The Jonas Brothers were a bone fide band on the brink of modest fame when they agreed to star as a fictional group in the Disney blockbuster, Camp Rock.

But the made-for-TV film, which attracted 24.5 million viewers in the U.S., has lifted the brothers into the stratosphere.

The thousands of squealing girls at this week's British premiere are testimony to the fact that Kevin, 20, Joe, 19, and Nick, 15, are global sensations.

Tween idols: Demi Lovato and Joe Jonas in the film Camp Rock

Not to mention rich, if you consider their own pop-rock album A Little Bit Longer is Number One in the U.S., they have just completed a sell-out world tour and are soon to shoot Camp Rock 2.

Sons of a pastor, these boys are perfect tween pin-ups: no sex, drugs or swearing  -  just rock 'n' roll. They wear 'promise rings' to show they will abstain from sex before marriage.

But for cynics such as comedian Russell Brand, they are an easy target. At Hollywood's MTV Video Music Awards, he revelled in showing the audience a ring as if he had 'won' it from a Jonas brother backstage.

But the Jonas juggernaut is moving so fast and furiously that Brand's insults are water off their backs. 'I think he ran out of material after a while,' says Nick.

Like the Osmonds and Jacksons, the Jonas boys come as a package  -  Joe refused to sign up to Camp Rock unless his brothers were given roles.

The Jonas Brothers (from left to right) Kevin, Joe and Nick arrive for the Disney Channel European premiere of Camp Rock in London this week

So what is the frenzy all about? Camp Rock is a modern Cinderella tale. Mitchie (Demi Lovato), a teenager of modest means, wants to prove herself to Shane Gray, a brattish pop star (Joe Jonas).

Dark-haired and sensitive Joe is the heart-throb of the trio. More intense, curly-haired Nick is the group's songwriter, while the even curlier Kevin is the funny man.

Joe has been described as the Mick Jagger of the Jonas Brothers, but without the womanising, of course, because the selling point of the band is their unimpeachable image.

'We love each other a lot,' says Kevin. 'We weren't jealous when Joe got the part nor when we were in the film but with lesser roles. Instead, Nick and I said: "Great, we're off to play golf, see you later, Joe." '

The boys are co-managed by their father, Kevin Senior, and travel as a family. That includes younger brother

Frankie, seven, who is known as Bonus Jonas after setting up his own band, Hollywood Shakeup.

Nick plays Nate; Joe is Shane Gray; Demi Lovato is Mitchie Torres and Kevin plays Jason in the Disney film Camp Rock

Brought up in Wyckoff, New Jersey, their influence comes from their musically gifted father and their mother Denise, a talented singer.

'I was discovered in a hair salon,' says Nick. 'Someone heard me singing and put me in touch with a manager, who sent me to Broadway.

'I made a solo album, but then my brothers and I wrote some songs together and we took it from there. Dad always told us that the key to success is humility.'

The boys learned this the hard way after Columbia Records dropped them last year, before the Disneyaffiliated Hollywood Records snapped them up.

'Being dropped was a steep learning curve for us,' says Joe. 'Having each other as brothers helped. And having our whole family on the road helps us to retain normality.'

So are the Jonas Brothers and co-star Demi Lovato just a package to provide the latest musical monster?

'We consider ourselves to be a real pop-rock band,' says Kevin. 'We write and play our own songs. We love rock, loud guitars and don't do dance routines. Just because we've not rebelled against our parents does not mean we can't be rock stars.'

They are sensitive on the subject of their promise rings.

'They are a constant reminder to live a life with strong moral values,' he says. 'Chastity is a personal thing and wearing these rings is a private decision we've made. We do date, but it's hard to fit it in with work.'

Despite their gruelling schedule, the boys even found time to write an album for Demi.

'My songs needed a polish, which is where the Jonas Brothers came in  -  and it all began on Camp Rock,' says Demi.

Camp Rock premieres on the Disney Channel on September 19 at 6pm. The soundtrack to the movie is out now on Walt Disney Records.