Watch this face: Vanessa Kirby on Kate Mosse's Labyrinth, Richard Curtis and a stint at the National

BBC adaptation of Great Expectations, playing Estella to Gillian Anderson's Miss Havisham. Doing a telly Dickens is almost a rite-of- passage for young British actresses, but – despite a newspaper article claiming she was part of 'the corset crew', a social coterie of posh, pretty young things who apparently hopped between costume drama sets and (it implied) each other's beds – Kirby has avoided being stuck in bonnet land.

She appears tonight – admittedly alongside chum Jessica Brown Findlay, who is indeed best known for Downton Abbey – in a lavish two-part TV adaptation of Kate Mosse's internationally bestselling novel, Labyrinth. And she's the love interest in gritty but heart-warming British indie movie, The Rise, while later this year, she'll crop up in Richard Curtis's rom-com, About Time, playing Rachel McAdams's brash best friend. But Kirby is also about to play a crack addict in the directorial debut of Andrew Hulme (editor of slick screen hits Control, and The American) and has, the day before we meet, been cast as Queen Isabella in a production of Marlowe's Edward II at the National Theatre.

She is, throughout our interview, vehement that it is this – the work, as varied as possible and as much as possible – that matters to her, not the trappings of fame, fortune or fashion. Of that corset crew clique, she is completely dismissive: "Oh, GOD. It was really weird because most of us don't know each other! It was just silly". Apart from when shooting Labyrinth, she has never – as was widely reported – lived with Brown Findlay. And Kirby remains tight-lipped, albeit sweetly apologetically so, on the subject of whether she was, or is, dating the impossibly pretty Douglas Booth, her plumply-pouting Great Expectations co-star.

"I don't feel like my job is to parade around saying what I'm wearing or who I'm going out with. It makes me feel weird," she says, early on. Later, gently pressed on whether her and Booth are an item, she adds, "I don't talk about my personal life. If it becomes about anything other than the work, people stop caring about whether you can do the job or not."

But it would be almost impossible to be cross with Kirby. She's impressively earnest about her work for someone who also brims and babbles with such enthusiasm. Infectious isn't the word – there's no cynicism strong enough to provide a vaccine against it. By the end of the interview she's all shoulder squeezes and nicknames (hers, she tells me, is 'Noo', while I have, quite uninvited, become 'Hols'), but it's in a chummy, all-girls-together way, rather than with any hint of manipulation.

Kirby certainly seems to be a girl's girl – despite being so ridiculously beautiful you'd expect to hate her, all long blonde hair, huge blue cats-eyes and endless limbs. She shares a house with three female friends, who work in theatre and fashion but are, she insists "normals" and like "sisters". When she arrives, Kirby's breathlessly talking about the cake she has to pick up for one of their birthdays, and the kittens they've just bought (she got points on her licence – "Naughty!" – while driving round endlessly to find ones with the "right personality") and you can just imagine curling up on the sofa with Kirby and the cats and nattering on for hours.

This girlish intimacy spills over into her performances. The Acid Test, written when its author, Royal Court wunderkind Anya Reiss, was only 18, is about a trio of girls in their twenties, unsure of what they're doing with their lives (aside from getting determinedly drunk). It was hilarious, and very recognisable, like a British theatrical precursor to Girls: "It was so exciting to work with actresses all of the same age group. It's really unusual to get that. Every girl [in the audience], no matter what age, said 'Oh my God, that's so us'." Her sozzled, now-sexy, now-sobby performance impressed the critics; The Independent's own Paul Taylor notably called her "a star if ever I saw one".

In Curtis's new movie About Time, she's playing another BFF, this time to leading lady Rachel McAdams. She replaced Zooey Deschanel – a move I can't help noticing Kirby seems a bit relieved about – and Kirby is full of wildly effusive praise: "We had the best summer doing it. She literally radiates".

Being part of a Curtis movie is surely another boxed ticked on the English Rose to-do list, and Kirby is characteristically delighted by the whole thing. "Richard's like family to me now… I felt lucky to be part of the team, on what might be his last movie, having grown up watching Notting Hill, and Love, Actually…"

She goes gooey when she talks about working with Brown Findlay in Labyrinth, too. Although they didn't have scenes together – the drama is set half in 2005, and half in 1209 – it's another project where female characters take centre stage, as both heroines and as ratherf crudely cartoonish baddies, with a minor male love interest or two on the side. "Kate [Mosse] and her publisher met all the Hollywood studios – it's been a bestseller in 60 countries, sold millions, so it has a big market, whoever's in it. But every studio said, 'OK, but who should we have as the guy?' Isn't that so ridiculous?" Which was why they went with Ridley Scott's production company, Scott Free, and opted for a TV series.

Two strong females remain at the heart of the story (albeit a story a little confusingly condensed from Mosse's epic, pacy, 700-page novel into two 90-minute episodes). They're played by Kirby and Brown Findlay – who got on like a medieval castle on fire, to judge by Kirby's account. "I'm like 'Jess, you're sooo gorgeous, you're such a knock-out!' I feel like the scrawny blonde on the side…"

Well, hardly. Even bundled up in a giant knitted jumper, it's hard not to notice Kirby's knock-out status, too. But she insists it isn't important to her. "I am learning not to give a shit about what you look like. Watching myself on screen the first time – Jee-sus. Now, I'd much rather not worry about [how I look], not play the Transformers role, the hotty in the hot-pants." Of course, it's easier not to care when you are rather stunning, and I point out that, with all respect, she could be the hotty in the hot-pants. This prompts embarrassed hand-waving: "That's so nice of you! Well – you haven't seen my arse, I haven't been to the gym in literally a year. But it's quite nice to release that."

It also spurs her to not let roles be just about being the pretty blonde. In The Rise – Rowan Athale's feature film debut, formerly known as Wasteland, and finally about to be released in the UK after promising film festival responses last year – she plays Nicole, a dolled-up Northern lass, who could easily be seen as the token bird in a lads' movie. "I didn't want her to be a blonde bimbo, on the side, trailing about whinging. I wanted her to be cool and likeable," she insists. Job done, I'd say – and her warm performance does indeed stop it being too narrowly blokeish. "It's not just a 'lads' film'; all my girlfriends that have seen it and loved it, my parents loved it."

It's really a movie about friendship, despite centring on four young guys on an estate in Leeds who plan a heist; the cast reads like a Young British Talent list, headed up by Luke Treadaway (Attack the Block, currently in the stage version of A Curious Incident of the Dog in the Night-Time), with Iwan Rheon (Simon in Misfits), Gerard Kearns (Ian in Shameless) and Matthew Lewis (Neville in Harry Potter).

It looks like it must have been a blast to work on, I suggest. "So fun. You can totally tell, right? I have really set my heart on making a lot of cool, independent films like that. It was low-budget but there was a good feeling about it."

You sense Kirby is one of those people who've been dealt a very good hand in life, but who genuinely wants to use it as best they can. She grew up in Wimbledon, her mum a founder of Country Living magazine when "it was quite feminist and different", her dad a surgeon, although, she jokes, "he secretly wants to be an actor I reckon – he always bangs on about playing Mark Antony at school". Her parents are very supportive, but very honest; watching audition tapes, her mum will say "I think you're mumbling, darling…" – but she also came to watch Kirby in Three Sisters "about 17 times. It got embarrassing!".

It was an artistic household: she was taken to the theatre often, and she, her older brother and younger sister, all studied English at university; Kirby netted a first, from Exeter. But she had long had it in mind that she wanted to be an actress. She was in the local am-dram group in Wimbledon, and played Gertrude in a school production of Hamlet ("I re-watched the video recently – and I was terrible"). Although Kirby went to "a lovely school, all girls", she confesses that she didn't particularly have a good time there. She applied to drama school, but at just 17, was told she was too young and to come back in a year.

Although, Kirby now acknowledges, that was absolutely sound advice, she didn't re-apply. Following a gap year, taking conflict resolution courses and working in hospices in Cape Town, and travelling around Africa and Asia, she decided to get an academic degree. "I am so glad I did it that way round, and hopefully in the long run it will make me a better actress, because it made me grow up, and learn what other people are like," she says.

Post-uni, a place at Lamda drama school beckoned – but so did an actual, real-life theatre. She'd met director David Thacker, who offered her a whole season of classic plays at the Octagon Theatre Bolton. "I had my heart set on [drama school]. I had to make a really hard decision, [but] I just thought, 'Fuck it, if I'm going to be doing Miller, Shakespeare, Ibsen…'." Now, she sees that 18-month repertory contract as something to be proud of, a grounding beginning to a career.

It was also a baptism of fire, learning on the job, and she confesses she "spent so long being scared". Within a year of graduating, Kirby found herself on stage at the National Theatre, with a lead role in Thomas Middleton's Jacobean tragedy, Women Beware Women, opposite Dame Harriet Walter. "I came out [of the audition] totally depressed. I thought, that's the worst thing I've ever done. I was on the train home, crying… My agent rang and was, like 'Well, I think you're going to be at the National for the next two months' and I literally went ballistic."

It was terrifying, though – she had to sing and dance onstage, and was suddenly very aware that she hadn't had those three years of jazz hands-ing at drama school. Not to mention "having to do these really difficult Middleton soliloquies to 1,300 people when I'd only just started working… I was just shitting myself, every single night."

She's calmer now, and looking forward to returning to the powerhouse venue. Not, she says, that the doubts ever fully go away. Filming Labyrinth with acting veteran John Hurt, she noticed he was nervy before shooting a scene. She asked if he was OK. "He was like, 'Yes, well, I'm just a bit worried I'm going to be found out…'. And I was like…" – here she explodes in a self-mocking burst of horror – "'You're worried, John? In that case, I'm fucked!'."

Despite this, somewhere, in the back of her head, Kirby always knew this was what she was meant to be doing. "I remember so clearly standing on the stairs at the National with my dad and saying – 'Dad, look at me, look at me. I'm going to be [acting] here one day'. And he was like 'Yes, yes, all right'. And then that was my second job! It was the most surreal thing. I just couldn't believe it. I'm only just getting my head round it now – that no one's going to take it all away."

'Labyrinth' is on Channel 4 tonight and tomorrow; 'About Time' is released in September; 'Edward II' is at the National Theatre, London SE1, in September; 'The Rise' will be released later this year