Sarah Harding rolls her eyes, crosses her arms, and gives us a look we imagine she perfected while playing a sulky schoolgirl on the set of her new film, St Trinian's 2. We've asked about her party-girl reputation. And that, she insists, is just not her these days. She's using a year off from Girls Aloud to get herself taken seriously - both as an actress, and as a person, too.
"People are so stuck in the past," she sighs. "Why is everyone obsessed with my drinking? I do have another side. But people don't pap me going to business meetings or cooking dinner. That caner tag, it's not me and I'm sick of it."
We're confused. At today's shoot a newspaper lies on the table, showing a picture of Sarah, 28, coming out of her favourite London haunt, Mahiki, with Marvin Humes from JLS. "It was a business meeting," she says adamantly. Because as well as being an actress - she's here to talk about her latest role as school rebel Roxy in the St Trinian's saga - Sarah is using the Girls Aloud sabbatical to discover her inner entrepreneur. Along with the owners of royal hangout Mahiki, she's invested money in London's hot new nightclub Kanaloa. An interesting move for a girl once dubbed the Camden Caner because of her penchant for the notoriously boozy north London social scene.
"The club wasn't a reason to go out and party, but a business opportunity," she explains. "There comes a time where you have to grow up. I don't enjoy going out as much as I used to. Maybe it's because I'm in a relationship now. When I was single I loved being around people, but when going out becomes monotonous, what's the point?"
These days, Sarah's happiest at her Buckinghamshire home playing Grand Theft Auto on her PS3 and cooking home-made meals. Food's a recurring theme in our conversation and Sarah's face falls when a huge dish of lasagne arrives for lunch - she's on a self-imposed carb ban today. Her last argument with Tom Crane, 30, her DJ boyfriend of two-and-a-half years, was about what 'baking blind' meant. And apparently her friends call her 'Mama Hardcore' - the party animal who makes her own pasta.
The Sarah we see today is a far cry from the wild girl we met 10 months ago when she graced one of our January covers. She arrives an hour late, dressed in a baggy T-shirt, leggings and Uggs. Her clothing choice is to hide the paunch she says she's developed since the band took a break. She lifts her top to prove her point.
"That's usually a six-pack," she moans, even though we can only see a barely there curve on her size-8 stomach. "It's the change in weather. Me and Tommy are all about comfort food. It's nice though, I've got a bit of insulation!"
Funny and self-effacing - so far, so Sarah. But after four hours (yes, that's four hours) in hair and make-up, Sarah has been transformed into a sexy screen siren. Her conversations are peppered with stories from the St Trinian's set - of Rupert Everett giving her acting advice, and practising lines with Colin Firth.
Sarah's career switch comes after almost seven years in Girls Aloud, the band that formed in 2002 after winning Popstars: The Rivals. Countless hits, six albums and umpteen awards followed, including a Best Single Brit in February for their song The Promise.
Even apart, they remain in high demand. Cheryl Cole, 26, is now the undisputed nation's sweetheart as an X Factor judge and solo artist, recently bagging a No1 single and album. Nadine Coyle, 24, lives in LA and will launch her solo material next year. Nicola Roberts, 24, is focusing on her beauty range, Dainty Doll, and making waves in the fashion world; while Kimberley Walsh, 27, is pursuing TV presenting offers as well as negotiating fashion and beauty deals. Sarah, cannily, is avoiding comparisons with her band mates by setting her sights on an acting career.
While she's written and recorded songs for the St Trinian's soundtrack, that's where her solo career begins and ends. "I'm not in a rush," she says. "Cheryl and Nadine are both doing the solo thing, but I want to take my time. I don't know how Cheryl squeezes it all in - I'd be having a breakdown by now."
What does she think of Cheryl's debut album, 3 Words? "I haven't heard it yet," she admits. "I heard the new single the other day, that's quite good. I'm really proud of her."
So with the girls going off in different directions, are cracks appearing in Girls Aloud's foundations?
"It was a relief to be apart for a while," she says. "As much as we love each other, we were getting on each other's nerves. All we did was moan about being knackered. There wasn't any gossip because we saw each other constantly. These days we've got more to talk about and we appreciate each other more."
But the differences between Sarah and the others remain.
"I'm quite loud at times," she grins. "The girls think I've got a potty mouth. I've worked in male-orientated jobs before and never had sisters so I've got quite a male sense of humour. Something I might find funny, Cheryl will go: 'That's gross!'"
"I've got loads of different sides," she adds. "I go into different personas, but that's why people always said I'd be good at acting. When I'm on stage I'm lairy, but when I come off, sometimes I just go straight home to bed."
Sarah admits it's hard for Tom to understand the person his girlfriend really is. "We're always having debates," she says. "We're either best friends or worst enemies. We have a tempestuous relationship. He thinks I'm bipolar and mental and calls me 'nut-nut'. We're quite feisty, but that makes us. If he was a doormat, he'd have been gone ages ago."
The couple split for a week last year, with Tom blaming work pressures. So we wonder where he fits into Sarah's new less-pressured life. As a resident DJ at Mahiki, he's immersed in the party scene that she says she's left behind. So does Sarah worry that, while she's at home cooking, Tom might be tempted by the DJ groupies? Cue Sarah the actress.
"I do play the jealous wife sometimes because I've got to make him feel secure," she says. "He's probably more jealous than I am, but every morning we wake up in the same bed. If we didn't, there would be more trust issues."
Three months back, Tom moved from his north London home into the Buckinghamshire pile Sarah bought last year. And, it seems, Sarah's got a pretty good catch. "Tommy's like a house husband," she says with a grin. "I came home the other day and he'd made a steak and ale pie!"
So, the question begs, is he The One? "I don't know," she says. "He's definitely a contender. I'm focusing on my career. I want to be able to stand on my own two feet before I can think about marriage. We're like a married couple anyway."
In more ways than one it seems. "We're too tired for sex," she jokes. "It's good because I have other things to do before babies. If I do that now, what do I have to look forward to?"
Sarah's manager's baby, Felix, has everyone at the shoot oohing and ahhing, and between takes she grabs cuddles. "I don't know how I'd cope with childbirth," she says, grimacing. "I'm petrified. And morning sickness scares me too. I'm also a good old-fashioned girl and I'd like to be married first."
Sarah's bitter rift with her dad John must make her somewhat cynical about family life. She disowned him at 18 and changed her surname from Hardman to Harding. Sarah doesn't want to talk about him today and her silence speaks volumes. "My friends are my family," she says. "I was lost for quite a long time - that's probably why I went off the rails a little bit."
Sarah left school at 16 without any GCSEs but with a huge dream of being a star, and she's now working hard to fulfil her acting ambitions. As well as elocution lessons, she's having sessions with an acting coach, determined to quash criticism she'll only win roles because of her profile.
As well as St Trinian's, Sarah was in BBC2's Freefall alongside Mamma Mia! hottie Dominic Cooper. Although she's the first to admit she's got a long way to go, she's already been up for a role against a big-name star.
"There was one part I went for, but I think they were punching below their weight when they asked me because they gave it to a Hollywood A-lister," she reveals. "I'm sworn to secrecy, but it was really good to just meet the casting director and the director is happy to keep me in mind. My agent thought it was good experience for me.
"My worst fear is forgetting my lines," she adds. "And I'm my own worst critic. I cringe every time I watch myself. I'm not saying I'm going to be the next Kate Winslet - that doesn't happen overnight - but I'd love to do a Charlize Theron in Monster. I like to do things that will surprise people.
"Some people expect you to fail - I hope to prove them wrong. People say: 'She's playing a schoolgirl and she's pushing 30', but it's a bit of fun. Rupert Everett is playing a woman! People take things too seriously."
But taking things seriously is exactly what Sarah's about these days. Actress, country bumpkin, nightclub owner - she's determined to succeed at all of them. But, for now, as our shoot ends, she's off to Guy Ritchie's pub, The Punch Bowl for another of those business meetings.
St Trinian's 2: Legend Of Fritton's Gold is at cinemas nationwide from December 18.