A KNOCK at the door. Kelly Reilly takes receipt of another bag, emblazoned with the name of skincare company Elemis. She dumps it guiltily in the corner of the room. A couple of frocks have already been ferried upstairs this afternoon by hotel porters and publicity assistants. She's embarrassed by the fuss.
She would much rather be watching the Inspector Clouseau film that's on telly, settling down with some tea and biscuits. Her pale-fire hair is tied up but bursting out in straggles. Her white, freckled face is as-yet untouched by lippy, mascara or blusher. She huddles into her woolly jumper.
Soon she will be driven in a fancy car the few hundred yards from her Soho hotel to her Leicester Square premire. She'll be running the paparazzi gauntlet later today and shudders at the prospect. She's the A-list actress and cover-star who has no interest in being either. Back home in Surrey, policeman dad and hospital receptionist mum would be proud.
So, by way of an icebreaker, and taking my cue from Reilly's costume in the new Sherlock Holmes film, I'm telling her about Keira Knightley's underwear. During the filming of one of the Pirates of the Caribbean films, her corset was strapped so tight she fainted in the sunshine. And even at the best of times the physical restriction meant that, with her acting, "everything slightly changes", Knightley told me. "The way you sit and the way you walk change. And also, if you're out of breath, your emotions are much higher."
"I completely agree with her," says Reilly, who starred with Knightley in Pride And Prejudice and who is like an edgy, credible version of Hollywood's favourite young British actress. The Dark Knightley, if you like. "When you first put on a corset it's like someone just sucked all the air out of your body and you're talking like that," she grins, adopting a squeaky, high-pitched voice. "You feel you can't sit down, you can't walk, and God forbid you'd want to eat anything."
A corset was required for her portrayal of Desdemona in the acclaimed London Donmar Warehouse production of Othello two years ago, in which she appeared alongside Ewan McGregor and Chiwetel Ejiofor. "And because that was on stage, night after night, you really need to be able to have your lungs expand. And I found the corset, that tension, was really good. You used it for the role."
She even rehearsed trussed up to the gills. "I had to get used to it. Luckily, I've worn enough corsets to know that I needed a little bit of time in it. Because it starts to mould around your body. It starts to become part of you."
Self-deprecating, self-lacerating and guilty: you don't get many successful young actors like Reilly. Her screen performances may suggest another English semi-posh actress who looks good in bonnet and corset. But there's a depth to her, and a darkness, that sets her apart. There's a relaxed confidence too – a quality that makes her great company (she would seemingly quite merrily chat all afternoon, batting away the PR's overprotective overtures) and cool enough to not cravenly court publicity.
"This job has definitely toughened me up. I remember doing a play called Piano Forte at (London's] Royal Court about three years ago, and I'd just come out of a really terrible break-up. And I was feeling really fragile. And this character I was about to play was not fragile. She was the strongest character I've ever played. Well, ultimately she ended up killing herself. But put that small detail aside – I vowed not to do any more suicides, ha ha! – the fact that she was completely powerful and strong and in the swing of her life, that kind of thing can really help out in your private life. You can borrow things from characters. Because you go to a different place in your head that's not you. And it can invigorate – as well as being difficult."
And so to Reilly's current big-screen role. She's Mary Morstan, other half of Dr Watson, in Sherlock Holmes, Guy Ritchie's testosteroned adaptation of Sir Arthur Conan Doyle's legendary detective tales. Because this is a movie by Ritchie – he of Lock, Stock and Two Smoking Barrels and other very loud films – it's out with the deerstalker and in with the martial-arts machismo.
"Reinvigorating," is how Reilly describes the Ritchie approach to the classic detective yarns. "It's not about harking back to what was necessarily in the books. It's taking it from a modern filmmaker's interpretation and just having fun with it."
And because this is a Ritchie movie, there's lots of buddy-buddy tomfoolery between Holmes (Robert Downey Jr) and Watson (Jude Law), and not so much room for the ladies. So sidelined are the female roles (American actress Rachel McAdams stars as Holmes's love interest) that Reilly won't even be getting any Best Supporting Actress nominations. But she might get a Best Supporting Dress nod as Mary bustles about in swishy Victorian finery.
"Mary is one of those women who wishes she could have a job. I can't imagine what it must have been like in those days, when you just had to wait for the husband to come home. Fine if you had children. But if you didn't," says Reilly, eyebrows shooting skywards, "you'd get bored out of your mind."
Reilly is not one for fragrant platitudes. Nor does the Home Counties-born 32-year-old go in for coy puffery of the type so often beloved of young actors. She would hate me to think she has a big role in Sherlock Holmes. Getting the part was not something she worked hard for. "I was very lucky that it was offered to me. I didn't have to audition for it." It was more about having the chance to work with Downey Jr than it was about appearing in a big-budget film that would get loads of press.
And as she orders us room service, she admits she was mortified when her PR had earlier tried to cut short our allotted interview time, seemingly because of tonight's West End premire (for her other recent film, Me And Orson Welles). "Yeah, there's the premire later, but beforehand all I'm doing is sitting around in the hotel." And, ultimately, her short time on the Sherlock Holmes set was considerably less fulfilling than her new small-screen role, playing Detective Constable Anne Travis in ITV's Above Suspicion.
The three-part detective drama is adapted from a series of books by Lynda La Plante, creator of Prime Suspect. After healthy ratings for the first two-parter early last year, Travis is back in a new story, called The Red Dahlia. She's a member of a police squad pursuing a psychopathic copycat killer "inspired" by the unsolved Black Dahlia murders that occurred in Los Angeles in the 1940s.
"My first meeting with Kelly for the role of Anna Travis made me very excited," recalls La Plante. "She was the right age, a natural redhead, like the character, and her father is an ex-police officer – almost too good to be true. Often when auditioning actors, they appear to look exactly right but then you have to consider whether or not they also have the acting talent. Kelly ticked every box and her professionalism and dedication have exceeded all my expectations. She is a star."
Reilly is brilliant in the role, utterly believable as the young, smart, dogged policewoman whose father was a respected copper. There's no getting away from her attractiveness, but creditably it is never played up in Above Suspicion, with more focus given to her investigative mettle. She's a world away from La Plante's most famous character, Jane Tennison, as personified by Helen Mirren.
"Exactly!" exclaims Reilly, wary of being bracketed with Mirren's iconic performances. "It's boring to me, that comparison anyway. And why don't we just try and do something different? Let's not forget that actually Lynda La Plante has created a character that is completely different. Tennison was a character that was established in her career and was coming up against all these sexual politics, and it was about the first woman going up that far into the ranks. That's not what we're talking about. There's no sexual politics with Travis. It's about someone beginning their career, starting out as a very fiercely talented, instinctive police officer. She has to prove herself because she has actually got up the ranks maybe a little bit because her father was brilliant, so she has to prove her worth that way."
It wasn't just the difference of the character that appealed. It was also the brevity – a three-parter suits her fine. "If it was a big, long series I probably wouldn't be interested. I can get bored," she beams, "and I want to play the next character. Maybe cut to ten years' time and I might be happy to do that. But at the moment, no."
Instead, Reilly was drawn by the chance to "revisit" the character one year on, to track "how she has grown and where she goes next". So, in the same way that she used the restrictions of corsetry to play Desdemona, she used her interpretation of La Plante's books to imagine Anne Travis's professional and personal development.
"And my interpretation had to be that she felt she had every right to be there. She'd earned it. She'd proved herself. And now what other challenges are there? And how can you be the best at your job? And at a job that also requires you to put life on hold, because it's all-consuming. And this particular case that she investigates is really bleak."
Can we say the same of Reilly? That having worked with respected directors Stephen Frears (Mrs Henderson Presents), Joe Wright (Pride And Prejudice) and Stephen Poliakoff (Joe's Palace), as well as having earned plaudits for heavyweight theatrical work (Othello, Sarah Kane's Blasted), she has earned the right to be choosy, to be outspoken about the limitations of scripts and the futility of comparisons? "Yeah," she says with a smile, "why not? That has definitely been a colour running through (my career]. Mine being a much longer timespan, because I've been doing it since I was 17."
That debut role, ironically, was in an episode of Prime Suspect – Reilly, freshly moved to London to pursue a career in acting, won the bit part after persistently approaching the casting director. "And for a while every job felt like my first. Because I didn't go to drama school, I really was aware this wasn't a world I just easily fell into. It was something I had to keep working really hard in. I never felt my feet were under the table, so to speak. And it's not that I feel like that now," she adds quickly. "But I do feel the confidence of my CV. The experience is the thing that is interesting, and that's why people want to employ you. Not because you're on the cover of a magazine."
For Reilly, directors' interest in her "had to be real. It had to be worth it". Rafe Spall, actor son of Timothy, who starred with Reilly in 2007's TV drama He Kills Coppers, and in a London theatrical production of A Prayer For Owen Meany, echoes this. "Kelly doesn't do anything she doesn't believe in. She doesn't do anything just for money."
All of this has come, in ways good and bad, at some cost. On a personal level, Reilly admits that friendships have suffered for the sake of her work.
"Literally, I don't know where life is gonna go from one day to the next," she says, her posh/street voice rising and falling in mild exasperation, "and that's as exciting as it is tiring. When I'm back in England with my friends and family they're like, 'How long are you staying for?' And sometimes you can feel you're not very reliable. You're constantly going, 'Well, I'll call you when I land…' And I'm quite impulsive anyway. I'm trying to calm that down. But because I'm impulsive, the job tends to suit me – not knowing (where I'm going next], I find that quite exciting. But at the same time trying to find some stability…"
Not least, it seems, because professional commitments seem to have put something of the kybosh on her relationship with New York-based Israeli actor Jonah Lotan. She spent time with him in Namibia while he was filming Iraq War mini-series Generation Kill, and they were due to be married last year. But today she's wearing no ring and bashfully declines to say whether they're still an item, stammering that "it's complicated".
"This is why I understand a lot of the English actors who go off to LA to go do television series," she says, moving swiftly on. "Because a) they're gonna get a nice job that's gonna pay more money than they'd ever earn in England, and b) they know they're working for ten months of the year, then come home for two, and they have family with them, and it's the closest thing to a regular job. I think there must come a time when that's really appealing."
But not, seemingly, right now for the footloose Reilly.
"It's tough in UK at the moment. The work just seems to be for the very few…" Absolutely, she nods, she worries about her next job. "And I know I'm one of the lucky ones. Believe me, I know. Some of my best friends are actors and they're not working, and they really should be because they're really talented. And they're just not getting the breaks because it's the same group of people getting the work – and I am one of them," she laughs. "So when I moan and go, 'Oh, it's the same faces (starring in everything]', that's me!"
She mentions another key theatrical role, in the Donmar Warehouse's 2003/4 production of After Miss Julie, an adaptation of August Strindberg's Miss Julie by writer and actor Patrick Marber (Closer, Dealer's Choice) for which Reilly was universally acclaimed. "By the time that run finished, I thought I'd have to go into a little hole in the ground for a few months... And whether I like it or not, darkness is definitely something that I am drawn to, weirdly. I don't meant like goth stuff, like horror. I just mean more complicated, darker parts of the human psyche, of how we try and cope with things like grief and anything that could be difficult; anything that is a challenge. Whatever it is that is someone's demon on their shoulder, their bugbear. I'm usually more intrigued to find out what that's about, and how they can function and survive."
Reilly is, right now, available for work. "Nothing lined up," she says brightly. "It's a blank canvas. Which I like too." But she's reading scripts and hankering after something substantial. If, as rumours suggest, Sherlock Holmes 2 is in the pipeline, she would be interested – but only if the part "was a bit more involved". And she's ready, she thinks, for another play. She was worn out after Othello, and batted away suggestions that she might next take on heavyweight plays such as Henrik Ibsen's Hedda Gabbler or A Doll's House. The actress who used a corset to shape her body to shape her part "just couldn't think of anything worse after doing Desdemona".
"I'd like to do another comedy. Piano Forte – apart from the suicide – was very funny. And I really enjoyed that. So we'll see what happens next year. I haven't got a real plan yet. But another play would be great. I wouldn't be without the theatre. It's just such a nice place to go back to and regroup, and make sure you haven't gone fey with the film acting; to make sure you've still got a bit of muscle."
• Sherlock Holmes is in cinemas now.
• Above Suspicion: The Red Dahlia is on ITV, 4-6 January, at 9pm
A version of this article first appeared in Scotland on Sunday on December 27