There is something unshakably mischievous about Patricia Clarkson. It’s as if she has a hipflask stashed in her handbag – her preferred method of self-help, she says, is bourbon – or a joint sneaked behind her ear. Maybe it’s the biker jacket, or the deep rasp made yet boomier by a cold (“My voice is usually below sea level, but now it’s just beyond”) or perhaps it’s the laugh – a long, hard cackle.

Clarkson does not do formal audiences. She is far more casual – conspiratorial, even. She perches on a sofa in a London hotel, tiny atop a great stack of cushions, discussing her new film, dishing out relationship advice (“Can’t you just be available? Isn’t that sexy and fun?”), bitching about Hollywood inequality and the passage of time. “I’d play your mother in a movie,” she says. “Kill me now!”

Yet, in her modest but charming new comedy, Learning to Drive, Clarkson is not just playing the mum. At 56, she takes the lead – a woman with a busy job and a prolific sex life – alongside her 72-year-old co-star Ben Kingsley.

“It’s two middle-aged people in a car; it’s Hollywood’s worst nightmare,” she says. “I actually had a producer once say, ‘Patricia, I love the script and I love you, but do you have to have all these scenes in the car?’”

That’s underselling it, but it’s true; a lot of the key moments in the film – adapted from a New Yorker article and directed by Isabel Coixet – do unfold in the ropey motor where Kingsley’s Sikh driving instructor teaches Clarkson’s workaholic literary critic the rules of the road. Despite the relative star power, it took eight years to get off the ground: a passion project for Clarkson who finally lands a leading role rather than being relegated to the sidelines, or even the scrapheap. Clarkson concedes that she is fortunate to be working at all.

She refers to it as “the vanishing act” – something that has afflicted many of her colleagues, while she has somehow remained ever-present, elevating standard-issue mum roles in Easy A, Friends with Benefits, Pieces of April and One Day; working with Woody Allen on Vicky Cristina Barcelona and Whatever Works; popping up in a franchise (as the villain in the Maze Runner saga), and perfecting the art of the sitcom cameo in Broad City and Parks and Recreation.

Clarkson stars alongside Ben Kingsley in Learning to Drive.

Photograph: Everett/Rex Features/Shutterstock

Yet while Clarkson is happy to be given these “beautiful” parts, she says, she still thinks of herself as “a leading lady”. And it appears that the industry is finally catching up with her. She is about to start work heading up a Sally Potter film with Kristin Scott Thomas, and has another planned with Coixet.

“I’ve been talking about this for 10 years now but with the true rise of art cinema yet again, it’s really made a dramatic shift in our stories about women of a certain age,” she says. “I love that we say women of a certain age and yet our lives are so uncertain. Well, mine is!”

Unlike many other female actors “of a certain age”, Clarkson has chosen not to make the handsomely paid move to the small screen to spearhead her own TV show about a feisty barrister or a sarcastic matriarch. Instead, she says, she seeks unconventionality on the big screen, something surprising among the glut of “desexed, matronly” roles she is offered.

“We always tend to want to soften female characters,” she says, referring to a previous complaint about a lack of unlikable women in film. “Well, unless it’s some ridiculous caricature like a dominatrix or a one-dimensional boss with no life and bad hair. These archetypal older women in movies can sometimes make my skin crawl. It’s about the one dimension, it’s about the lack of any texture.”

Clarkson, engaging as she is, doesn’t register as soft. She has played her fair share of mothers, but usually with a harder edge. It could also explain the longevity of her career, given her reluctance to accept the treatment that often befalls her peers.

“When I was younger, of course I had people act inappropriately to me,” she says. “I’ve had certain directors yell at me. But I didn’t stand for it and I didn’t let it go far enough for it to be in any way abusive to me. People didn’t speak up as much as they do now. Women have risen. But we’re still underpaid and we’re still a vast minority in this business.”

We broach the awkward subject of pay and the many female actors who have been vocal about the inequality that still exists in the industry. Eight years ago Clarkson discovered that a male co-star was being paid more than her. The imbalance, she says, was swiftly rectified. Did she demand it? “Absolutely,” she replies.

But with the shift in power comes a backlash. We discuss the largely male outrage at the female-fronted Ghostbusters reboot. A frustrated sigh comes from the cushions. She rolls her head back, prostrate on the sofa.

Clarkson with Rusty DeWees in Pieces of April. Photograph: Allstar/United Artists

“There are still so many movies made starring 50 men and one woman!” she says, half exasperated, half exhausted. “A white male actor should never be allowed to complain about anything. Shut up and sit in the corner. I mean, seriously! The odds of us having films made which star women … Everyone still references one movie: Bridesmaids! Ghostbusters is a great thing and I love these actresses. I can’t wait to see it.”

Is she concerned about the pressure on such a film to be successful? “Men make bad movies that bomb all the time but they’re like, ‘Oh, well, we didn’t do the marketing right,’” she says. “Eat me!”

I tell her about the complaint of one white male actor, Game of Thrones star Kit Harington, who expressed disappointment at what he sees as a sexist double standard in the industry, saying he’s sick of talking about his hair and his body. “He’s a sex symbol,” Clarkson scoffs. “Get over it. You have an amazing career and you’re on a hot show. Take your shirt off.” More of that cackle.

Clarkson’s loose-cannon independence is also reflected in her personal life. “Being married and having a child was not something I wanted and I knew that at a very young age,” she says. “I tend to be more solitary and I’m truly a free spirit. I like a life that’s unpredictable. Even though it can take a toll on you in ways that are hard to express.” She’s proud not to “rely upon a man at all” and believes that the life she has chosen frees her from “the restraints or the pressures that people have who are married or raising children”.

She is also unafraid of speaking out politically, was vocal about gay marriage before the legislation was passed, and the effects of the Deepwater Horizon oil spill. She gets predictably, happily animated when talk turns to Donald Trump, and his attitude to migrants.

“I find it hard to even engage in any conversation about this,” she says. “It seems so antiquated and offensive on every level. It’s beyond comprehension to me that we would for any moment at any time be anti-immigration. The world is in chaos and we’re here to talk about a movie!”

We are – it’s true. We step back to safety and discuss sex (“always a good topic”), in particular the sweaty tantric marathon in Learning to Drive: “I just said, ‘I don’t know what you’re going to do. Just as long as you don’t hurt me. Let’s just go.’”

It’s something of a motto. Hollywood remains a challenging environment for women over 50 whose names don’t begin with Meryl, but Clarkson refuses to be defeated, or even to look back in anger. “I’ve taken people’s seconds before and they’ve turned out to be some of the greatest experiences of my life,” she says. “I probably should have more regrets. But I don’t.” And she cackles again, ever cheerful, ever sanguine. No hipflask, none needed.

Learning to Drive is released in the UK on 10 June