EVER since Elvis was unleashed on an unsuspecting world, millions of teenagers have worshipped a teen idol. Wil Marlow looks back over 40 years of Donny, Tiffany and Gareth

THIS year Will Young and Gareth Gates have reigned supreme as the Princes of Pop. Ever since they captured the hearts of teenage pop fans across the country, competing against each other in TV talent search Pop Idol, the two singers have been loved by an adoring fan base.

To promote his debut album, What My Heart Wants To Say, Gareth Gates appeared at a Virgin Megastore in Glasgow this week to sign copies of his CD. More than 600 fans turned up to meet the star, some of whom had queued for hours just to get a glimpse of him.

Elizabeth Singer, aged 14, had travelled from Aberdeen with her mum so she could meet her idol as a birthday treat. Before she met him, she said: "I don't know what I'll tell him. I suppose I'll say I love him."

The passionately chaste love affair between pop star and teenager is nothing new. Young and Gates are merely fulfil a role that was created by Elvis Presley and The Beatles five decades ago. Ever since Elvis first shook those hips, the teenager has fallen head over heels in love with the pop idol of their choice.

A new book, Behind The music: Teen Idols, by Sarah Kelly, looks at the many objects of desire that have made teenagers across the generations swoon in delight.

"If you love music, chances are you've worshipped your share of pop stars when you were a kid," says Kelly.

"It was about a certain time in your life. A time of figuring out what you liked and what you didn't. A time when there was pure, clean excitement in having discovered something new, like a song, and being allowed to just love it."

It's quite apt that Gareth Gates recently covered the Elvis classic Suspicious Minds -- the nation's current teen idol paying tribute to the very first one.

With Elvis came rock'n'roll, the music that teenagers immediately latched on to as it was everything their "clueless" parents didn't like.

Then, in the 60s, mass hysteria followed four musicians from Liverpool. The Beatles caused such hysterical screaming from their female fans that even looking at the footage now, you are overwhelmed by their loss of control.

For teenagers, worshipping a pop idol was, and still is, about asserting individuality in the face of the parents' upbringing.

"Teen adoration is undiscerning," says Kelly. "Once an artist is on top it hardly seems important to the fan how they got there. Whether they have musical credibility or not isn't important. They are defined solely by their audience."

David Cassidy is a prime example. Starring in The Partridge Family for four years made the singer a huge star across the world.

"It happened so quickly, and I remember thinking it was just a job," says Cassidy. "I thought, 'Well, that's cool, I've got another month's rent done'." The fans picked Cassidy -- he didn't pick them. And because of that, he became the first proper teen idol. Elvis and The Beatles are remembered for their music more than the adoration they generated, but it's Cassidy's smile that still lingers in the minds of his fans.

Boy singers like Donny Osmond and Leif Garrett would later set in stone the teen idol rules that Cassidy had accidentally created, the rules that Gareth Gates is now following so carefully.

They were young, good-looking, they could sing, dance and make girls faint by batting an eyelid. That formula became big business and the singers soon became commodities that could sell anything with their picture on it.

But teenage girls were starting to want more from their idols. They didn't just want someone to lust after, they wanted someone to look up to.

Debbie Gibson and Tiffany were the Britney and Christina of their day -- Gibson the squeaky clean all-American singer, Tiffany the more sultry, fun one -- each a hero to their adoring female fans.

In the 90s, teenagers around the world were spoilt for choice, but their feelings for the likes of Take That and the Spice Girls were as strong as any David Cassidy fan.

"It's never-ending," says Kelly. "Just when you think it's over, the pop star cookie cutter offers up another girl singer to expose her midriff, or a group of boys to perform great dance moves.

"As long as teenage consumers have the money to spend, the carbon keeps on making copies."

Behind The Music: Teen Idols, by Sarah Kelly, is out now, priced £7.99.