No sex, no drugs, just rock n' roll: Are the Jonas Brothers the world's cleanest cut band?

As a contender for the title of teen pop sensation, it is hard to imagine a more unlikely group – three sons of an American pastor who don't drink, smoke or swear, and have vowed not to have sex before marriage.

But judging by the screams greeting the Jonas Brothers in London yesterday, our tweenage girls don't mind their idols a little strait-laced.

The brothers, who all wear silver 'purity rings' to mark their determination to remain virgins until marriage, were greeted by a crowd of 1,000 school-age fans outside Royal Festival Hall.

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Three of a kind: The Jonas Brothers, from left, Kevin, Joe and Nick, hold court in London

Jostling and squealing, the girls strained to catch a glimpse of the trio at the British premiere of their film, Camp Rock.

You could almost taste the hysteria: every face was painted, every arm held out a mobile phone to capture the moment, and every heart carried a secret prayer of desire.

The most ardent fans talk about having OJD – Obsessive Jonas Disorder – and it was very much in evidence yesterday.

This JoBroMania is more than just enthusiasm for another boyband. It is the most curious phenomenon in popular culture: the deliberate selling of rock'n'roll without sex or drugs.

The brothers – Kevin, 20, Joe, 19, and Nick, 15 – play their own instruments and write their songs, but are perhaps best understood as a modern-day cross between the Osmonds and the Monkees.

Like the Osmonds, their clean-living values and religious background appeal to parents, while like the Monkees, they are backed by a PR machine that ruthlessly controls their image.

No wonder Russell Brand found them such an irresistible target at the MTV video music awards on Sunday night in Los Angeles.

While hosting the awards, the British comedian produced a ring on stage and implied, with showstopping poor taste, that he had taken the virginity of the youngest Jonas brother.

'Nick was a bit reluctant at first,' joked Brand, 'but after a bit he realised that it was for the best.'

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The comedian was reprimanded by American Idol winner and fellow purity ring wearer Jordin Sparks, who said: 'It's not bad to wear a promise ring because not everybody, guy or girl, wants to be a slut!'

Brand made an apology, which the brothers accepted.

The Jonas Brothers can afford to be generous because they are surfing on a squeaky clean wave, following where the tweenage sensations High School Musical and Hannah Montana have led.

It is no coincidence that Disney own all three blockbusting properties. Executives there have realised there is a mass market ripe for the picking – and untold riches.

The Jonas Brothers are said to have made £7million in the past year alone, releasing two multi-platinum albums and a record-breaking string of hit singles.

So who are they, and what are the secrets of their success? Kevin, Joe and Nick grew up in Wycoff, New Jersey, where their father, Kevin Jonas Snr, was an evangelical pastor and their mother, Denise, a sign-language teacher.

There is also a younger brother, Frankie, seven, who is not part of the band but is rather sweetly known as 'bonus Jonas'.

The band came into being when Nick was discovered singing in a barber shop at six and sent to a talent agent. By the age of seven, he was performing on Broadway.

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He had a solo career, releasing a single co-written with his father and a 'spiritual' album in 2005.

Subsequently, the three eldest brothers decided to team up and release an album through Columbia Records in 2007. It was not a success and the label dropped them.

But this being a Disney story, a happy ending wasn't far away. The brothers were soon picked up by Hollywood Records, part of the Disney empire, and have not looked back since.

After appearing in a guest slot on Hannah Montana they released an album which sold 1.4million copies, followed by a sequel which has sold more than a million so far.

A source at their label says: 'Their clean-cut image is something that parents like and the feedback which we have from teen magazines here is that the teenagers like it too. They are very wholesome and that does appeal.'

There are the inevitable nay-sayers. James McMahon, features editor of rock magazine NME, has described the group as 'sinister and really creepy' and says the UK is 'too obsessed with sex for Jonas Brothers to be really popular'.

With respect, Mr McMahon, the thousand girls screaming on the South Bank yesterday suggest otherwise.

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