Neil McCormick wanted - no, intended - to be a rock 'n' roll megastar. There was only one problem: a classmate nicknamed Bono Vox got there first. He describes his forlorn existence as Bono's doppelgänger

BONO stole my life.

As a teenage dreamer attending Mount Temple School in Dublin in the Seventies, I had my whole future worked out in careful detail.

I would form a rock band, make a series of epoch-shifting albums, play technologically mindblowing concerts in the biggest stadiums on the planet until I was universally acknowledged as the most famous man of my times and I would indulge in all manner of secondary fantasies along the way: make films, break hearts, befriend my idols ... oh, and promote world peace, feed the poor and save the planet while I was at it.

There was, as it turned out, only one thing I hadn't counted on. A boy sitting on the other side of the classroom had a few plans of his own.

I went to school with Paul Hewson, a fellow gawky teenage rock fan who answered to the frankly rather ridiculous nickname Bono Vox. You may have heard of him. Bono is a big star these days but, the truth is, he was always a bit of a star, even in the limited environs of the school corridor. Everyone knew Bono, with his pugnacious physicality, restless energy, mischievous humour and all-inclusive grin. I think of him in Mount Temple as a gregarious charmer, loping about the place like a stray dog, sniffing out interesting conversations and activities, making sure he was part of whatever was going on.

His ascent to real stardom began on Saturday, August 25th 1976, when he attended a meeting in the kitchen of a house in Artane convened by a fellow pupil, Larry Mullen, who wanted to form a band. The reason I am so sure of the date is because my younger brother Ivan was there, and made the legendary entry in his diary: Watched TV. Joined a pop group with friends. Had a rehearsal. Great. Sadly, it is not a matter of record exactly what he watched on TV. Such is the fickle nature of teenage diaries.

This was the first gathering of a band who would go on to conquer the world, once they had dispensed with my brother's services (he lasted three rehearsals). A band called ... well, Feedback actually. There would be a few name changes before they became U2. They were briefly The Hype and even more briefly The Larry Mullen Band. Indeed, for a while they considered calling themselves The Blazers, a name sensibly discounted on the prosaic basis that Mount Temple did not have a school uniform.

I vividly recall Feedback's first gig, on four tables held together by sticky tape in the school gymnasium. Bono stood centre stage at his microphone, guitar slung around his neck, looking defiantly over the boisterous crowd of kids. Guitarist Dave Evans and bassist Adam Clayton stood either side of him. Drummer Larry clicked his sticks together and the group launched into a coarse, speeded-up version of pretty boy rock star Peter Frampton's Show Me the Way, kicking off with a roaring D chord that sent a shockwave through the room.

With the wisdom of hindsight, I know this début must have been a fairly dubious affair. There was nothing remotely cool about their selection of songs, for a start. They played, of all things, the Bay City Rollers' pop anthem Bye Bye Baby and a Beach Boys medley. They had no soundcheck, no experience, nothing to go on but hope and desire. But when Bono stomped across the shaky stage, grabbing his microphone stand, yelling "I want you ... show me the way!", the little girls from the junior classes started screaming. You could say I was impressed.

It wasn't long before I had a band of my own, formed with my brother Ivan and another teenage malcontent, Frank Kearns. We went by the name Frankie Corpse and the Undertakers. Well, it was 1977. We played a lot of gigs with the nascent U2, in the school disco (returning next morning to dutifully clean up the mess we had made) and in places like Howth Community Centre (with Larry sitting in when our own drummer, the aptly named Keith Karkus, was detained by police for unspecified punk rock atrocities) and McGonagles.

I loved U2 then, and I love them now. I watched them coalesce from a frankly rather terrible covers band (I will never forget the spectacle of them playing a version of a popular TV theme tune in the school common room, with Bono punctuating the instrumental blues riff by leaping into the air at appropriate moments to shout "Batman!") into a white hot rock group, with sweat dripping off the walls of Dublin clubs, the Edge's echo-driven guitar splitting and separating into a chiming wall of harmonics, while Bono urged us on with a passion bordering on belligerence.

Those were my Beatles-in-the-Cavern moments. A lot of people in Ireland feel that U2 belong to them. And they do. But I was there from the very beginning, before anyone had any idea what it might amount to.

Including me. Sure, I thought U2 were good . but I thought my own bands were better! As the singer in a succession of outfits with names like The Modulators, Yeah! Yeah! and Shook Up!, I went through a lot of haircuts and fashion makeovers, always with my eye focussed on the main prize. And I came close. Well, close to getting signed by a record company. WEA offered Shook Up! a deal after our first show in London. They told us we could be bigger than The Police or Duran Duran. Then they dropped us unceremoniously on the grounds that the MD thought the singer's hair was too short. My bandmates were supportive, but I didn't go back to a hairdresser for more than five years.

While my friends in U2 ascended to the stars, I found myself mired in the underbelly of the music business. By the time they were playing Wembley stadium, and I was still worried about whether enough people would turn up to our gig at Wembley Coach and Horses, the penny finally dropped. It was time for me to give up. Of course, this was several years after the music business had given up on me.

I became that journalistic cliché: failed rock star turned rock critic. One day I was sitting in my shabby, unheated excuse for an office above a bookies in London, watching rain drizzle down a dirty window, when Bono phoned from Miami to tell me about smoking cigars with presidents and singing duets with Frank Sinatra. I was in no mood to listen.

"The problem with knowing you is that you've done everything I ever wanted to do," I complained. "I feel like you've lived my life." "I'm your doppelgänger," Bono replied. "If you want your life back, you'll have to kill me."

And in that throwaway remark was the germ of a book I would one day write about living in the shadow of superstardom. "You're not the only one of my friends who complains about how hard it is knowing me," Bono has admitted.

People think it must be great being pals with a superstar. And there are some benefits. You get access to the VIP section, where bouncers discreetly usher you beyond the red cordon to a magical place where tables are laden with champagne and whiskey, supermodels laugh at your jokes, film stars recite poetry in your ear, and someone else always picks up the bill. The downside is that every time you have flown First Class it's just that little bit harder to go back to Economy.

And there is always something to remind you that you are only in this exclusive world as a guest, not an inhabitant. Like the time Bono, David Bowie, Brian Eno and I had our picture taken together at a concert, only for it to appear in the newspaper the next day carefully cropped around Bono's shoulder to cut me out.

Or the time we went to the Pope's house in the Alban Hills. Now, that is a big house. The Biblical expression "in my father's house there are many mansions" barely does it justice. You could fit entire streets in single rooms. Our small entourage was led from one vast chamber to another until we arrived at the Pontiff's quarters. But when we approached the door, a glorified bouncer dressed in the medieval costume of the Vatican Swiss Guard insisted I wait outside.

This was the story of my life with Bono. I never had quite the right pass or sufficient kudos to gain access to the final sanctum. "Just don't tell them I'm not a Catholic," Bono whispered to me as he was led inside by the Swiss Guard.

Oh, I've had some high times in Bono's company, moments when I glimpsed the dark appeal of being part of the entourage, like Elvis's mafia, enjoying glamour by association. I could tell you about the time I rode in a minibus over San Francisco's Golden Gate Bridge with Bono, The Edge and Noel and Liam Gallagher from Oasis. U2's One came on the radio and everyone started singing, the biggest rock superstars in the world delivering an impromptu rendition of a song of brotherly love. "We are one," they sang, "but we're not the same, we've got to carry each other, carry each other ..."

And I sang too. But, whatever it says in the song's lyrics, we are not one. While my own musical career crashed and burned, Bono's star swelled to such a magnitude that somewhere in the darkest recesses of my psyche, I felt as if I were being eclipsed.

Bono became inescapable. Walk into a shop and there he was, blasting over the in-store stereo. Turn on the TV and there he was, shaking hands with presidents and prime ministers. When your friend has achieved everything you ever wanted, how does that reflect on your own life? The small triumphs of ordinary existence can disappear in the blinding spotlight of superstardom.

The worst thing for me was that Bono became a kind of archetype who invaded my dreams nightly, a subconscious reminder of my own sense of failure. I would be standing on a stage in front of tens of thousands of people, with my band behind me, only to slowly realise the band was U2 and I didn't know the words to any of the songs. Frozen with embarrassment, I would be gently pushed aside by Bono as he assumed his place at centre stage.

I complained about this to him one day. "I don't want you in my dreams!" I complained. "They're private!" "I'll try to remember that next time I'm wandering about at night looking for somebody's head to get into," laughed Bono.

So I wrote a book about all of this, which, as it happens, Bono loves. "I was Neil McCormick's fan in school," he wrote in the foreward. "He was much cooler than me, a much better writer and I thought he'd make a much better rock star. I was wrong on one count." Bastard.

• I Was Bono's Doppelgänger is published by Penguin (www.bonosdoppelganger.com) and is reviewed in tomorrow's Books pages. After 25 years of heartbreak, on September 27th Neil McCormick will release his début solo album, Mortal Coil, under his musical alias The Ghost Who Walks (www.theghostwhowalks.com). He doesn't expect it to sell quite as much as the forthcoming U2 album, but hope does spring eternal