As ITV's The X Factor continues its search for the next chart superstar, judge Louis Walsh talks to Hannah Stephenson about his spat with Simon Cowell and his friendship with Sharon Osbourne - who walked out of the show on Saturday, upset over the night's eviction. It is hoped she will be back this week.

ON the surface, The X Factor judge Louis Walsh is the lower profile cheeky chap on the show who giggles a lot with Sharon Osbourne, lets down talentless pop wannabees gently and throws the odd tantrum at 'Mr Nasty' Simon Cowell.

But it's not Irish blarney and a genial manner that make a man as influential as Walsh is today in the hugely cut-throat world of the music industry.

Sharon Osbourne warns: "Don't let his charm fool you, because behind all the smiles and laughter, Louis has a tough and ambitious streak."

Meeting him just prior to the start of the The X Factor live shows on ITV1, he looks nothing like a music mogul, neither trendy nor sharp-suited, just jeans, pink shirt and well-worn navy cardigan. Well, at 55, I suppose the cardigan is allowed.

Walsh is instantly likeable, encouraging me to ask him anything, yet after an hour in his company and endless diversions in conversation, I'm not even skimming the surface of what makes him tick.

The pop manager, whose success stories include top acts such as Shayne Ward, Westlife, Boyzone and Girls Aloud, is now encouraging would-be pop stars further by bringing out Louis Walsh's Fast Track To Fame, a guide to how to become a music superstar and the pressures and pitfalls within it.

Critics of The X Factor might wonder how such an affable chap can be happy to watch fame-hungry hopefuls, some as young as 14, make complete fools of themselves in an effort to gain a foothold on the ladder to stardom.

Some of the initial auditions are horribly cringe-making, as cretinous candidates humiliate themselves in front of the cameras. "I can see why people criticise The X Factor," he says. "But all these people queue up outside. We don't make them queue up. We like to show the good, the bad and the ugly.

"We show the viewers what really happens. We could cut out all the awful people and just show the talent, but people wouldn't watch the show for that. People watch it because all human life is there."

Every week viewers see contestants bursting into tears of elation or devastation in equal measure depending on whether they've made the next round. Does he ever consider how the losers (or winners, for that matter) will cope when the cameras stop rolling?

"It doesn't bother me because that's what the music business is like," he says simply. "Only one person can be number one in the charts every week. The rest go and the strongest survive. You have to be tough. It's very stressful on the live show because we all get involved. Sharon and I take it more personally but we try to hide it. You have to be honest."

The show has been so successful, he says, because, "it's voyeurism at its best". Yet he is frustrated with some aspects of the music industry. "I'm disillusioned by the way the music business works, if I'm really honest, because it's not necessarily the most talented people who make it to the top in the real world."

He cites Robbie Williams and The Spice Girls among those who have made it without that much singing talent.

"Robbie is a great showman, but I just don't like his voice. I once said he was a karaoke singer which was probably an unfair statement. But Robbie is living proof that you don't have to have a great voice or be a genuinely talented musician to become a music superstar. I much prefer Gary Barlow."

Walsh was famously sacked from The X Factor in March and then reinstated in June, in what cynics believed was a big publicity stunt. Unsurprisingly, that allegation has been denied by all involved.

It does seem odd, though, that Walsh was willing to jump right back into The X Factor hotseat, given that Cowell, who produces and owns rights to the show, had stabbed him in the back.

Now, Walsh and Cowell have patched up their differences. "He's a really nice man, and much nicer off camera than on camera. We're both entwined. I also work with Simon because my two acts, Westlife and Shayne, are signed with him." (Cowell works in partnership with Sony BMG).

Socially, Walsh meets regularly with Sharon Osbourne. He says: "I totally trust her, she's very honest with me and I've learned an awful lot from her. I've watched what she's done with her family. She's a mother hen. She's glamorous, she looks fantastic and she's a great advert for all that surgery."

The show may have raised his profile but it hasn't changed his life, he says. "I see through it all because I've been there with all the artists. I may be flavour of the month because I'm on a TV show but it hasn't changed my life at all."

Walsh was brought up in Kiltimagh, County Mayo, the second of nine children. While his brothers played football, he escaped into a world of music, listening to Radio Luxembourg. On leaving school he went to Dublin and started out managing show bands and Eurovision Song Contest winners Johnny Logan and Linda Martin, before breaking into the pop world with Boyzone in the 1990s.

He now lives in Dublin for around six months of the year, has an apartment in London and a luxury holiday pad on Miami's trendy South Beach.

The cheeky grin returns when I ask if he has a partner. "Don't go there," he giggles, shaking his head and waving a finger at me as if I've asked him a naughty question, evasive to the last.

"I'm not the marrying kind. I don't want to get married. I'm married to my job," he says.

He's currently in talks with Boyzone to try to get the original band back together next year and, for a man who once said he didn't want a career in TV, The X Factor will be followed by a cameo role in Rock Rivals, a TV drama based on The X Factor, to be screened next year.

"I'm not trying to be a celebrity. I've a small part on a big show," he says.

He smiles mischievously as he gets up to leave, generously inviting me along to one of the The X Factor live shows. But will that give me any more insight into this man who can move pop mountains?

I doubt it.

* Louis Walsh's Fast Track To Fame (Bantam, 16.99).