Lily James reveals what she kept in her diary growing up

Actress Lily James has played the belle of the ball in Cinderella, been an action starlet in Baby Driver and is about to show off her singing chops in the much-anticipated Mamma Mia sequel, where she plays the younger version of Meryl Streep's character.

But, in her latest role as Juliet Ashton in The Guernsey Literary and Potato Peel Pie Society, the 29-year-old English rose plays a writer who uncovers a piece of British WWII history, which is still unknown to many people today.

Getting into the role of a writer is one the former Downton Abbey actress can identify with more than many might realise.

James reveals to TheFIX she grew up writing in a diary daily, right through till her second year of drama school in London.

"I wrote a lot of poems growing up," James admits during a chat with journalists in a London hotel room, adding her dad was a keen poet and her parents were the ones who made her write the diary.

Having them all stored in the attic of her family's home, James reveals she did recently look back at her efforts.

"Once I went through them recently and it was more about boys I fancied," she laughs.

Pointing out power of writing, James says in drama school they were encouraged to write down their goals and ambitions, which are "statistically more likely to come true" once in writing.

But the ever-modest actress says there was one thing she couldn't put down on paper.

"I don't think I could bring myself to write 'I want to win an Oscar' -- it just felt too obvious. So I tried to make them a bit cooler and more abstract but definitely one of them was to succeed as an actress, for sure."

James, who says she regularly has her nose in the pages of a novel on-set, admits she hadn't come across the book this movie is based on until after she landed the lead role, but "powered through it."

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"I love that it's written in the form of letters because there's something about putting a pen to paper to express what you feel, to get it down right and to give that to someone else. It's so poignant and purposeful unlike now, where you just sort of tweet something or Instagram something without thinking about it.

"This is something you’re actually committing to, therefore it's much deeper and more personal."

And while James is active on social media, she's been using it a lot less lately after smashing her phone, giving her time to get back to the simple pleasures.

"I don't have any apps on this, it's too old. So not Instagram or anything, and when you don’t have it, you read more. It's obvious and it's really sad."

Taking on a beloved character from a book that's sold almost eight million copies worldwide would be enough to intimidate many young actresses, but not James.

"You don't want to disappoint people but also the reason it's so beloved is because she's such a brilliant character," she tells TheFIX, adding proudly of Juliet: "She becomes such a bold courageous young woman."

And while James is certainly the leading lady in The Guernsey Literary and Potato Peel Pie Society, she is one of a stellar ensemble cast, featuring many other familiar faces from Downton Abbey, including: Penelope Wilton (Mrs Crawley), Jessica Brown Findlay (Lady Sybil) and Matthew Goode (Henry Talbot).

Gushing over working with Goode again -- who most recently played Princess Margaret's love interest in The Crown -- James says, "There's this sort of sparring [between their characters] and this banter that they have that felt very easy, and I kind of felt very at ease with him, perhaps 'cause I had worked with him before and also because of who he is. He's so hilarious."

Not content with one handsome co-star, James also has two love interests in the film, forming the ultimate love-triangle with Game of Thrones heartthrob Michiel Huisman and Hidden Figures hero Glenn Powell.

"I had three male co-stars who were all brilliant -- normally you're just stuck with one," she laughs.

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And it looks like the feeling is mutual with Powell telling TheFIX of working with James: "Lily is the leading woman you hope you get to work with forever, 'cause she's just awesome.”

"She's the sweetest. I think Lily is my mum's favourite leading woman that I've ever gotten a chance to work with.

"She's very kind, she's sensitive and really listens, there's no ego there… Sometimes in this business people get caught up in where they are in the pecking order and on the call sheet but she's a person that's always about the work, and also very self-deprecating," he adds, heaping praise on his co-star.

And get ready to see a lot more of this 'Dancing Queen', with Mamma Mia due out next month, and another musical in the works with Love Actually's Richard Curtis and Trainspotting's Danny Boyle at the helm.

"I have had this beautiful year last year, where I started the year doing Guernsey... and then I ended the year dancing to ABBA on boats in the middle of the sea and just total abandon," she laughs. "So, I've just had this beautiful year."

The Guernsey Literary and Potato Peel Society is out now in cinemas across Australia.