They sit in their cars, faceless and nameless, cowards hiding behind this big lens, which is Freudian enough in itself, and they steal from women..." Sienna Miller is referring to the paparazzi, who she says made her life intolerable for years. She was door-stepped, spat at, verbally abused, harassed and stalked every night by groups of men who made it their business to be as hostile, frightening and provocative as possible. She was under constant surveillance. "It got to the point where I was agoraphobic. I didn't want to leave my house."
These days she is left alone. No one followed her to the bar in London's Connaught Hotel where she now sits beside me, shoes off, legs folded, tiny in a leather armchair, all golden and smiley and the personification of pretty. There were no men lurking outside her house when she left. She can now travel on the Tube, walk her dog in the park and visit her friends unhindered. She rarely features in the red tops or celebrity weeklies anymore and not because she has become any less riveting to the public.
After she waged war on, and won a restraining order against Big Pictures, Britain's biggest employer of paparazzi, her life changed in an instant. "From one day to the next I went from feeling hunted and paranoid and terrified and insecure, to no one harassing me."
Miller, now 29, may be best known as Jude Law's adorably girlish paramour, as the pretty girlfriend in several movies and fashion's favourite muse, but over the years she has acquired a fearsome reputation for being ruthlessly combative with the press.
She won numerous harassment and invasion of privacy cases against the tabloid press, including a 2008 settlement against Darryn Lyons, aka TV's Mr Paparazzi, spurred on no doubt by a programme he made, which was charmingly entitled Stalking Sienna, in which he admitted to the primal pleasure of hunting his prey. (Ironically, Lyons has recently engineered a move towards personality status with an appearance on Celebrity Big Brother.)
Miller filmed photographers in pursuit of her with a secret video camera, disguised as a lighter, so that she could show the judge, who was visibly shocked, how they routinely tried to cause accidents, swore at her and backed her into dark street corners. As a result of her court action, it is now unlawful for them to sit in wait outside her house, to follow her or take photos of her anywhere she can reasonably expect privacy. Thanks to her, there is now a precedent to protect others from similar intrusion, which Lily Allen and Cheryl Cole have both since made use of.
Miller's most high-profile, high-stakes battle with the press, though, has been with Rupert Murdoch's News of the World, which she suspected for years was illegally hacking her mobile phone to find out the most personal and salacious details about her life.
Until now, she has been very reluctant to talk about it, despite the fact that she was, in the words of a fellow hackee, Hugh Grant, "the real heroine and first one out of the trenches, walking towards the machine guns". Contrary to the popular canard used as defence by the tabloid press – that an actor's success depends on publicity – her virtual disappearance from the tabloids has, she says, benefited her career. She has six films currently awaiting release.
"My career suffered massively because I had a reputation for being a very tabloid person. I have seven years of articles I have to overcome. I lived my twenties in a very public manner and if anyone's twenties are documented it's not always going to be pretty. With acting, there is a level of anonymity which is conducive to your profession. There are examples of very public people who are on the cover of every celebrity magazine but can't open a film."
Miller has only agreed to give this interview because she is now one of the core participants in the Leveson public inquiry into phone hacking and media ethics and because she is frustrated that her victory over News of the World has been portrayed as a capitulation on her part. "I was upset that it was reported as if I had just given up and settled. The real position is that there was nothing left to fight in court. In my case, and my case only, they admitted full, unconditional liability on every part of my claim. That's why I applied for and obtained the first judgment against News Group."
As well as assisting with the Leveson inquiry – alongside the parents of Madeleine McCann, actors Hugh Grant and Steve Coogan, Harry Potter creator JK Rowling and former Formula One boss Max Mosley – she is also preparing to be a key witness in the civil action which is starting at the end of January 2012.
Hugh Grant and Steve Coogan may have recently taken impressive turns each with the baton, but it was Miller who started all the trouble, back in June 2010, when no one else dared. It was her case that was name-checked by both Rupert Murdoch and Rebekah Brooks in the Select Committee hearings.
For someone who has lived through so much scrutiny, from such a young age, Miller is unexpectedly normal. She started out predictably as a model just out of her teens and quickly progressed to film work – most notably Layer Cake, Alfie, Factory Girl and The Edge of Love – and theatre roles including As You Like It and After Miss Julie, in London and New York.
She understands that it is hard for the general public to sympathise with an actress who is famed worldwide, "especially when they see you with your first-class ticket and Burberry bag", and is the first to acknowledge that "when you know they've stooped so low as to hack a murdered girl's phone, it kind of puts all our complaints to shame". Her story is nevertheless unsettling, even for those who are familiar with the tactics of the tabloid press.
Miller had become increasingly agitated about the idea that someone close to her was leaking stories to the press. "I changed my mobile number three times in three months. There were clicks on the line. I would pick up the phone and it would drop, there were messages I would never get, coupled with articles [containing private information] coming out every week. It had been going on forever, long before 2006."
There were more intimate stories that appeared in the papers, which only her closest family and friends knew about. "So I started to do tests. I would leave messages on people's phones, like we're going to rent this house or whatever, and it would appear the next day in the papers."
There were more intimate stories that appeared in the papers, which only her closest family and friends knew about. Eventually, she says, "I sat down in a room with my mother, my best friend, my sister, my boyfriend, and said someone in this room is lying and selling stories and one of you has got to admit it."
When the hacking story emerged five years ago, it confirmed her suspicions and she decided to take legal action.
Initially, she admits she was nervous. "Everyone was scared of Rupert Murdoch, even governments. People are terrified for their own reputations. They want the press on their side." She decided to act at a time when no one else dared, regardless of the consequences, she says, because she was unable to stand back and do nothing.
"The tabloid media culture in this country had got to a point where it was completely immoral. There was no consideration for you as a human being. You were successful, you were making money, therefore you deserved it and it was a very medieval way of behaving. I realised I couldn't continue living in this country and do my job, which I loved. You want to feel that you can do something creative that you love without being picked apart and mutilated for other people's pleasure."
Does she think that the tabloids reflect or inform? I ask. "Both." Part of the problem, she believes, lies with British society's "hunger to see people reduced, which is bred by the tabloids".
I'm interested in whether she has grappled with the seemingly conflicting issues of privacy and freedom of information. Is privacy absolute, in her opinion? Miller concedes that it's complicated. On one hand, she agrees that a democracy depends on a free press, on the other, she has seen how that freedom has been abused to peddle what she calls "tittle-tattle".
She's an odd mixture of prefect's manners and naughtiest girl in the school. She arrives on time, enunciates her words, is scrupulously courteous, suggesting we move to a quiet corner of the bar for the sake of my tape, and offers to pay for our drinks. Meanwhile, the rebel in her is enjoying "the revolution". "I think the media has changed, not just in England but in the world," she says, eyes gleaming.
Miller has undoubtedly been one of the catalysts for that change.