Dirty girl

Cox acknowledges that much of the attraction of playing Spiller was that, superficially at least, she is the polar opposite of Monica. "I love it that she is outrageous," she says. "You want her to be bad."

Bad is something of an understatement. In one show, Cox's character sets up a married baseball star by arranging for him to have kinky sex with a hooker who is pretending to be a fan, then taking pictures of the act that she plans to publish.

What will be most shocking to Cox's Friends fan base, however, is how blushingly racy Dirt is - and how brazenly sexualised Cox's character. In one episode, she is shown alone in bed, reading magazine proofs, while masturbating with a vibrator. (Yes, Monica with a vibrator.) In another, she is seen indulging in a one-night stand with a barman, whom she subsequently ejects from her apartment with the help of a Taser stun gun.

Then Spiller meets a young guy who, for the first time in her life, brings her to orgasm. "When we first came up with the idea that Lucy can't really be pleased by anyone but herself, it was intended to show that it's the opposite of what it would take for a man to be satisfied," Cox says. "One of my favourite movies is Network [set in the world of American television].

I love the scene where Faye Dunaway says how she always orgasms so quickly, because she is like a man in the way she deals with things.

"I thought it was an interesting turn for this woman, Lucy Spiller. She's so self-sufficient, such a control freak, that she can't let go enough to have an orgasm by someone else. Then she meets this young guy, and all of a sudden he has control over her, because that's her first time. We definitely pushed the envelope on the vibrator, perhaps a little too much. I ought to have cut out some of those scenes."

Orgasms aside, Dirt dovetails neatly with the new obsession of American TV drama - the high-powered career woman. Like the other big US show of the moment, Cashmere Mafia, which charts the lives of four New York-based female executives as they juggle their private and professional lives, Dirt gets to grips with the conflicting and conflicted demands of life at the top.

Cox believes there are more similarities than may seem apparent between Monica and Lucy, similarities that reflect her own personality. "They are both strong and intense women," she says, "but one is just more of a kook. Monica manifested her controlling nature by being a neat freak. And Lucy has good sides to her: she's vulnerable, she's doing the best she can, and she doesn't know any other way than to be this kind of shark that she is. Her justification is that she needs to 'reveal the truth'; she wants to get answers.

"I can relate to that," Cox continues. "I like the truth too. My favourite word is integrity. It's so important to me. I can handle anything if I have the truth. I think that's how I relate to Lucy."

Like most Hollywood stars in recent years, Cox has been the subject of sustained tabloid interest - though her particular celebrity trajectory has spared her the microscopic scrutiny to which her best friend and former co-star, Jennifer Aniston, has been exposed. Her role in the most popular television comedy of the past two decades has made her a hardened pro when it comes to the celebrity game, and she accepts that having her photograph taken is part of being famous. She draws the line, though, at people trying to get pictures of her three-year-old daughter, Coco. "We were leaving a restaurant the other night and there were so many paparazzi," she says. "And Coco was like, 'Why's everyone taking my picture, Mommy?' And I said, 'Coco, it's because mom is on television.' The first time you see your child flinching from the flashes is strange."

Given this kind of media intrusion, Dirt is what her therapist would probably call "empowering", even if Cox - who co-produced the show with her husband, David Arquette - insists that this is not her way of getting her own back. "I may have a lot of experience in the tabloid world, insofar as being written about, but it is not revenge," she says. "The original idea was a paparazzo who was willing to do anything to get the story, the lowest of the low, a 'go through your trash' kind of guy. But when we took the idea to the TV network, they said they wanted to centre it around a tabloid-magazine editor. And I said, 'I want to be in it.'"

To research the role, Cox met a number of female tabloid editors, including Rebekah Wade, the editor of The Sun. "She's a fascinating woman," says Cox. "She is a very powerful, strong woman. I learnt a lot from her, and I like the way she dresses. She was very fitted."

But Cox admits that her visit to The Sun's offices was disturbing. As she walked through the newsroom, an editor called her over.

"He said, 'Courteney, do you want to see what you've been doing for the past couple of weeks while you've been in Europe?'" she recalls. "Then he showed me pictures from the week before, when I had been in Sardinia, pictures of when I left the London hotel I was staying in half an hour before, pictures of me in my car, pictures of me arriving at The Sun, even a shot of me opening the door to The Sun five minutes earlier."

Besides the fact that she relishes playing a character as racy as Spiller, part of the pleasure of Dirt, says Cox, has been working so closely with her husband. Just that morning, they had been sitting in the "writers' room", sketching out plans for a second season. Cox says they each bring contrasting things to the show. "David and I are very different, and we have different creative choices and different creative views," she explains. "He's really left of centre; it's amazing what he comes up with. I'm good with the emotions and psychology of people; he's good with other creative aspects, like Don's hallucinations." One of the show's strongest characters, Don, is a paparazzo who is schizophrenic.

The varying sensibilities Cox and Arquette bring to their jobs as producers reflect their differences as people. And the fact that they argue openly about their views may have led to rumours in the tabloids, in recent months, that their marriage was going through a rocky patch.

"Yes, I do bring things home," Cox acknowledges. "It's time to catch up, because when you have been working together, you don't really have time to talk about what happened. At dinner, there is a lot of catching up to do, even though we have seen each other most of the day. It's weird."

Even Cox and Arquette acknowledge that they are one of Hollywood's most unlikely couples, and that it has been tough to work through their problems. Arquette, who is seven years younger, loves to goof around, while Cox admits that she finds it hard to relax. She renovates and redecorates homes as a hobby, and has made tidy amounts of money from it, although nothing like the £500,000 per episode she made for each of the last two seasons of Friends. Earlier this year, the couple put their Malibu home, which Cox had restored, on the market for £16.5m. Cox is also more direct, organised and energetic than Arquette, who is avowedly off the wall. Their differences are apparent even in their stylistic choices: Cox is elegant and classic in her dress, as she is on the day we meet; Arquette has often been seen in outfits that wouldn't look inappropriate on a clown.

They both say, though, that their relationship has strengthened over the seven years they have been married, not just through their joy at the birth of Coco after many earlier attempts to have a baby, but through tragedies they have both suffered, including the death of Arquette's mother and of Cox's father. They have also watched as the marriage of their closest friends, Jennifer Aniston and Brad Pitt, fell apart. They signalled their own determination to see their relationship through hard times with wedding bands that say: "A deal is a deal."

And if the tabloids want to concoct problems that may not be there, Cox knows better than ever that the Lucy Spillers of this world "have a job to do, and I understand that". But hands - lenses - off Coco.

COURTNEY LOVES . . .

Jennifer Meyer 'I adore her jewellery' (www.jennifermeyerjewelry.com)

Stella McCartney Skinny trousers, £275

Red wine 'I like a nice Silver Oak' (£54, from www.thesecretcellar.com)

Balenciaga 'My favourite shoes' (£775, from Harrods)

A rose-gold Rolex 'Right now, it's what I want' (Datejust watch, £10,100)

Laura Mercier make-up 'I'm a big fan'

Dirt starts tomorrow at 9pm on Five US