Strange case of the cameo killer: Why is Kelly Reilly playing second fiddle in Sherlock Holmes?

Kelly Reilly rounds off a year of nailing supporting roles opposite Hollywood stars by playing Dr Watson's girlfriend in Guy Ritchie's 'Sherlock Holmes'. But why is an actor who built her reputation working for directors from Poliakoff to Frears to Marber still playing second fiddle? The answer, she tells Craig McLean, is anything but elementary

Kelly Reilly gives good argy-bargy. She's had enough of overbearing, manipulative, condescending men and boys. The actress comes up against one in her returning ITV drama, Lynda La Plante's Above Suspicion, in which she plays Detective Constable Anna Travis – wallop, the sketchy journalist who seduced and betrayed her gets a cup of scalding coffee down his front. And she confronts another in her new film, Guy Ritchie's all-action reboot of Sherlock Holmes – sploosh, he gets a glass of wine in the face. No, I'm not talking about the geezer's geezer director. Although it seems the former Mrs Madonna does like to keep his cast and crew on their toes.

"Guy does this thing," says Reilly, a smile twitching round her lips, "when he basically thinks that he's rehearsed a scene and it's being lit and everyone's running around doing their thing. Then it gets to the point where he says, 'Right, that's enough now, I think everyone should be ready.' And he goes: 'TEN, NINE, EIGHT...'"

It was, she interjects, a happy set – "There was such great banter and respect" – a tacit rebuttal, perhaps, of newspaper reports of film studio-imposed reshoots on the big-budget heavyweight starring Robert Downey Jr as Holmes and Jude Law as the faithful Dr Watson. (Warner Bros, it should be noted, subsequently denied issuing any such demands.)

Then Reilly qualifies that: "I was literally on it a week, spread out over a month, so it's not like I got my feet under and realised what the set was really like. Most of the time I was just like..." – she freezes her luminously pale, freckly face in fear – "telling myself, 'Don't mess up!' Yeah," she laughs, "'Ten, nine, eight...' And everyone was just scrambling..."

In Sherlock Holmes, the 32-year-old from Surrey plays Mary Morstan, the girlfriend of Watson. "Basically, he's about to shack up with her. And my little story is that she threatens Holmes' and Watson's friendship. Holmes thinks his friend is gonna be moving out and getting all domestic and not going on any adventures any more and being boys together, and that I would be a threat."

Neither I nor Reilly – nor indeed anyone – have seen Sherlock Holmes at the time of our meeting in a central London hotel. So I wonder, does her Mary frown on the opium-smoking, derring-do and (one imagines, given that this is a Guy Ritchie movie) swiftly paced swordplay and fisticuffs?

"No, not at all. That's what's cool about her. She's very aware, and quite bright. And she probably just wants to be more involved. She has quite a bit of love for detective novels, and she's really excited about meeting Holmes. They have this dinner and he behaves horribly towards her, and he does a profile on her. It's not very positive. And she's like [here Reilly puts on a sarcastic voice], 'Oh, well done, very good, but you got something wrong...' So she puts him right and," Reilly beams with satisfaction, "throws a glass of wine in his face.

"She stands up for herself. And if they make Sherlock Holmes 2, I'd like to hope she might get a bit more involved because Victorian ladies, what do they do, they just sit home and drink tea and do sewing. It's so boring. Rachel McAdams [playing Holmes's "love interest", Irene Adler] got the main part, she gets to kick lots of arses. I just wear lots of nice dresses."

Reilly has a lot of prestigious roles and projects under her belt: Desdemona in Othello, opposite Ewan McGregor and Chiwetel Ejiofor for London's Donmar Warehouse in 2007/8; Stephen Poliakoff's Joe's Palace; He Kills Coppers, the 2007 TV adaptation of Jake Arnott's gangland thriller; the Royal Court's 2001 re-run of Sarah Kane's visceral and landmark 1990s play, Blasted; Joe Wright's Pride and Prejudice; Stephen Frears' Mrs Henderson Presents. So she knows a good part when she sees – or reads – one. Guy Ritchie, meanwhile, has made Lock, Stock and Two Smoking Barrels, Snatch, Revolver, RocknRolla and the soft-porn Swept Away. He has not written many – or indeed any – good roles for women. Did Reilly think about that before considering the role of Mary (which was offered to her without audition)?

"Well..." she ponders. "Yeah is the honest answer to that. It is a boys' film. The two women's roles are not exactly ones you would break your heart over trying to get. Unless you want to work with Robert Downey Jr and just do a cracking good scene with him, which is enough for me, thanks very much! And it was worth it. But as far as a female role that I want to attack and play and go very deeply into, I don't think that's the film I'm gonna find it on. Anyway," she adds sharply, in her curious, but believable mix of posh and slangy, "he should, though. He should write for women, and work with women." That's him told, then.

On the day of our meeting, Reilly is scuffing about in a lovely hotel suite. A Pink Panther film is on the telly. The door rings with a delivery of packages of clothes and accessories. Her sloppy jumper pulled over her hands, she accepts these gifts gratefully but also, it seems, a little self-consciously. She's awaiting this evening's West End première of her other current film, Me and Orson Welles, directed by Richard Linklater (School of Rock, Dazed and Confused). She plays an airy-fairy actress (very against type) alongside Zac Efron. The High School Musical alumnus plays a young theatre obsessive ' in 1930s New York, who finds a toehold in Orson Welles' Mercury theatre company. Young hunk Efron's appearance in the hotel lobby earlier caused a crackle of electricity. Reilly has just passed Christian McKay in the corridor. (The previously unknown British actor is a revelation as Welles.) He was, she smiles, overwhelmed by the hoo-ha. It was his first première; she counselled that he should "just enjoy it – you deserve it!"

And her attitude to premières? "I only get nervous because I never know what to wear. And I'd rather be comfortable. So I always end up taking my shoes off as soon as I get to the party as I can't walk in heels. I haven't been to one in forever, actually, so I'm quite looking forward to it. Yeah, if I'm organised and I feel comfortable, I can enjoy them. When I was younger I didn't really enjoy them. I found it too nerve-racking. But as I've got older I've chilled out a little bit."

Reilly grew up in Chessington; her dad was a policeman, her mum a hospital receptionist. Horses and drama were her passions. She began acting in her teens, having moved to London when she was 16. Roles on the stage quickly followed, and she landed an early TV role, aged 17, in an episode of Prime Suspect – after she inundated the drama's casting director with requests that they see her. She credits her parents with her work ethic and go-getting nature.

"It's ingrained. They both worked hard, and still do. I'm aware it's something that I appreciate in other people. It's just so easy to become blasé and be blind to how lucky you are if you have been given the opportunities I've been given. I am aware that tomorrow I could just be knocking at the Royal Court's door going, 'Hello! Anything going?'"

The actor Rafe Spall, son of Timothy, appeared on stage with Reilly in those early days, in an adaptation of A Prayer for Owen Meany. They also had the lead roles in He Kills Coppers, for which the 26-year-old Spall – playing a policeman – says Reilly's memories of her dad's work were a big help.

"Kelly's not vain, even though she's lovely-looking – she was happy to 'old up' in He Kills Coppers," Spall says of a story that spanned the 1960s and 1970s, "and I think that's harder for a woman than a man. I was 19 when we did A Prayer for Owen Meany, and I was always in awe of her as a young actor and a bit scared, because she was so good. She was a brilliant stage actress and an equally brilliant screen actress. She was everything you want another actor to be: enormously responsive, alive, in the moment and really lovely to hang out with. And she's got real acting chops: Blasted required her to go to all sorts of horrible lengths, which sets her aside from a lot of young actors. If she likes a project she'll wholeheartedly go for it."

Blasted, nods Reilly, "was one of the most amazing experiences I ever had on stage. Those years," she says, in which she also appeared in Patrick Marber's Strindberg adaptation After Miss Julie (a role currently being played on Broadway by Sienna Miller), "really shaped me. They shaped my taste, what sort of roles I wanted to play. For a while I got stuck in the darkness. I was playing harrowing, tortured characters. And everyone around me was like, yeah, maybe in a while..."

You'll be jetting off to Hollywood for some (in every sense) light?

"Yeah, and I did say a little while ago I'm looking for a bit more sunshine. But," she says brightly, "you get what you get!"

Or, if you're a talented and beautiful young English actress, you get what you want. Presumably Reilly – like Miller, or Keira Knightley, or Emily Mortimer – could have had the "sunshine" roles in Hollywood if she'd wanted them?

"Hmm, not necessarily true. People have this idea that because I am quite reluctant to embrace publicity or self-promotion that it's because I choose not to have that career. But it's not like they've been beating the door down and I've gone, 'No, seriously, I'd rather be doing much more earnest work for no money.' That's not the case at all. But I haven't put myself in that situation. Maybe if I had, after Mrs Henderson Presents, done big front covers and got a very famous boyfriend, that world could have opened. But (a), it doesn't sit comfortably with me and (b), I have to feel that I'm there for the right reasons. Otherwise I'm just not interested in it."

So she's an actor who can't fake it? "Yeah, basically! You know, I really enjoy longevity. I see actors in their forties and they just turn out these really fabulous roles and characters. You know who they are but you wouldn't necessarily know their names. They're gonna be around forever and they're really well-respected, but they can also go to the supermarket and don't need to be adored by the general public. That's the career I'd be really happy with." '

Accordingly, for all the hype that will attend the Boxing Day opening of Sherlock Holmes, Reilly would much rather talk about the new two-part Above Suspicion drama, sub-titled The Red Dahlia, which airs in January. Anna Travis is a role she feels she can do good work with.

"I didn't know what I was doing on the first one. It was a real stab in the dark," she admits of the initial two-parter broadcast in January this year. And Reilly is as refreshingly direct about what she sees going on around her. "I did feel that the confidence behind it was experimental from ITV. Just everything about it was, 'Well, yeah we're gonna try it but we'll see...' Then as soon as the ratings went through the roof and it was well received, of course everyone was like, 'Oh, we knew...' Shut up! No one knew! I didn't know! It could have been awful. And it still can be better.

"I was adamant not to commit to more for that very reason. And I was also, to be honest, nervous about taking on a role that I'd have to repeat, because I've never done that, not even on stage."

This feistiness oozes out of the screen in The Red Dahlia. DC Travis is investigating a killer hellbent on aping the gruesome murder of a victim dubbed the Black Dahlia in 1940s Los Angeles. When she's taken for a ride by a crime reporter, thereby compromising the investigation, Travis's no- compromise demeanour swiftly kicks in.

"Kelly has taken on board the character and has brought to the role humour and yet a totally believable quality of a young, career-minded police officer," observes Lynda La Plante. "She has retained a freshness throughout and her appearance in The Red Dahlia proves that she is developing as a major talent. She has learnt to get beneath the skin of Travis and never misses a moment. By this I mean that, if she is not central to a scene, you can see her always attentive. It is surprising to find how many actors lose concentration, and 'listening' is central to a role. I think she is a star and I feel very fortunate to have Kelly on board."

Nonetheless, Reilly wanted to be sure that, post-Prime Suspect, Travis wouldn't just be Jane Tennison redux. "Oh God yeah! I didn't even like the idea that they were even talking about it being the next Prime Suspect. What's the point of everyone comparing Tennison and Travis – they're just so different..."

Difference and artistic progress, those are what matters for Kelly Reilly. Rafe Spall recalls that, "That's something she always told me: her CV was very clean." That is, the right parts for the right reasons.

So, a couple of days after the Me and Orson Welles première, she's heading to Rome, to film the low-budget Italian film Meet a Friend. "A nice little English character, in Italy, with a bunch of lovely Italians, completely charming."

Reilly is sparky and engaging company. She keeps the PR fuss of première day at arm's length, is make-up free and jewellery-light. Indeed, there is no sign of an engagement or wedding ring – she and her fiancé, the Israeli actor Jonah Lotan (he was in HBO's Iraq war drama Generation Kill) were supposedly getting married last year. Telling her that I want to get my facts right rather than pry, I inquire gingerly, are they still together?

"I'd... rather not talk about it. Only because I'm trying to protect myself and my life. I'm sorry, I don't mean to be... but ah, it's not, it's a bit complicated."

Another function of the actors' pillar-to-post lives?

"Yeah," she nods, "yeah."

But to come back to her looming – if limited – blockbuster splash. If Reilly's attitude to the roles she takes might be summed up as "No shit, Sherlock," why take the role of Mary?

"Honestly? Robert Downey Jr. It's not a job that you turn down. It's real quality. It was just a nice offer. It was a year of real... cameos, if you like," she acknowledges, also mentioning her forthcoming appearance in Triage with Colin Farrell, in which she plays the pregnant wife of a photojournalist who is killed while covering a war.

"As much as I love getting characters I know I'm going on a real journey with, and I know it's gonna take a lot of time, and I know my [personal] life has to get put aside, these same roles where you can just drop in and out, they're so much fun. You get to have a lot more different experiences. I really enjoy that variety."

But now, after "a year of cameos", she's ready to change it up again. "Now I'm going for the film role that I can run with and get lost in." Financing issues meant Lost For Words, a Working Title romcom with Hugh Grant in which she played a translator, fell apart right before shooting – "which was a shame because I was learning Mandarin for it, and you don't just do that overnight!" A similar fate befell a Dylan Thomas biopic in which she would have played the poet's wife opposite Kevin McKidd. "I turned down a lot of work for that film," she says grimly. "And I really wanted to do it. 'I think Caitlin is a cracking part, and it would have been the complete opposite to The Edge of Love," she says of the biopic that starred Keira Knightley and Sienna Miller. "Ours," observes cool, clever and deftly direct Kelly Reilly, "would have been much less pretty."

'Sherlock Holmes' (12A) is released on Boxing Day