Eliza Doolittle, summer's pop sensation

Eliza Doolittle is this summer's pop sensation. Her debut album raced to number three in the UK charts, turning the airwaves peachy with its feel-good hooks and recession-defying lyrics: 'Don't need no moneybox/ Cos I've got all I need/ Right here with you, my dear.' A BBC reviewer described her defiantly English singing voice as 'a beautiful, expressive thing, high and clear with an occasional emotive crack.'

And so it should be, for Eliza's mother is Frances Ruffelle, star of musical theatre, and her grandmother is Sylvia Young, founder of the eponymous theatre school. But Eliza, 22, is no polished stage school creation (interestingly, despite her obvious theatricality, Eliza's parents decided not to send her to the alma mater). In person she has a slightly gruff, teenage manner that masks, I think, a thoughtful confidence. And although she has, almost inevitably, been compared to Lily Allen, Eliza has a different appeal.

The stand-out track on her eponymously titled album, which went to number five in the singles chart, was the cheery 'Pack Up' – a riff on the First World War marching song 'Pack Up Your Troubles In Your Old Kit Bag' – which combined Eliza's voice with a brass-soul sample. She reserves a few sharp lyrics for people who spend too much time gelling their hair, and who 'waddle round with Gucci bags', but frankly, she's not much of a satirist. She makes Lily Allen look like Jonathan Swift. Her strongest suit is sunny melodies and cha-cha-chas.

Eliza is a lifelong Londoner who currently lives next door to her mother in Primrose Hill (Ruffelle's pad has Maggi Hambling paintings on the wall and her best friend, Sadie Frost, often pops round for tea). Face-to-face, Eliza has the dewy complexion of a milkmaid, all creamy dimples and Tess D'Urberville tresses. She has a beauty spot, perfectly placed by nature on her right cheek. She is wearing her trademark mini shorts and box-fresh high-top trainers (Nike Royalty Macaroons in baby blue, to be precise). She has 'about 25' pairs, most of them presents from Nike, strewn across her bedroom. She gets through her busy new popstar routine on coffee, which she has only just started drinking, as well as echinacea, vitamin C and iron. I had been wondering if her lyrics 'Oh Mr Medicine/I need my vitamins/Will I feel better then?' might be a code for something naughtier. 'No, it's not about drugs,' she laughs. 'I take vitamins because I don't eat a lot of protein as I'm vegetarian.' Nut roast and Nando's vegetarian pittas are on her blog list of her most favourite things in the world, along with 'old libraries' and 'Aslan'.

Her real name is Eliza Caird, her father being the renowned RSC director John Caird. Her parents met when Caird was co-directing (with Trevor Nunn) Ruffelle in Les Miserables. Ruffelle was 22, and won a Tony award for her role as Eponine. Caird was 17 years her senior and married. Not long after his wife, Ann, gave birth to their son, Samuel, Caird left to move in with Rufelle, who had fallen pregnant with Eliza. The couple had another child – a son, Nathaniel, and got married in 1990, separating three years later (Frances's pregnancy, announced, as it was, a week after she won the Tony Award, was a great shock to Trevor Nunn and subsequently the show's producer, Cameron Mackintosh, never worked with her again).

'My dad's really well spoken and my mum's from the East End, so when they were together people used to call them Eliza Doolittle and Henry Higgins. (Eliza's voice hovers comfortably between the two: half rain in Spain, half Cockney flower girl.) So that's where she got her stage name? 'Doolittle was also my nickname sometimes.' She wasn't exactly a proactive child, I take it? I was always looking out of the window at school, wanting to be somewhere else.' She went to Channing, the private London girls' day school, then to the progressive Hampshire public school Bedales. 'A lovely school, but I really missed London and my friends. I left after GCSEs. I thought it was just dumb being there.' Was she there at the same time as Lily Allen? 'No, after. And he got expelled.' She adds, proudly, 'I didn't.'

The year after Ruffelle and Caird separated, Ruffelle finished tenth in the Eurovision Song Contest, where she met Virgin Records executive Rob Manley. They had a son, Felix, now 15, but split up in 1997. Frances is now in a relationship with businessman James Day, 30, the founder of Urban Golf, a chain of clubs featuring computerised golf simulators. So Eliza's family comprises a complicated but close set of step-siblings – two older brothers and an older sister, and three younger brothers and two younger sisters. 'They're mainly all my dad's, except one brother is my mum's with another boyfriend. There are lots of different wives, boyfriends and husbands.' Quite bohemian? 'Kinda. Not like the Primrose Hill set though.' Did it feel crowded? 'No, I loved it. It's all good. It's never been distressing. I would hate it if I didn't have my brothers and sisters, so I'm,' she shrugs sweetly, 'thankful for my mum and dad splitting up.'

Eliza, meanwhile, has a longstanding boyfriend, Ollie, whom she has known since she was 12. 'We were friends before and then one of those things. It just happened.' They had their first kiss to a Steely Dan track, 'Home At Last'. What does Ollie do? 'He's actually just figuring that out at the moment.' Does she envisage herself having a conventional married life? 'There's a part of me that wants to be certain about getting married because I've seen so many break up and there's a part of me that wants to not get married because it's so uncertain. And a part of me that thinks it's really nice to have a day to celebrate your love I don't know, but I can't see myself becoming a conservative person with big house, two kids and a dog.'

It is not surprising, considering her complicated family arrangements, that Eliza does not foresee a traditional future for herself. But a constant in her life has always been her grandmother, Sylvia Young, one of the best-loved figures in British showbusiness, who has helped guide the careers of, among others, Amy Winehouse, Nicholas Hoult and Billy Piper. 'My nana is like a grandmother to hundreds of kids,' says Eliza. 'But obviously I'm the luckiest because I get to hang out with her the most. I saw her yesterday actually. She's disciplined with school stuff of course but everyone knows she's one of the loveliest ladies in the world. She used to spoil me so much. She would never say no. We used to go and get sweets at Woolworths and do all the things my mum wouldn't let me do. She's always telling me I should be wearing a coat, that I'm going to catch a cold.' As well Grandma might, given those shorts.

Eliza wasn't allowed to go to Sylvia Young's Theatre School. 'I always wanted to! But I just trusted that it was the right thing not to,' she says, diplomatically. 'My parents wanted me to have other opportunities, to become a doctor or an artist or whatever I wanted to be and they thought that with theatre in my family already, going to the school as well would be too much pressure.' Her father directed the RSC's landmark Nicholas Nickleby as well as countless other productions. Was she ever involved in any of his shows such as, say, Les Miserables? She's a spit for the brat on the poster. Did she play Cosette? 'I did, actually!' she says, faintly embarrassed. 'I owe that show a lot I was eight years old and I was in the theatre when the auditions were on and I said, "Please can I audition as well?" My dad didn't want me to so the fact that they picked me meant they must have liked me for some other reason.' She only appeared once a week in Les Miserables, for a few months, but it taught her that she didn't want to do something as repetitive as musical theatre. 'I like doing different things all the time – recording, performing, writing.' Moreover, she was sent to bed before the curtain call. 'Didn't even get to take a bow!'