She’s a gobby bitch who has a vulnerable side, she’s witty but some find her crass, she’s utterly insufferable and yet fans think her quite lovable. Lily Allen is one of the biggest new stars of the year, a 21-year-old pop singer who has become the sound of the summer — whether you like it or not.

Discovered on the internet, with her single Smile at No 1 and her new album expected to soar up the charts tomorrow, Allen is already attracting doom-laden headlines about a cocaine habit that she denies, with the qualification that she admits first taking drugs at 13, dealing ecstasy at 15 and checking into the Priory at 18.

Still, girls gotta have fun and she is also partial to the odd drink, sometimes when performing. A journalist recalls going to interview her at her record company earlier this year: “I went into a publicist’s office and she emerged from under a desk where she had been asleep. She had gone to bed at 5am and was very hung over.”

This sort of thing is music to the ears of thousands of teenage girls who yearn to have the smarts of their heroine. To Allen’s credit, her actual music is highly rated.

She spurns the transatlantic wailing beloved of many British girl singers in favour of a vocal style described as “angel-sweet and hard-arse tart”.

She performs her own lyrics in the sharp style of Ian Dury to the sounds of ska, reggae and hip-hop. Funny and upbeat, her album Alright, Still is a scabrous take on a girl’s life in the city.

With jolie-laide looks that evoke a younger version of the actress Kathy Burke, Allen recently expressed a refreshing penchant for “really tall or really fat” men such as the beanpole footballer Peter Crouch and the tubby disc jockey Chris Moyles.

This might have had something to do with the fact that her boyfriend, the A&R man Seb Chew, has just dumped her. By serendipity, her record Smile expresses vengeful joy at an ex-boyfriend’s unhappiness. How neat is that? Yet her street cred is constantly undermined by reminders of her middle-class background in Islington, north London. It galls her: “Everyone thinks that because my dad appeared in a few B-movies and wrote some shit football song, that I’ve been driving around in limos all my life. It wasn’t like that.”

Her long-suffering papa is, in fact, the actor and comedian Keith Allen, whose credits extend beyond B-movies. He appeared in the film Shallow Grave, won critical acclaim in a BBC adaptation of Martin Chuzzlewit, and is a member of the band Fat Les, for whom he wrote the 1998 song Vindaloo and other football anthems.

His daughter has not forgiven him for leaving her mother, Alison Owen, when she was four. Owen is now a film producer, but then she was a production assistant and life was tough.

“I spent the first nine years of my life in a council flat eating spaghetti on toast. My mum would be on the phone begging my dad for money,” Allen said. “So, yeah, my mum knew Anthony Minghella. We’d sit there at a premiere with Gwyneth Paltrow. Mum’d get paid to do one job, but it had to last a long time: mortgage, tax and three kids’ school fees.”

She even claimed that her father was a hindrance to her career: “I had doors slammed in my face from lots of [record] labels. It was because I was going out every weekend getting pissed and because I was my dad’s daughter — that worked against me.” This is a curious claim, since she has admitted that his influence helped her to secure her first record contract.

However, she has a curt message for those who accuse her of nepotism on her website: “All haters simply f*** off! Losers! I’ve got better things to do with my time than respond to all the pathetic wankers dissin’ me.”