later, Styrene made a successful musical comeback before her death, and she and Bell were close for many years.

The richness of Styrene’s archives lifts the film above many biographical documentaries. Bell, a Barcelona-based language teacher and musician, says she was “thrown into” the task of managing her mother’s legacy: “I understood quite quickly that this was a job that I would always have to do.”

The film’s title is taken from a song, but Styrene was anything but a cliché. So why did Bell choose it? Like Styrene, it is subversive: “Mum’s art was about taking something banal, ordinary, and then turning it on its head. And it becomes something spectacular.”

The stage name was one example: Styrene found it in the Yellow Pages. Costumes were another: “Granny-chic from the ’60s, military outfits from army surplus stores, all with a futuristic aesthetic”, as Bell describes them.

In clips of stage performances, wearing neoprene pinafore, military helmet and goggles, Styrene looks like a subversion of a futuristic ’60s Pierre Cardin model. Space-age chic is loosely interpreted with second-hand gear on a black woman with teeth braces. It is radical, wry and very postmodern — in Styrene’s words: “a send-up”. Looking like herself was a radical act then, as now.

Bell sounds like Styrene, with the same steady, precise pace and south London inflections. She also shares her mother’s ability to articulate, but seems much more confident and assured.

“My mum was always saying, I’m not special, I'm not remarkable, I’m ordinary,” she says. “But there was something extraordinary in that.”

Available to stream via Modern Films from March 5, modernfilms.com/watch. Glasgow Film Festival, February 24-March 7, glasgowfilm.org