Frankly, it is a surprise to find Jane Eyre talking mockney. You might expect a hint of Haworth in the occasional put-upon vowel sound, but not “Yeah, yeah, yeah, yeah, yeah”, “Innit?” and “Do you know what I mean?”, tinged with the salt-and-vinegar tang of the Thames estuary.

Ruth Wilson, the 25-year-old newcomer Bafta-nominated for her television interpretation of Charlotte Brontë’s governess, has come straight from rehearsals for her National Theatre debut as Tanya in Gorky’s Philistines. “I read the script and thought, ‘Oooh, she’s dodgy,’” she says, pulling a face, as she sets down her glass of red wine. “I mean, she’s a funny one. Have you read it?” I nod. “Yeah, it’s quite stodgy, innit? But off the page, it’s great. Phil Davis and Rory Kinnear have these huge speeches that just roll off the tongue.”

As much as anything, the accent jars because there is nothing in Wilson’s CV to suggest it should be anything other than RP. Brought up in Shepperton, she attended Surrey’s Notre Dame School for girls before sixth form at Esher College. Having secured straight As at A-level, she read history at Nottingham University, then her supportive parents funded her to pursue her dreams with a postgraduate acting course at Lamda.

The clue is in the short walk from the rehearsal room. Though less than two years out of drama school, Wilson has proved herself a chameleon who takes technique seriously. Last autumn, her Sunday-night BBC Jane Eyre earned plaudits and ratings. When the nights draw in again, she will be back, in one of Stephen Polia-koff’s lush BBC ensemble dramas. In Capturing Mary, Maggie Smith plays a journalist recalling a youthful encounter that changed her life irrevocably. Wilson, in flashbacks and red hair, plays the young Mary and, thus, the young Smith.

“I didn’t want to do an impersonation of Maggie, because that could drag away from the character I wanted to put my own stamp on,” she says. “So it was about the voice – not doing too much of a Maggie voice, but getting mine a bit higher and more RP.”

In Gorky’s bleak, black 1902 comedy, too, she has been experimenting with accent and vocal tone. Her character, Tanya, is a spinster schoolteacher, the daughter of a graspingly upwardly mobile artisan. “Phil Davis and Stephanie Jacob, who play the parents, are really estuary,” she says. “Rory and I speak as I am now because we’re better educated. It’s written brilliantly: voices cut over each other and sometimes just trail off, which is so true to life. But you can’t drop the ball.” This new English version is by the Australian Andrew Upton, probably best known here for being Cate Blanchett’s husband. He is, according to Wilson, “a complete legend”.

Wilson heard she was up against Anne-Marie Duff, Samantha Morton and Victoria Wood for the best-actress Bafta two days after rehearsals started. “The whole thing has been mad, but amazing,” she says of the nomination when we meet a fortnight before the awards ceremony. “I mean, I’ve been getting designer dresses sent to me. I think I might have this Alberta Ferretti thing in there,” she says, indicating a large parcel on the table between us.

Wearing another lent designer dress, she was the only one in her category to attend the nominees’ party, moving through a celebrity hotchpotch that included Alan Sugar, Life on Mars’s Philip Glenister and Simon Schama – in spats. Her father had once given her a Schama box set, so she approached him. The encounter, as she retells it, seems to have turned her into one of Catherine Tate’s rude schoolgirls. “I went up and said, ‘Hi, Simon, I think your work’s great.’ And he said to me and my boyfriend, ‘You must be a nominee too ... congratulations – what for?’ And I was like, ‘Yeah, for Jane Eyre.’ And he was like, ‘Oh, yeah, what did you do in that?’ And I was like, ‘Oh, I’m an actress and I played...’ And he was like, ‘Oh my God, it’s you.’ He’d totally seen it, but he didn’t recognise me.”

Wilson was too intimidated to mention her history degree to him. “I would feel hugely inadequate, like it would go in one ear, then out the other,” she says. “So I didn’t indulge in the history with him.”

Though enjoying the free clobber and her proud mother’s excitement at being taken to the Baftas, Wilson would prefer to keep the celebrity whirl at arm’s length. Her boyfriend is not an actor, but a web designer. Of her Capturing Mary co-star, Little Britain’s David Walliams, she says: “He’s such a lovely guy, but he lives a mad life. He went to Australia for a few weeks after we’d finished filming. Later, I was like, ‘I wonder when David’s back.’ So I flicked through a newspaper and there he was. I mean, if I were to run the marathon, I’d prefer not to be noticed doing it.”

She would prefer to go down the route followed by actresses such as Smith and Emily Watson, who craft characters; A-listers who avoid the circuit. Already, she has established in her own mind that she is drawn to playing outsiders. “I have been so blessed with my family and life, touch wood,” she says, rapping the table. “So I do find playing those who have suffered interesting.

“As a person, you always want to be loved. As an actor, you have to fight that instinct to be like, ‘Love this person.’ Take Tanya: she can be nasty, vindictive and annoying, but she is a desperate girl in a desperate situation. She needs help, but nobody’s listening. So I’m trying to be brutal and make her who she is, yet show the moments of weakness when the audience might empathise and sympathise with her.”

Though briefly a teenage model, Wilson has a duckish mouth and vivid colouring that make her arresting rather than stereotypically pretty. She can look beautiful, but she is not drawn to those roles. “For me, there is a stigma attached to playing beautiful parts. They are often empty characters whom the action happens around. I’m more drawn to characters with a complex internal life, who have a burning frustration underneath that keeps them going. I wonder if that is because I have that.”

She is anchored in her career by parents so supportive, they have already booked into at least five performances of Philistines – including the first preview.

“I said, ‘Mu-um, that is my first time on the National stage. I’ll be bricking it anyway, and Philistines opens at the Lyttelton, National Theatre, SE1, on Wednesday; Capturing Mary is on the BBC in the autumn you’ll have all these people, probably sitting in the front row, going, c’mon, Ruth,’” she says, giving herself a thumbs up. “But they will be very supportive, whatever,” she adds hastily, for fear of sounding churlish.

Tempering the unstinting endorsement of her parents are three elder brothers who can be stingingly honest, and with whom she has always been intensely competitive. “I hate it, but my competitiveness is very deep-rooted,” she admits, laughing. “It’s lucky I’m doing all right, because if it was the other way round, I’d be horrible.”

“All right” barely does justice to her career so far, which she describes embarrassedly as “amazing, but a bit mad”, before admitting that she is only just getting used to working. “You know, you go from school to uni to drama school, and everything is timetabled sensibly. But with acting, you are either really solidly working or off, and a little bit frightened by what might be next. So I’m still getting used to that. Yeah, I’m still getting used to being an actress.” She pauses, then corrects herself, not that convincingly: “Or an actor.”

She did not win the Bafta last Sunday. It went to Wood for Housewife, 49. Accepting the prize, Wood pointed out that her fellow nominees were all much younger, and had years yet to win their own gong. The camera panned round to the youngest nominee, Wilson, looking pretty in an electric-blue – presumably Ferretti – dress. She was clearly doing her best not to look, in her own phrase, gutted, but the best she could muster was a wistful smile.

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