From nowhere to Number One: Why Kate Nash is the sound of the summer

On a rare sunny Sunday in June, the artist area at the 02 Wireless Festival in Hyde Park is full of skinny boys in skinny jeans. Outside Portakabins emblazoned with the unimaginative names of their bands – The Cribs, The Rakes, The Twang, The Films, The Heights, The Crimea – they smoke, looking raffish and bored.

In this company, Kate Nash stands out. Wearing a charity shop set of flowery culottes, of the type worn by eccentric bridge-playing aunts, and bright orange tights, she is dancing around outside her changing room. "Come on!" she squeals to her press officer in the Norf London tones of her hometown, Harrow. "Let's go and meet some famous people!"

"But Kate," says the PR. "You're famous."

She is now. Nash, who last week turned 20, has emerged from nowhere this summer to become the hottest thing in pop. At the time of writing, her single, "Foundations", sits at number one in the iTunes chart. Her gigs are packed to the rafters. Magazines in Britain and America are calling to book her for cover shoots. And all this without an album in the shops – though the release of her as-yet-untitled debut has just been hurried forward to 6 August.

How has she achieved this? Well, firstly, Nash makes lovable music. Her witty low-fi songs chronicle her late-teenage life in Harrow – a litany of stupid boys and nights on the piss – to a backdrop of jaunty piano and guitar. At an early Nash gig, I caught the man in front of me laughing and dancing at the same time, during this line in "Foundations": "You said I must eat so many lemons / 'Cos I am so bitter / I said I'd rather be with your friends, mate/ 'Cos they are much fitter." Not many artists can elicit that kind of reaction.

Secondly – as a day spent basking in the reflective glow of her culottes would prove – she is great fun. A representative from Swarovski collars Nash and asks her whether she would like to choose some Swarovski jewellery from the cabinet in the VIP area to wear on stage. "Really?" asks Nash. "Anything?" The Swarovski representative nods her head, thinking, perhaps, that Nash will take one delicate piece from the collection. Five minutes later, Nash strolls out of the VIP tent with so much jewellery she can hardly carry it all. "Ha!" she says, "look at what they gave me!"

Being in demand is a new phenomenon for Nash, and she is determined to make the most of it. Nash had attended the BRIT school in Croydon, whose alumni include Amy Winehouse, and had always wanted to be an actor. But when she left school last year with a BTEC in theatre, no drama colleges would take her, and she embarked on a gap year of odd jobs.

"I was really annoyed," she says. "My Mum – a nurse – had always been one of those Mums who said, 'If you don't work hard, you're going to end up working in Safeways', blah, blah, blah... But I did work hard at school, and I ended up working in these shit jobs anyway."

Her last regular job was in the clothes shop River Island. It was while working there that she did her first gig, on 13 April 2006. Why the change from acting to music? "I'd reassessed my situation," she says. "I'd always wanted to do a gig, and always written songs. So I just booked one and did it. And I got paid. I couldn't believe it. When that first 30 quid went into my hand, I said, 'I'm never going back to River Island'. I did the gig on a Friday, and quit on Monday."

River Island's loss was pop's gain. Within months, Nash had played all manner of odd gigs, built a following on Myspace, and caught the attention of managers and labels. The attention was, initially, too much for her. "I didn't go into gigging so I could get signed," says Nash. "I didn't really know what being 'signed' meant at first. But everyone kept talking about it. There was a time when the thought of getting signed made me want to burst into tears – I just wasn't ready for it. But then, when it happened, I was ready for it, and it's been really good."

Nash has now almost finished cutting her album with esteemed producer Paul Epworth – a process she describes as "stressful; one minute you think it's all shit, the next you think it's brilliant." She met Epworth early in her gigging career, and the pair have formed a solid, if occasionally fraught, working relationship.

If you believe her press cuttings, Nash's big break came when Lily Allen – to whom Nash is sometimes compared – began to champion her young rival. This is half true. Allen was impressed with Nash, and she did make her one of her "Top 8" friends on Myspace. But how important was her patronage? "It definitely helped," says Nash. "She has such a spotlight, and she brought that spotlight on to me."

Nash feels, though, that a lazy, and male-dominated industry has already pigeon-holed her. "I've been boxed as the next Lily Allen because I'm a girl," she says. "We don't sound anything like each other. In fact, they bunch a box of us [young artists] together and call us the new Lily Allens."

Nash has a gripe, too, about being part of the so-called "Myspace Generation". "Some days, I wish someone would just hack into Myspace and destroy it," she says. "But it's a tool of our generation – a way of getting music to people. I didn't have to release any music, or know anyone in the industry, for people in America to hear my songs. That's because of Myspace.

"It's annoying, though, when people write about Myspace like it's the most important thing," she continues. "It's not as important as people coming to your gigs. It's not as important as what I did – taking flyers and demos everywhere I went, and going up to people on the street, and saying, 'Listen to this!' At some point, you've got to make the transition from people listening to you on the internet at home, and people actually coming to see you. You need hands-on stuff to do that."

The hands-on stuff has worked. As Nash's van pulls up at the Hyde Park marquis where she is due to perform at 5pm, she gasps. There are dozens of punters who have been unable to crowd into the venue. "I wish my Mum could see this," she says. "But she's working today." To calm her nerves, Nash launches into a series of cartwheels on the lawn at the back of the venue with her guitarist, Jay Malhotra.

The gig itself is extraordinary. From the back of the tent, maybe 4,000 sweaty youngsters have crowded in. Some have brought placards – one reads, "You Make Me Merry Happy", a reference to an as-yet unreleased number. Outside the venue, punters spill out on all sides – and beyond, there is no one. Everyone is here. Indeed, two enterprising young women, desperate to get in, have unpicked the back of the marquis and sneaked under the mixing desk.

Nash gives a good account of herself, rattling through half an hour's worth of favourites – "Foundations", "Merry Happy" and "Birds", amongst others. But she looks in shock. "Oh my God, I really didn't expect this many people to be here," she says, and you know she means it. She sees some old friends in the crowd, and waves at them, before remembering she is in the middle of a set, and returning to the piano.

As she sweeps some auburn hair away from her eyes, and fixes one of the safety pins holding together her outfit, it becomes clear just how big Kate Nash could become. Not only is she a musician capable of holding thousands rapt in her odd, quixotic musings, she could be a style icon too. That's an odd thing to say about a woman wearing culottes, but it's true. Nash pulls off the quirky vintage look with aplomb.

After she has left her screaming devotees, and signed countless T-shirts and festival passes at the backstage entrance, I ask Nash about her clothes. Where do they come from? "Oh, charity shops, vintage shops," she says. And is there anyone's look you are trying to channel? Nash glances down at herself and breaks out into peals of giggles. "I don't know," she says. "A five-year-old?"

"I used to wear tracksuit bottoms or denim skirts or whatever," she continues, once she has stopped laughing. "I'm from Harrow. I can't deny that I was a bit of a chav. But when I was 16, 17, I got into vintage dresses. I loved Marilyn Monroe. I liked being a bit more theatrical. I like wearing dresses because I've got hips and curves and they suit my figure. A lot of girls get stuck wearing jeans. I like being girly."

Nash may like being girly, but she's not so sure about being a star. After her set, which, by the time we arrive back in the artist area, is already being talked about as a "festival highlight", all she wants to do is "get really drunk". But she still has engagements. First, the press photo call where, in front of 10 agency photographers screaming her name, she has to stand and look pretty. She turns away from the photographers, embarrassed. It's clear she hates every second of their attention. Why? Doesn't she like the way she looks?

"Oh, I feel fine about the way I look," she says. "It's just really weird for 10 people you've never met to be shouting your name and flashing their cameras at you. I'm not Beyoncé." Will she ever feel like Beyoncé? "I hope not. I'm just not that kind of girl. Look at my nails [she displays her unloved nails], look at my fake tan [she points at her milk-white, freckly skin]. I'm an English rose, I suppose. A clumsy English rose."

A second photo shoot awaits. This time it's with the renowned photographer Mick Rock, and Nash is excited. "Mick Rock – I can't believe it!" Before her date with glossy immortality, Nash goes with her pals to the artist canteen, loads up her plate with 14 types of international cuisine, and scoffs the lot. It's hard to imagine Kate Moss doing that before a shoot, but, as Nash would say, "I'm not Kate Moss."

No, she's Kate Nash. She eats, wears and drinks what she likes. When she arrives for the shoot with Rock, she laughs at herself and cracks jokes with Malhotra and Elliot Andrews, her drummer. The photographer, meanwhile, is smitten with her for the same reason everyone else is – she's genuine. Will this quality make it hard for her in the music industry?

"No – I can smell a bullshitter a mile off," she says. "You do meet people [in music] who want to be your friend just because... but you can tell immediately. My real friends have been there the whole time, through good and bad. As I meet people, I'm going to have to judge them, but my Mum brought me up well enough to know who's bullshitting and who's for real.

"I don't go looking for that kind of attention anyway," she continues. "I'm a normal, 19-year-old girl. I'm not going to celebrity parties, and I'm not going to famous nightclubs to hang out with famous people. Sometimes, I might bring my friends along to one of those things just for the fun of it – for a laugh – but that's it. I'm not cool at all. I'm wearing culottes, for God's sake!"

With that, she delves into her drinks cabinet, and pours us two Courvoisier and Sprites, a cocktail which tastes as good as it sounds. Then she says goodbye, grabs the brandy bottle, and disappears with her friends and band mates to the main stage to watch the Kaiser Chiefs. It's exactly the sort of thing a normal, 19-year-old girl might do.

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