Minnie adventure: Miss Driver turns her attention to country music and motherhood

She's conquered Hollywood, stars in a hit TV series, and is one of Britain's most successful acting exports

Minnie Driver is having a spot of bother with her guitar. "I don't need a strap any more," she laughs. "I can just rest it here." She lays the instrument on her pronounced bump and pats her belly affectionately. There's no disguising it: Driver is six months pregnant and expecting her first baby in August. But before that comes, the delivery of her second collection of songs on an album called Seastories.

We might know Driver best as one of our more successful ex-pat Hollywood actresses, but she was a musician long before she turned to acting. And, having overcome initial scepticism to win enthusiastic reviews for her first album four years ago, she's back with a new one. It's not just a vanity project either – her impressive supporting cast includes Ryan Adams and his band The Cardinals, as well as indie singer Liz Phair. And a fine effort it is, too, Driver's warm, smoky voice perfectly suited to a set of melodic self-penned songs of love and heartbreak, inspired by a failed relationship.

With their country flavour, it's the sort of thing you might expect from Sheryl Crow, or perhaps from Dahlia Malloy, Driver's trailer-trash character in the hit TV series The Riches, than from a very English former public schoolgirl – albeit one who now lives in a trailer park. An avid surfer, Driver's current home is in a "double-wide" mobile home in a cliff-top trailer park above Malibu beach, chosen because it overlooks "the four best breaks in Southern California". She lives with her dog, Bubba, in a community of young families whose passion is for the waves rather than showbiz gossip.

It's a far cry from boarding at Bedales School in Hampshire, where Minnie, 38, was sent at the age of seven when her parents split up. It was there, aged eight, that she made her acting – and singing – debut, winning the lead role in a school musical staged as a protest against plans for a local bypass. "We wrote a musical called Bypass The Parcel and I auditioned for the part of the solo singer and got it," she recalls happily.

She even made it on to the news. "There was this 300-year-old oak tree that was going to get chopped down and BBC Nationwide came down and filmed me up the tree, with my hippie English teacher Bob playing the guitar at the bottom. The camera panned up the tree and you saw these little legs, and then this kilt that I was wearing, and there I was perched in the tree singing a song about this beautiful tree." And was the protest successful? "Yeah, we staved off the bypass for 10 years – and then they rerouted the A3 right through the grounds of the school!"

Today she's wearing tight black leggings and a T-shirt with a picture of Gandhi, inscribed with the motto "Be True", that would be baggy were it not stretched over her growing bump. Freckly beneath her chestnut mane, and with huge hazel eyes, she radiates the healthy glow of an expectant mother. She's prepared to talk about it too – but not before she's satisfied her daily craving for a cheese sandwich at precisely 11.30am. "This was an unplanned pregnancy," she confesses between bites, "but it's been very happily received by everyone. Which is great," she adds with a wide smile. "It's something I've wanted to do my whole life; I can't believe I've waited this long."

There are no rings on her fingers and she is adamant that she has no plans to marry before the birth of her baby. "Definitely not in the near future," she says. "It's not important to me. I don't think a piece of paper lends itself to the idea of being a good parent and I want to be a good parent."

She has so far kept the identity of the father a mystery, prompting much Hollywood gossip. She won't be drawn on revealing him now but she does say that it's not the man named in many reports, San Francisco musician Craig Zolezzi. "Craig's not the dad!" she exclaims. "He's my great friend and he's been so cool about it. I want to shield the baby's dad as much as I can because it wasn't his choice to get roped into all this stuff. It'll come out in time and there'll be some other bump people will be interested in and I'll have this baby and get on with my life."

The only clues Driver will offer about the identity of her "baby daddy" are that he is English, and "sort of in the same business", and that they have evaded detection because "he's really busy, like me". She is so far undecided whether to have her baby in England or the US: "A big part of me wants my child to be English. My family are here and I'm sure I'll move back here one day. It's just that my work, and the opportunities I've had, have been so varied and wonderful in the States that I've just followed my nose really. There's an ease living in America, and you're judged far more harshly in Britain for your artistic endeavours. But," she adds, "obviously politically, in America, it's a..." she searches for the right words, "bloody mess."

Driver insists she saw her career being in music until she was side-tracked by acting. After Bedales, and finishing school in France, she enrolled at the Webber Douglas Academy of Performing Arts in London. Upon graduation, she juggled television roles – Casualty, Lovejoy, Maigret, Peak Practice, House of Eliott and Knowing Me, Knowing You With Alan Partridge – with singing in the Milo Ross Band. "It was just pre-Massive Attack, with the same sort of vibe – rappers, and me singing the choruses. But we made a terrible record and drank most of the development money."

The band were dropped without releasing their album and Minnie moved to Uruguay, "to sell vintage jeans on the beach to rich boys from Buenos Aires", with her sister Kate, who is now her partner in the film production company Two Drivers. Her fortunes changed dramatically when, following a call at the local post office, she was summoned back to London for a meeting with EMI, who were interested in signing her up as a singer. "I really thought that was the direction my career would go in." But in the same week she was asked to audition for an independent Irish film, Circle of Friends, and was cast as the frumpy Benny Hogan, who wins the heart of the local heart-throb (played by Chris O'Donnell). She put on two stone to play the part and the low-budget picture proved a surprise hit, launching her screen career.

Before long she had become a Bond girl, playing "a bad Russian country-and-western singer" in Goldeneye, followed by more impressive roles in Big Night, Sleepers (as Brad Pitt's girlfriend), and Grosse Point Blank (as John Cusack's on- and off-screen girlfriend). Her big break came in 1997 with Good Will Hunting, which brought her an Oscar nomination and kindled a high-profile romance with Matt Damon that notoriously ended four years later when he announced their split on Oprah – without telling her first.

Looking at Driver's film CV, two things stand out: she has never played the same sort of character twice, and she has chosen her films on merit rather than their commercial potential. "There have been big budget things I said no to, but I stand by every single choice I've made, including the choice not to work," she says with conviction. "There are troughs and peaks in careers, and there have been times when there were jobs that I wanted that I haven't been able to get because I didn't maintain my profile or it was somebody else's time. But I believe in longevity, and I believe in talent and the love for what you do."

Driver has no time for complaints that there are no good film roles for women approaching 40, saying: "You can subscribe to all of that but down that road lies plastic surgery and a miserable life. You have to look at yourself as an actor; you have to look at yourself as an artist. But, having said that, the best roles for women are on television these days."

This includes her lead role in The Riches, a comedy drama about a family of gypsy con artists – headed by Driver and Eddie Izzard – from the American South who live the high life by assuming false identities. Her character, Dahlia Malloy, is pure trailer trash – "total trashy whore!" enthuses Driver – an ex-con with a drug habit who flounces around their gated community in tarty dresses, slurring vulgarities in a thoroughly convincing southern accent. "It's brilliant!" laughs Driver. "It really is the best part I've ever had, and I love it to pieces. I don't want it to stop."

Driver has been nominated for Emmy and Golden Globe awards for the part but, despite garnering higher ratings than critically acclaimed shows such as Mad Men and Weeds, the cast is currently waiting to hear whether a third series will be commissioned. If so, Driver expects to resume filming in November. Before then, she has one more role lined up before the birth, playing Uma Thurman's best friend in the aptly named indie film Motherhood. When she was offered the role she told writer-director Katherine Dieckmann she was already pregnant. "And she said that was fine – she would just rewrite my role so my character is pregnant."

As for now, she is focused on a short acoustic tour to promote her new album, determined to prove to the sceptics that it is entirely possible to combine music and film careers. Indeed, she has sent out a message to assure her fans of her future plans: "I plan to carry on making music, movies, babies, dinner and stories until I drop."

Minnie Driver plays the Arts Theatre, London WC2 on May 12; 'Seastories' is out on the same day (www.minniedriver.com). In tomorrow's Arts and Books Review: Nick Hasted's caustic take on actresses who think they can sing, from Juliette Lewis to Scarlett Johansson.