SHOULD George Lucas ever need a strong working-class Jedi name, he could do a lot worse than "Gary Lightbody". The Northern Irish Snow Patrol frontman is in London, in a room overlooking Nelson's Column, being famous - and that's a galaxy far, far removed from where he was a few years ago, from what his life could so easily have become. Lightbody's nervous disposition is such, he says, that he could do this interview attached to the ceiling, which sounds appropriate for a Jedi knight. His surname is German, he explains - an anglicised version of Lichtenboden. "In the 17th century, Catherine Lightbody, or Lichtenboden, came to England and we've had roots in Northern Ireland for over 200 years," he says. "It's derived from a nickname - if someone's light-hearted, you know, or light of frame, so hopefully at least one of those is true." The latter, I imagine, is the most accurate: his frame is slight, devoid of flab.

Lightbody's accent has been planed down by his years in Dundee, where he studied English literature in the mid-1990s, and in Glasgow, where he has lived ever since. But his sense of mischief remains intact and he tells a story about his 70-year-old father, who makes mediaeval weaponry and used to send his son to school in a suit of armour. If ever his knees go, he says, he'd like to keep performing in his multimillion-selling band, but as a gigantic mechanical ladybird.

Evidently, Lightbody has a feverish imagination and he can't seem to keep his hands still. He scratches his cheek, his knees, moves his legs up onto his chair, takes them down again. "I am properly, properly insane," he says. "I know that, but sometimes just admitting it to yourself is the first step." He is also - unlike in the past - pretty good company. Because of the way the room is arranged, Lightbody is sitting facing an empty chair with a dictaphone on it and I am looking at him in near-profile from a leather sofa: it feels odd, as if he is talking to somebody else. And sometimes he really is. When the door opens, and a waiter comes in to clear away an unfinished plate of chips and salad, Lightbody tells him to leave the food where it is. "Or I'll break your legs," he shouts. The man looks genuinely startled and begins to withdraw. "I'm only joking," says Lightbody, embarrassed, then whispers: "I'll maybe just give him a Chinese burn."

He runs, he says, on nervous energy, the bulk of which has been channelled directly into Snow Patrol, the band he set up 14 years ago at the age of 18. His commitment to the band, even in the lean years, was total, to the detriment of all else. Splice all his press comments together and you get a picture of an emotionally crippled, self-loathing, self-destructive saboteur - a recovered alcoholic, a man whose reputation for gormlessness in love precedes him - and, of course, a globally successful songwriter. The band, for the most part, has been Lightbody's rock.

The new album is a change from the previous two sonically, but also emotionally. Most of the band's members took music lessons to get themselves in a position to make this album: an ambitious collection of songs that stick in the listener's mind like a splinter. As with the previous two records, Snow Patrol teamed up with Grammy Award-winning Irish producer Garret "Jacknife" Lee (without whom "we wouldn't have been able to find our ass with both hands"), recording the album at Hansa Studios in Berlin and Grouse Lodge in rural Ireland. The result is a happier-sounding Snow Patrol than ever before. Where Final Straw (2003) and Eyes Open (2006) saw Lightbody circling a particular failed relationship with the regret of an animal that has killed the wrong prey, the new songs seem to offer some kind of redemption - or at least a dervish dance on a frozen lake that, we know, could break at any point and consume everyone. He has never revealed who his songs are about (although before the release of Eyes Open he met the person in question to give her a copy of the album and a head start on the album's very personal lyrical content). He won't reveal who the new album is about either, and prefers to stick to generalities.

"People hopefully see that mystery is the key to the whole thing because it means you can superimpose yourself in the songs and live inside them rather than standing outside looking in," he says. "That's what we want for people as a band." It's a good answer, but incomplete. "This album focuses on a relationship I had that completely and utterly changed my way of thinking about life and love, where I didn't feel like being in a band and having a relationship were mutually exclusive as I maybe had in the past."

Lightbody, 32, claims to have only dated five people for any length of time and has problems with certain aspects of romantic relationships. "As liberal and open-minded as I am, part of me is closed off to the idea of real intimacy," he says. "It terrifies me - knowing everything that's going on in somebody's mind and knowing somebody knows what's going on in your mind."

Being in a band, he says, has left him with little to no energy for emotional commitment: his friends in Glasgow, in Northern Ireland - everything and everyone revolves around the band, the band, the band. It sounds like a blatant cop-out. Would things really have been any different had he been working in a regular job? "I get your point," he says. "Maybe the band has given me an easy excuse to not really try. We all should be able to summon up the energy when we fall in love - it's as simple as that. I just think I was malfunctioning more than anything else. I was a robot." He laughs, initiates a Peter Crouch-style robot dance, reconsiders. "I take all the responsibility myself - and so I should, so everyone should. I built up a barrier around myself."

The Lightbody of old, he says, would run headlong in a given direction until hitting a wall, then turn round and do the same again. Like most people's memories of their past selves, Lightbody's are probably unreliable, but his seem particularly gruesome. "I've never intentionally hurt anyone in my life," he says. "I'm not malicious." There have been albums and songs about his infidelities, of course - enough reminders that he is not a saint. And he knows it. "I was a terrible c***," he says. It's a strong word - the wrong word. "Maybe tit' is better," he suggests.

Lightbody looks at his hands, at the ceiling. In what way was he a "tit"? "I was an alcoholic maelstrom," he says, "a chaos magnet. I loathe to think what people that came across me back then thought." Sometimes, still, when he walks around Glasgow, someone will grimace at him with mild revulsion and he will think: "Yup, I was about 25, you would have been about six years younger, yeah ... I understand you." He's not necessarily a delight to be around these days, he adds.

His singularity of purpose is such that you can't split the band from Lightbody - they are the same thing, their fates intertwined, their atoms forever inseparable. The story of how he got from the hole he was in a few years ago to where he is now is a parable worthy of the Book Of Job. When Snow Patrol released their first album, the grungy Songs For Polarbears in 1998, Lightbody was equal parts ego and bolshiness, and certain the record would propel the band to fame. Instead, it tiptoed into the British charts at number 145 and promptly vanished. Its successor, When It's All Over We Still Have To Clean Up (2001), sank without trace. Even before its release, Lightbody was reduced to selling television equipment to support himself. Being dropped by their record label Jeepster shortly afterwards was tantamount to the curtains closing round a coffin. Lightbody's work with Scottish indie supergroup Reindeer Section was "a blip of positivity" in an otherwise awful time. "I was so frustrated by how things were going," he says. "I would take it out on my furniture and my guitars - just smash them up." He would also go on three-day drinking benders, drowning out all but the most persistent reminders of what was becoming increasingly obvious: he had failed.

During this period, two incidents seemed to confirm this impression: Lightbody was beaten up by three men in Glasgow while another man held his girlfriend and watched; then, while out at the Glasgow School Of Art, he crashed down a flight of stairs drunk, ending up sprawled on the floor, barely conscious, his head split open and bleeding. It was, as the album to follow would suggest, the final straw. But from the crack in Lightbody's head something of the "tit" seems to have escaped, while his ego slowly coagulated on the floor. Back home in his Glasgow flat, he began writing Run on a battered acoustic guitar - the band's 2004 breakthrough single and their meal ticket to fame, fortune and a record deal with Fiction/Polydor.

"I think we were maybe hamstrung by the type of person I used to be and allowed to flourish by the type of person I've tried to become since," he says. "I guess I was holding everyone back - sorry, everyone. It's hard for me to look back on those times and even recognise the person I was then. If I sit down and remember who I was when I wrote our first two albums it's unsettling."

As the second single from Final Straw, Run peaked at number five in the UK charts and still seems to encapsulate everything people love or hate about Snow Patrol: it's direct; it's anthemic; it's formulaic; it's wintry; it's brilliant; it's too simplistic. All moot points, of course, if a song sneaks up on you in the right way and chimes like the bells of Notre Dame. "The essence of what we do is melody and honesty," says Lightbody. "That's unchangeable - that's the starting point of everything." After 10 years in the musical wilderness, staring down the barrel of a gun, he is unlikely to see anything wrong with writing big anthemic pop songs for the masses. Chasing Cars, from the album Eyes Open, was the first single by a British band to break the top five in the US since, incredibly, Duran Duran's Ordinary World in 1993, helped considerably on its way by its inclusion in the Grey's Anatomy season finale in 2006. While guitar bands such as Kaiser Chiefs and Bloc Party did cartwheels for the press and scooped industry awards, Snow Patrol quietly sold 4.5 million copies of their album - more than Dire Straits' Brothers In Arms did in 1985, and more than Madonna's True Blue album did in 1986. No wonder Lightbody views the band's struggles philosophically.

"I guess I realise now just how much fate has come to play a big part in our lives," he says. "We needed to get dropped by Jeepster, we needed to make the Reindeer Section records. All these things were a domino effect that led us here, right here to this minute."

Because of his everyman face and body, Lightbody is blessed with an anonymity unimaginable in a Madonna or Mark Knopfler. He says he has been stopped for an autograph in London only once since becoming famous. He is blissfully free to go about his business, fronting a band, selling millions of records. Bar a recent tabloid story that presented the years-old tale about his prodigious drinking habit as if were a continuing problem ("I'm not teetotal," he says. "People can write what they want."), he is rarely troubled by the media at all.

Judging by the imagery on the new album and others, the big problem for Lightbody has always been his need for salvation, by lifeboats, by lights at the end of the tunnel, by anyone or anything. "I spent my life until I was 30 desperately crying out into the void, but just inside my mind," he says. "Some people who know me very well were worried enough about me that they took it upon themselves to just go in there - they sent in a team, a crack squad." Recently, by contrast, he has been able to calm "the madness, the instability, the mood swings and the lack of concentration. I've become more focused, without focusing so hard that I'm like this " (He curls into a tight ball, an intense look of overbearing tension on his face.) Admitting who he was, and who he wanted to be, was key. "Sometimes you can try and block out problems, but you're just pushing them down deeper and they actually manifest themselves physically in bad skin or whatever." He describes himself as a humanist. "It's all about people for me. You have to let people change your world view. You can't be fixed because when something happens outside your world you just deny it and end up like this " (He doesn't curl over again, but the overbearing tension is back on his face).

The most pleasing thing about Lightbody is that he says none of this in an obvious way. He discusses himself mostly in painful prose, his sentences peppered with self-effacing jokes and non-sequiturs. He holds his arms out to show how balanced he has become, or is aspiring to be.

He has a flat in Ireland, eight miles from Belfast (because he has a 15-month-old niece he wants to spend time with) and another in his adoptive home of Glasgow. He is torn between Scotland and Northern Ireland as ideal places to live, he explains, and eventually declares a tie. Unlike the other band members, he is currently single and faces no immediate pressure to settle down - although he may want to one day, one imagines. "It still comes down to the fact I'm never anywhere for very long," he says. "That's a big problem for any new relationship. The girlfriends of the other guys in the band know what to expect - their relationships are established, they can come out and visit us on tour. Trying to start something up now and then saying Right, see you' is not very chivalrous - it doesn't exactly smack of commitment. Then again, you know, maybe I shouldn't read too much into things."

Chivalry? Not reading too much into things? Whatever next for Gary Lightbody? "I'm thinking euthanasia, or if it gets too bad, cyanide," he quips. "As long as I'm the centre of attention."

Snow Patrol's new album A Hundred Million Suns is released by Fiction/Polydor on October 27