It's not that Romola Garai collects top directors, but she has, at just 27, worked with more than seems a reasonable share of them, including Michael Apted, Kenneth Branagh, Woody Allen and Richard Eyre. The latest is Stephen Poliakoff, in whose hugely acclaimed film Glorious 39, about the run-up to the Second World War, she has a key role as the adopted daughter of an appeasement-supporting Tory politician (Bill Nighy). Her character plays witness to a section of Britain's comfortable upper middle class and its attempts to avoid war – and, as it happens, protect its own privilege – at all costs.

Garai, of Jewish-Hungarian stock, lost most of her recent forebears in the Holocaust – there are no known family ties left in Eastern Europe – so it is unsurprising that she shares her director's passion that this lesson not be forgotten. "Stephen is a Russian Jew, and this film is a sort of a comment on the Holocaust through visual metaphors. I was able to connect with his passion."

The anxiety of Garai's character as the story progresses is unsettling. Her performance rekindles memories of Ingrid Bergman in Hitchcock's thrillers. Poliakoff fought to get her the role ahead of better-known actors – "I'm not a financial draw," she admits – and her performance has led to comparisons with Kate Winslet, at which she blushes, embarrassed.

While Garai says she's political, she also says she doesn't want to use her profile for political purposes. Yet, for all her chattiness, it's easy to imagine an older Garai writing fiercely political films or else taking on Susan Sarandon's actor-activist mantle.

But while conscious of the importance of Churchill's muscular response to Nazism, she feels differently about the Iraq war, not least because she saw some of its effects when she visited refugee camps on the Syrian border last year. Yet you sense part of her stated reluctance to mount a political soapbox too readily is because she has seen too many actors reveal a degree of unworldliness by immersing themselves in subjects they have not mastered or to which they lack an enduring commitment.

She cites the British anti-Iraq war demo: "It was so self-satisfied. We thought we'd walk around London one Saturday afternoon and then we wouldn't go to war. It wasn't until Obama and the US election that I saw my American friends, the actors I know, who didn't just go on one protest. They were cold-calling people, they really engaged with it. In retrospect, we didn't do enough." On Afghanistan, though, she's not tempted to express a view.

Born in Hong Kong in 1982, Garai spent the first six years of her life in the former colony and in Singapore until the family moved back to England and settled in Wiltshire. (Her great-grandfather, Bert Garai, had moved to London in 1924 and founded the Keystone Press Agency.) She has not "yet" been to Hungary and feels modern, cosmopolitan and British. Her mother, Janet, was a journalist before marrying her banker father and having children. Garai started an English degree at the age of 18 and planned to follow in her mother's footsteps. But term began not long after she landed her first professional acting role, playing the younger version of Judi Dench's character in ITV's The Last of the Blonde Bombshells. As the offers came in, she quit studying to act full time.

Two other top directors with whom she has worked are Joe Wright, in Atonement, and François Ozon, in Angel. The latter did much to establish her as one of Britain's fastest-rising stars. She remains very close to them, and to Poliakoff, calling on them for career advice even now.

But despite the success, the academic itch remained. She went back to university part time and has just finished her English literature degree at Queen Mary, University of London. She raves about Britain's great 19th-century female writers, but can take or leave their 20th-century male counterparts. She doesn't call herself a feminist, but gender is clearly very important to her – and to Poliakoff. "He writes amazing parts for women," she says, "and this [her role in Glorious 39] was an amazing role for a young woman."

Slim, tall, very pretty and stylishly turned out in a Margaret Howell silk tea dress, grey cardigan and men's brown brogues, she looks very much the edgy rising star. But, though she is excellent company and we spend much of the interview laughing, Garai is no party animal. She prefers her book club – held at her west London flat every month with an assortment of school and actor friends – to celebrity hangouts where she can't get a seat on a Friday night.

She devours as many films, plays, TV shows and musicals as she can. Fish Tank is her favourite film of the year; she loves Mad Men and has seen Jersey Boys twice. And unusually for an artist so young, she laments the decline of professional criticism in the arts. Books, films and plays that divide critical opinion are the ones that appeal to her most.

Like many in her profession, she has spent a good deal of this year "resting", but for her it is by choice. While acting is what she wants to do for now, she nonetheless hankers after writing, for which, she says, she needs to spend time in London. "I need to interact with the city," she says, "to meet people, to have strange things happen to me – otherwise what would I write about?" She writes more and more as she gets older, feels that she's improving and may end up doing the Open University's creative writing MA when she can afford to take a year off.

But she struggles with the loneliness of writing and always misses the interaction and collaboration involved in acting. "I like people, I'm social. So I find that part really hard. I'd actually really love to review books and films and plays, but you can't be an artist and a critic. I would love it if I could."

Garai is the second youngest of four children: Ralph and Rosie were adopted as babies before she and sister Roxy were born. She has a two-year-old bruiser of a nephew whom she adores. She tries to disapprove of his unshakeable love of trucks, cranes and all things boyish, but clearly loves the role of aunt. There is no Facebook, no blogging and definitely no Twitter in her life, just the old-fashioned phone to keep family and friends close.

This is a young actor who takes her job very, very seriously but – give or take the odd lapse into arts-speak – as yet lacks the self-importance that artistic success can bring. "When you start out, you get whipped into a frenzy of self-analysis, which can make you quite neurotic. But I've been very lucky in my career, I've made films with great directors.

"To be the tool of great, visionary auteurs like Stephen and François, well it's been a dream. But I've also taken time out to do theatre. I live in London, I'm very close to my family, and most of my friends don't work in the industry. So at the end of this 10-year process, I can now say I am able take it as it comes. I love my job. It's more than a job to me, it has a moral purpose, but I'm definitely not lying awake at night worrying about it."

Next year will be all about theatre for Garai, but she won't reveal what productions are in the pipeline. And after that? Well, there are one or two more "auteurs" she would love the chance to work for: Mike Leigh and the Coen Brothers are high on her wish list. (A girl's got to have a dream, after all.) Musical theatre is also on that list, but a guest appearance on The Simpsons with the feminist icon Lisa – well, that really would cap it all.

Curriculum vitae: A decade dedicated to her art

1982 Born 6 August in Hong Kong, where her father was a banker

1998 Leaves the family home in Wiltshire to live in London with her older sister and study at the City of London School for Girls. Joins the National Youth Theatre

2000 Appears in Last of the Blonde Bombshells after being spotted by an agent while still at school.

Role in the BBC series Attachments

2002 Wins first major film role in Nicholas Nickleby

2007 Stars as Angel Deverell in François Ozon's Angel, which earned her a nomination for the Prix Lumiere award, the French equivalent of the Golden Globes, as Best Female Newcomer – the first British actress to be nominated for the award.

2007 Stars alongside Keira Knightley and James McAvoy in the Oscar-winning Atonement

2008 Appears in two Royal Shakespeare Company productions, as Cordelia in King Lear and Nina in The Seagull

2009 Stars in BBC's Emma. Leading role in Stephen Poliakoff's Glorious 39

'Glorious 39' opens in London this Friday and 27 November nationwide