With her chestnut waves and English rose sensibility, it is no wonder that Lily James made her name at a time when period dramas and corseted costumes were suitably en vogue. And when Downtown Abbey fever had subsided, the Esher-born actress garnered more acclaim for her starring role in the live-action version of Cinderella, and her supporting role alongside Academy Award-winner Gary Oldman in Darkest Hour, last year’s historical Winston Churchill biopic.

That’s not to say, however, that James is formulaic. Her other notable 2017 release was Edgar Wright’s pop-art crime flick Baby Driver – a film somewhat undermined by allegations made against its star Kevin Spacey. But, for James’s part, Baby Driver represented a move into a new arena of film: bold, modern, American. It’s a sentiment with which the 29-year-old agrees: “I was ready for something different.”

True to her word, James’s latest project is quite possibly as far removed from the lofty halls of Downton Abbey or the dank stringency of the Churchill War Rooms as can be. But having worked in the past with a host of Hollywood’s biggest names – from Cate Blanchett to Gary Oldman and Christopher Plummer – it seems only right that James will now link up with an ensemble cast of mega-watt proportions.

If playing a younger incarnation of Meryl Streep’s character Donna, alongside Pierce Brosnan, Stellan Skarsgård, Julie Walters, Amanda Seyfried, Colin Firth and Cher wasn’t enough, doing so in sun-drenched Abba sing-a-long sequel Mamma Mia! Here We Go Again is certainly a move in a more musical, summery direction. To the outside observer, it appears a simple career choice, but for James the chance to belt out some classic tunes is far more personal.

“I always loved singing; I’m not really sure why I stopped,” the Guildhall School of Music graduate reveals. “It’s always been my dream to play a singer on screen, someone like Janis Joplin. Perhaps I spent so long focusing on ‘serious’ roles that I immediately discounted doing musicals – but that has changed now.”

The chance to brush up on her pop classics alongside arguably the finest actress alive is surely a draw too. Indeed, while James hoped to eschew the unimaginable task of emulation in favour of “doing something new” with Streep’s character in her formative years, there’s a palpable sense that, for James, just being on the same set as the trailblazing Tinseltown legend was enough for her to soak up some valuable experience. “Just before I was about to meet Meryl I heard her singing,” recalls James. “I had to tell myself to pull it together. Honestly, I was about to cry!”

As James’s career continues to soar, she remains in debt to her recent education of working alongside some of the biggest names in cinema. “I’ve been impressed by the way they always remain very cool and composed in all situations,” she recollects. “It’s one thing to stay focused on the set and be very present doing your scenes – I’ve been able to witness that with Cate Blanchett and Meryl Streep. But one thing that has struck me even more is dealing with the public and everything else surrounding the business.

“I remember one time when Cate Blanchett, who played my stepmother in Cinderella, arrived for an event and she literally had to walk past hundreds of photographers screaming at her. She still maintained her poise even though she had to deal with all the chaos around her. That taught me that you need to be able to be mentally tough and self-confident to deal with success and not let yourself be intimidated by the attention.”

In James’s case, there is an obvious desire to stay tight-lipped about private matters – especially her four-year relationship with former Doctor Who and The Crown star Matt Smith. But even the most obsessively protective celebrity can still experience the drawbacks of fame. “Sometimes it’s odd to see photos taken of you by the paparazzi when you had no idea you were being photographed,” she admits. “It’s also difficult to be away from home a lot. I had to give away my cat a while ago, even though I was obsessed with her, because I was never home. I never grieved though, about giving her away, and my boyfriend said I was really cold! I still see her when I visit the friend I gave her to.”

Yet in spite of her undeniable luck in collaborating with outstanding co-stars from the start, there’s always a sense that James was destined to take centre stage soon enough. Her father, James Thomson, (from whom Lily takes her professional surname), passed away in 2008. An actor and poet, he remains “inspirational” to his daughter, who is now the third generation of the family to go into showbusiness.

“My grandma was an actress and my dad did some acting when I was younger,” she says. “I never really gave it that much thought. I didn’t live and breathe acting although I was really into musicals, but I didn’t know anything really about how the business worked or what an agent did. I was obsessed with films and I still am. I love watching brilliant actors and sometimes that makes me wonder ‘how do they do it?’ which sometimes distracts me from just being able to sit back and enjoy a film without thinking too much.”

James reminisces about her family members’ earlier careers, which may have contributed to her success. “One day I hope to collect all of my father’s stories and have them published,” she smiles. There’s no denying that contemporary Hollywood is far removed from the world in which she grew up, but with her close-knit support network, desire for privacy and track record of taking on new and challenging roles, James may well fashion herself into one of Britain’s most talented acting exports, even in today’s media-driven society.

“I don’t think so,” she muses, when asked if fame has had an impact on her life. “I feel the same and I don’t think it’s changed the way I behave with my friends or affected my thinking about the kind of life I want to be able to lead. I’m the same person I’ve always been.

“But I still really don’t understand what’s so great about a photo of an actor buying milk! And then my grandmother sees the photos in the newspaper and asks me with a very worried look: ‘Why do you always have holes in your jeans?’”