For someone who has played some of television's more extreme manifestations of womanhood - most memorably, the indefatigable social climber Becky Sharp in Andrew Davies' 1998 adaptation of Vanity Fair and the passive-aggressive schemer Rachel in This Life - Natasha Little comes across as dramatically, surprisingly normal.
Previous interviewers, it seems, have mistaken her rather unremarkable air for "mystery". "I don't know where that comes from. It's not like I've sat there" - she gives a throaty laugh - "in my sunglasses, smoking French cigarettes and muttering." Far from it - today Little bustles into the Islington Hilton, strawberry-blonde hair awry, dressed in the colourful and slightly mismatched ensemble of a bright pink mac, flowery shirt, black trousers and trainers (she whipped off her big, plasticky tortoiseshell sunglasses as she walked in), and before she sits down, she's chattering about her visit to Chelsea Flower Show the day before.
"I've just got into gardening, so it was perfect. I was mad keen to see the alliums which are these flowers I haven't planted yet in my garden. I know it sounds ridiculous, but I haven't quite got over the miracle that you plant things and they do sprout up."
Little has spent the past two years tending to her life outside acting - quietly marrying the actor Bohdan Poraj and giving birth to a son, Gabriel - and is now preparing to return to centre stage, in A Voyage Round My Father, at the Donmar Warehouse. "I love acting. It's what I do, not what I am," she tells me firmly, and it's true that she is a thoroughly un-actorly interviewee, censoring herself at the merest hint of luvvieness. Even her seemingly innocuous comment "I love rehearsing, it's the best part of the job" is followed by a wrinkled nose and a bout of self-deprecation. "That sounds like I've just graduated from Sylvia Young. Just draw a line through that," she grumbles.
She's more comfortable talking about the latest addition to her repertoire of strong female roles. In John Mortimer's autobiographical play, Little stars as Elizabeth, the outspoken divorcée who marries into the clan. Her husband (Mortimer's character) is played by Dominic Rowan, while Derek Jacobi and Joanna David are the venerable in-laws. The affectionate "voyage" touches on pivotal moments in the writer's relationship with his father, a gruff barrister who is at his happiest when tending his beloved dahlias, and who refuses to acknowledge (or allow his family to acknowledge) his blindness.
Elizabeth, arguably the only female role with any colour in Mortimer's exploration of filial love, explodes into this genteel set-up ("She has nice eyes. Not at all the eyes... of a divorced person" is the mother's rather weak first impression). "Elizabeth sees the son's father and his family with outside eyes. She opens his eyes to the oddity that they never talk about his father being blind," says Little. "I don't think she's harsh, I think she's really direct. The father appreciates the fact that she answers back; John described her as 'a bit spunky'."
Not only must Little and the cast contend with the ghosts of previous productions, including the Haymarket original in 1971, with Alec Guinness as the paterfamilias, and the much-loved 1982 television adaptation, which paired Laurence Olivier and Alan Bates as father and son, with Jane Asher as Elizabeth, but they also face the challenge of capturing real people - in Little's case, Mortimer's first wife, Penelope Fletcher - under the eye of the man who knew them better than most.
"It's such a privilege to have John Mortimer in rehearsals. Not only do you have the playwright, but you've also got the man, the character," says Little. "What's quite difficult is not getting stuck in thinking: 'I'm playing Penelope Mortimer.' I'm playing Elizabeth in the play. I see pictures and I think: 'Oh god, I must have a dark wig, I must try to capture that patrician beauty.' It's a tricky line."
The director, Thea Sharrock, has taken a simple approach to the episodic, chronologically mixed-up drama. "She has tried to strip down everything that we don't need, which as an actor can leave you feeling very exposed," says Little, whose last foray on to the stage was three years ago in The Vagina Monologues. "That was... a real challenge. The director, Irina Brown, asked me and I said: 'Ooh no, I don't think it's my cup of tea. I can't even say that word.' She said: 'What's your problem? Why can't you say vagina?'" Little breaks off giggling and shamefaced. "I can't even say it now without laughing. I thought, maybe it would be good for me" - she rolls her eyes, hearing the dreaded actor's voice again - "to do something that's beyond my comfort zone." It was not so much the X-rated subject matter as the personal touch the piece demanded that troubled the fiercely private Little. "You're playing characters, but for part of it you're playing yourself," she flaps her napkin around and looks uncomfortable. "That's something I've never done before and I don't think I'd want to do very much again. As an actor you've got the security of a character and that's nice."
Apart from a cameo as an actress in a period drama, opposite Ross Kemp, in Ricky Gervais's Extras, A Voyage Round My Father is Little's first main role since she gave birth 18 months ago. "My little boy is just a joy. I'm really glad that I've gone back to work now, because a big part of me would have been quite happy to stay at home for ever." Surely the prospect of making her "comeback" on stage is a little daunting? "I always find calmness in the fact that we're just telling a story. What's the worst thing that can happen?"
This no-nonsense approach perhaps stems from her relatively late introduction to the profession. Born in Liverpool in 1970, she spent much of her childhood travelling around the Middle East ("by the time I was 10, I had lived in 11 different countries") with her father, who worked for the World Health Organisation, and her mother, an English language teacher. "I thought that to go to drama school, you had to be the son or daughter of an actor. I didn't look much beyond what the other people in my family did. It was off my radar." It was only after a nudge from a teacher at her sixth-form college that she decided to apply to drama school and, even then, having gained a place at the Guildhall, she didn't start to think seriously about an acting career until the third year ("I was too immersed in having a great time").
She has barely been out of work since graduating, owing her break into the big time to the zeitgeisty lawyer soap This Life. The climactic moment of the second series, in which Milly punched Little's snitching Rachel, was voted the 37th most memorable scene ever shown on British television in a Channel 4 poll. Sweetly, Little doesn't really know why her character aroused such antipathy. ("Everyone said Rachel was terrible and manipulative. I just thought she was a bit slow and insensitive.") Vanity Fair followed, bringing Bafta and Royal Television Society nominations for Little's cheeky, gutsy performance as a snub-nosed, flame-haired manipulator of the social order. "I loved Becky - she's the most amazing woman. Am I like her? I wish!" she throws back her head and laughs. "I suppose in everyone there's a little bit of the devil, isn't there? It's just bringing that to the surface." Since then she has clocked up regular big television roles, including Man and Boy and Spooks.
The film CV is a little patchier: there have been minor Brit flicks (The Clandestine Marriage, The Criminal, Kevin & Perry Go Large) but Little's experience of Hollywood so far has been largely frustrating. In the hype generated by Vanity Fair, she was offered the lead in Enigma opposite Dougray Scott, but the part was taken away from her when Kate Winslet became available. Little walked away with her full fee (£300,000), taking instead a part in Richard Eyre's production of The Novice at the Almeida. Then, in 2004, came Mira Nair's Indian-flavoured Vanity Fair, in which Reese Witherspoon became Becky, while Little was cast in the minor role of Lady Jane Sheepshanks. Apparently, there was only one "bizarre" moment, when Little found herself in the "same location, different frock, different character" but, she says archly: "I didn't feel the need to rip off Reese's wig and shout: 'I am Becky Sharp!'"
She is now understandably cagey about future films, although she lets slip that she is to star in an American comedy, The Day I Ran into All My Ex-Boyfriends, and has been asked to do another film, The Darkest Place ("You know these things, they might turn round next week and say that they want somebody else"). She has no burning desire to "crack" Hollywood, and you sense that she feels there is more to life than chasing parts. There is a lovely moment when I ask her whether she knows anything about a rumoured 10-year This Life reunion. "I haven't heard. I hope if it happens, they invite me," she replies, looking a little hurt. I waffle on about the difficulty of revisiting Rachel after a decade. She stops me, relieved: "Ohhh, do you mean a reunion programme? I thought you were just talking about a booze-up!"
As for being forever ensconced in the popular imagination as a scheming minx in a bonnet, Little doesn't see it as a problem. "I don't worry too much about being typecast," she says, her pale blue eyes sparkling, her chin raised in Sharp-esque defiance. "If you're at the stage where you think: 'I'm getting fed up with playing these famous, dynamic, fantastic women', something else will come along, hopefully."
'A Voyage Round My Father', Donmar Warehouse, London WC2 (0870 060 6624) today to 5 August