For a bona fide legend of British film-making – 1980s avant-garde experimentalist turned studio-friendly darling of the arthouse scene – Sally Potter is less hymned in her homeland than she should be. Then again, hers has always been a quiet, steady presence on the cinematic landscape rather than one which powers its own reputation through spectacle or self-publicity. But cast an eye over her back catalogue and you wonder why her status as a trailblazing female director isn’t etched onto a plaque somewhere.

It’s quite a CV. In her 1983 debut The Gold Diggers, shot with an all-female crew, she worked with 1960s legend Julie Christie. She made a film about tango, shot another film in verse and in 2000 cast Hollywood A-listers Johnny Depp, Cate Blanchett and Harry Dean Stanton in The Man Who Cried. In 2009 she shot Rage with Jude Law and Judi Dench, and in 2012 she made Ginger And Rosa, casting a 13-year-old Elle Fanning as a 16-year-old British girl in a 1960s coming-of-age tale. In 2017 she turned back the technological clock to shoot The Party in gorgeous black and white. It had Bruno Ganz, Timothy Spall, Cillian Murphy and Kristin Scott Thomas in its strong ensemble cast.

And let’s not forget Orlando, her 1992 adaptation of Virginia Woolf’s famous novel, which starred Tilda Swinton (who else?) in the title role of the gender-shifting time traveller. Nearly 30 years on, Orlando continues to influence fashion and inform discussions on everything from sexual politics and gender identity to representations of history and queer culture.

“I am proud of that film,” says Potter over a Zoom call. “The whole thing was a work of crazy ambition, but I had a very willing and wonderful collaborator in the form of Tilda Swinton. It was an amazing adventure and none of us knew – well, I certainly never knew – if anyone was ever going to like it or relate to it. Its deeper themes possessed me, though. The themes of immortality, class and gender are very rich themes to mine.”

Although she always writes her own scripts, the variety of themes and styles on display in Potter’s four decades of film-making is jaw-dropping. But there are constants, too, and one is her clear love of, and respect for, actors.

“It’s not true of all directors,” she admits. “I get very close to actors, I have a great respect for the work, I see it as a sort of sacred profession that goes back a very long way. I’ve had pretty much universally great experiences working with actors and I think they know that I love working with them and collaborating together. They respond to that very strongly.”

Another constant is her love of constraints. Yes, from 2004, was delivered almost entirely in iambic pentameter (“an interesting experiment, but a movie it ain’t,” complained The Washington Post). Meanwhile Rage, released two years after the launch of the iPhone, was intended to be viewed on smartphones.

“Every film has constraints, but sometimes to voluntarily set constraints is sort of liberating,” she says. “In the case of Rage, which was designed as a miniature to be used on phones, it was about five years ahead of its time because there wasn’t actually the technology available then to allow people to stream to their phones. People told me ‘Oh it’ll never happen, it’ll never take off, Sally. Nobody’s ever going to watch a film on their phone’. Ha ha.”

Potter’s new film is The Roads Not Taken. It’s chronologically tight, taking place over just 24 hours, and the plot is sparse to the point of non-existent: New Yorker Leo visits the dentist and the optician in the company of his daughter Molly. But it is unusual in being one of the most explicitly personal she has ever made because Leo suffers from a form of early-onset dementia, the same condition which affected Potter's younger brother Nic, bassist in 1970s prog rock band Van Der Graaf Generator. He died in 2013 aged 61.

“For several years I had been exploring the idea of parallel lives, the point where you arrive at a crossroads and you take one direction or the other,” she explains. “As your life keeps branching and branching, are all these possible selves somehow out there, or in the head? So I got very fascinated by that idea. In parallel with that, in my own life, my younger brother, who I dearly loved, got a form of young onset dementia.”

The Bohemian siblings, children of a music teacher and a poet, were close in age and in spirit. After Nic's diagnosis, Potter spent a great deal of time caring for him “and protecting him, really, as I witnessed the not always good ways he was treated as he got more ill and finally died. It was in the aftermath of that that these two ideas coalesced and I went on the journey of deciding to try to work with some of the observations I had of him.”

The idea wasn’t to make a straight portrait of her brother, however.

“The character who emerged finally is utterly different from my brother but it’s grounded, let’s say, in the understanding I had both of his condition and what it was like to care for somebody who had that condition and love them.”

In The Roads Not Taken, Leo is played Javier Bardem and in Potter’s hands he becomes a Mexican author who long ago emigrated to the US. Elle Fanning, now an industry veteran yet still only 22, reunites with the director to play Molly.

Sparse the surface action may be, but what occupies much of the screen time is Leo’s interior visions. One is of an earlier life in Mexico, where he is married to Dolores (Salma Hayek) but refuses to join her at a Day of the Dead commemoration to mourn their dead son. Another is of a later writing sojourn in Greece where he has an encounter with a young German woman who persuades him to return to another wife, American wife Rita (Laura Linney), and to his infant daughter (Molly, of course).

But as much as The Roads Not Taken is a film about dementia, it is also a study of the fortitude of those people, often women, who care for dementia sufferers.

“I’m very aware of the often hidden role of women as carers, whether that’s as mothers of children or daughters of ageing parents or, in my case, a sibling,” Potter says. “Some people call it the burden of care but it can be entered into with great love. It’s not necessarily given with resentment, but nevertheless it’s tough … In that sense Molly is just as important a character as Leo even though we spend more screen time with Leo as he moves through these parallel possible selves.”

Sally Potter turns 71 next weekend. She acts (and looks) at least 10 years younger, so there’s little likelihood of The Roads Not Taken being her last film – and, if the next decade is as productive as the last, it would be a rash person who bet against her throwing out a few more stylistic curveballs. But if she was starting out in the industry today, would things be harder or easier? She doesn't even have to think about it.

“Easier. It couldn’t be harder than when I was starting out. There just were no other female directors. It was very tough at the beginning. Not that it’s always easy now – with every film you have start from the beginning, raise the money – but I think if I was starting out now it would be cheaper. All you need is a phone and an idea and you can make a film.”

You don’t even need a cinema in which to show that film necessarily, which is perhaps just as well. Potter isn’t overly optimistic about the future of theatres. “With the pandemic and the problem of the big collective experience right now I’d say cinema has a bit of a full stop after it. Not entirely. People are going out again. But it’s not as it was.”

There will always be a thirst for stories, however, and for Potter that’s where the adventure lies.

“There’s no longer this thing called film and this thing called television,” she says. “It’s all part of a great, fluid way of working with storytelling and the moving image. So if we can be adaptable and flexible at every stage, anything can happen. The real struggle is not the form, the real struggle is what stories are worth telling and in what way.”

The Roads Not Taken is out now