For a British actress, tying the ribbons on a period drama bonnet for the first time is an important rite of passage. For Claire Foy, though, the occasion was particularly memorable. In 2008, aged just 24, she landed the lead role in Andrew Davies' 14-part adaptation of Little Dorrit, having previously appeared only in the pilot of Being Human and in a single episode of Doctors. All of a sudden, she was being directed by her teen idol. "I've seen Pride and Prejudice about 4,000 times. I'm not joking: I know every single line. I used to go round to my Aunty Cath's house and we'd all sit under the duvet and spend all day watching the whole thing. I was obsessed," she says. "So when I first saw my bonnet, I was like, 'Are you kidding me?'"
Today, Foy still can't quite believe her luck. She is endearingly wide-eyed about her chosen profession, even though, at 27, she has a CV to rival actors twice her age. Before she has even sat down, she's gossiping about the time she auditioned for Ben Stiller. "I went in and thought, 'Oh my god you're Ben Stiller!' It was just the worst audition ever. Needless to say I didn't get it."
She flops down on the sofa and unwinds her long woolly scarf. "But it was so nice to meet him." She is starry-eyed about Hollywood in general, though she already has one blockbuster – Season of the Witch – under her belt. "They closed a ski lodge for us all to stay in on the shoot! Only because we were with Nicolas Cage – they wouldn't have closed a ski lodge for me. I haven't been to one since." She's now planning to go to LA next year, in pursuit of more film roles. "It's so warm! And it smells amazing! It smells of oranges and sunshine and attractive people!"
You can see Hollywood falling for this British ingenue in a big way. She has the kind of delicate English rose features and gigantic blue eyes that make directors swoon. (Davies said that he wanted every shot in Little Dorrit to be "a big close-up of Claire and those huge eyes and that wonderful straight gaze..."). Yet when she opens her mouth, she's surprisingly loud, an unstoppable chatterbox, all estuary over-emphasis and ohmigods.
It's a combination that has made her hard to typecast so far. She followed up her angelic Amy Dorrit with roles in two further classy television adaptations – of Sarah Waters' The Night Watch and Terry Pratchett's Going Postal – and the lead in Peter Kosminsky's Israeli independence drama, The Promise. Lately, she's taken a turn for the villainous, playing a plague-spreading sorceress in Season of the Witch and the brattish, fascist-supporting Lady Persie in Upstairs Downstairs. This weekend, as if to confirm her passage to the dark side, she plays the editor of a tabloid newspaper in Hacks, a one-off phone-hacking comedy on Channel 4. "I've played quite a lot of horrible people recently," she says. "I probably need to stop that."
Written by Guy Jenkin (Outnumbered, Drop the Dead Donkey), Hacks stars Foy as Kate Loy, "a ferociously ambitious newswoman who believes that you should do anything to get a story". Loy is appointed to the top job by the newspaper's Australian owner (over the head of his impotent, bespectacled son), celebrates by spending the night with a well-known soap star and when, on her first day at the helm, she's presented with a pile of files by a journalist, demands, "Why won't you just hack phones like everyone else?" She's also, according to Foy, "completely fictional" and wears her dark brown hair in a severe bob rather than, say, wild, red curls. Still, Foy must have looked to recent events for a little inspiration? "No, I deliberately didn't. It's not based on fact, it's a comedy drama. It's close to the bone but that's what comedy is."
Has she experienced any press intrusion? "Not really. I'd be really shocked if that happened." In fact, fame is a strange source of fascination for her. "It must be weird if you're a proper star and you just go from amazing place to amazing place, never going anywhere horrible, never having anything slightly cruddy, never having unwashed clothes," she says, eyes like saucers. "But that's life. You need stuff like that."
She went to the Baftas last year but left straight after dinner. "I was eating guinea fowl at midnight thinking, 'This is really weird. I'm not hungry anymore. I'm really tired. Shall we just go home?' I watch the Baftas every year and I love it. It's so glamorous and exciting, then when you actually go... I'd rather watch it at home, if you know what I mean." Home is Notting Hill – "Swit swoo! I'm very lucky" – where she lives with her partner. She has previously kept his identity a secret but tells me that it's the actor Stephen Campbell Moore. They met on the set of Season of the Witch.
Foy has just starred in the British indie movie Wreckers, playing Benedict Cumberbatch's wife. "Filmed on a budget of 2.5p," she says, cheerfully. "Benedict has a huge female following. They'll probably come after me now. Start going through my bins..."
Foy never planned to be in front of the camera. Born in Cheshire, she moved to Buckinghamshire when she was six, after her parents divorced. The youngest – and loudest – of three children, her performing career got off to a stuttering start when she fell off the stage while playing Titania in a purple tutu at primary school, and she later had to give up ballet thanks to juvenile arthritis.
She did drama and screen studies at Liverpool John Moores University and toyed with becoming a cinematographer – "until I realised that I didn't understand what the lights did". It was only a chance remark from one of her lecturers, about acting, that set her on a different path.
"I was a bit confused. I loved film so much but it didn't occur to me to be an actress or go to drama school." She applied to Lamda but didn't get in and instead enrolled on a one-year course at the Oxford School of Drama. A year later, she was tying her bonnet on the set of Little Dorrit.
She's now filming another period drama – the second series of Upstairs Downstairs. Foy plays Lady Persie, the petulant sister of the lady of the house (played by Keeley Hawes; the two look spookily similar), who becomes embroiled first with the family chauffeur, and then with fascism. "I get to play a complete loony," says Foy, with relish. "People hate her but I think she's amazing. I love her. I'd quite like to be her friend – discounting the fascist bit, obviously. There's no excusing being a fascist, but if I've got to play her, I can't say 'I'm not going to do that because people won't like her.'"
'Hacks' is on on 1 January at 10pm on Channel 4 ; 'Upstairs Downstairs' returns to the BBC early next year