This was a two-act drama, punctuated by an intermission in which Sienna Miller apologised repeatedly for not giving a good enough performance up to that point. For the first hour she’d been matey yet defensive, in the way most actors are on these occasions, both of you maintaining the fiction that one of you is not really a member of the mistrusted press while the other one doesn’t say very much.

“I’ve been having these warnings,” she says. Her mum, for instance, has told her to “be more mysterious” in interviews. Other advisers have said, “‘Don’t do this, don’t do that’, because I always put my foot in it”. What she put her foot in most recently, in a piece in Rolling Stone, was Shitsburgh, in reference to Pittsburgh, where she had been filming. She has also said people take drugs because “they are f***loads of fun”. She got some stick for that, too.

So she’s on best behaviour today, trotting out stuff about how her latest film, Interview, is “a real actor’s piece”, with a “European feel”, and how director and co-star Steve Buscemi “created an environment conducive to creative freedom”, all of which may well be right and true and beautiful, but isn’t what we came here for.

Miller is a good enough player (I think she may turn out to be an exceptional one) to sustain a light frostiness well into the second side of tape, but it takes only a tap for the ice not so much to melt, but shatter and evaporate. I ask if she doesn’t like doing interviews, and she says: “Why? Do I not seem like I do? Am I being a really bad interviewee? Am I being really boring? I’m sorry. I’m ill, I am actually quite ill [she snuffles mightily into a tissue] and we’re in a funny room. I’m really sorry.”

The funny room in question is a photographic studio in West London. We’re on a PVC sofa in one corner, an hour into our allotted time. The guy on reception has already popped in to say that her car is outside and we’re into overtime. “Schmovertime,” she giggles. “This is like being at a shrink’s office, isn’t it? A seedy shrink with a PVC sofa.” Fancy a drink, asks the seedy shrink, eyeing the fridge full of free booze. “Are you having one?” I will if you will. “Shall we have a beer then?”

I say it’s not that you have been boring so far, perish the thought, but I can’t deny there’s a gap between my expectations and the reality. She splutters into her Bud: “‘I was expecting you to be really great and actually you’re shit’, that’s basically what you just said.” No, no, I say, it’s just that everyone says you’re...? “The biggest gob in Hollywood?” And yet you seem...? “Talking about the Jude thing,” she says, “it would just make him angry, it’s not fair.”

“The Jude thing” is her broken engagement to Jude Law, cause of a substantial media firestorm in the summer of 2005, when barely a day passed without Miller, then just 23, scurrying away from the pack as fast as her Ugg boots and assorted belts, scarves and bags would allow. Interesting, given what happened, that it’s her who’s worried about making him angry.

It was, in any event, a brutal business (“hideous, awful, very hard to deal with, sink or swim”), one from which she emerged with a great deal more credit than either Law or my trade, let alone the tragic souls who frequent internet gossip sites. (Peculiar places these sites: for all the modernity of their form, their content suggests that the 18th century notion that actresses are no different to whores is alive and well.)

Law publicly apologised to his fiancée when it emerged that one of his children (by ex-wife Sadie Frost) had caught him in bed with the nanny. Law and Miller split, reformed, split again. “It was a really great relationship in a lot of ways,” she says. “I don’t regret it.” Does she spend interviews just waiting for the Jude thing to come up? “Well, you do feel, ‘God, does that define me?’, and that’s depressing.”

My guess is it won’t define her for much longer. I put it to her that Law has had a bad couple of years professionally. “Go on,” she says carefully. Couple of turkeys, yeah? “So it’s my fault?” she laughs. Obviously he’s still a big star, I continue, albeit a big star in need of a good role, and she was a “What’s she ever done?”. But now, she has had two great roles (Edie Sedgwick in Factory Girl, Katya in Interview), has three films awaiting release, a Bafta nomination and is off to LA to shoot a big action pic. “Well?” she says. Well, later this year, or next year, Jude Law could be that person who had a thing with Sienna Miller rather than the other way round. “No!” she squeals. “Oh God, you’re such a bastard! No, you’re not! Oh no, that was a joke. ‘She called me a bastard, the abusive cow! The cowlet!’ I don’t think that’s true in any way.”

If it were my ex, I say, and their film bombed, part of me would be thinking “hee hee hee”. “You must have [corny American accent] resentment issues with your exes.” And you’re not like that? “No, I’m not. I don’t wish ill on anyone. I genuinely am one of those people who want other people to succeed. It’s not a conscious choice, it’s just the way I am. I’m not hugely successful so it’s not as if I have some massive take on this but a lot of people assume you have to be a bitch. I disagree completely. It’s a massive case of luck.”

Maybe, I suggest, if anything, she is too much the other way, a people-pleaser. “Yes, I am massively.” I mean, here she is, feeling bad because she has given me a duff interview. “Yes, and most people would be ‘F*** you’, chuck the beer over you.” She’s been told to stick to discussing her work, “but [although] I don’t want to be defined by the public image that has been invented for me, deep down I do feel defined by it so when it comes to doing an interview about work, [I think] why would anyone really give a f*** about work?”

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