it's a sweaty night just before last Christmas. The Theatre Royal, Drury Lane, has turned its stage over to a pop group, and is now paying the price in the form of major structural damage. The frenzied stomping of adolescent girl-feet has cracked the balcony, and security men with walkie-talkies are taking the back stairs three at a time in a vain bid to stop the encore - "Get the band off, for God's sake, the whole building's coming down!"

Nine months later, at a National Film Theatre screening of Kes, Ken Loach's landmark of gritty social-realist pathos, the air is sweetened by a heady hormonal dust-cloud. The tall, quiet, bespectacled man who has come to introduce the film is the epicentre of another little teenage earthquake. The name of this man - the singer of the group who will not be asked back to Drury Lane in a hurry - is Jarvis Cocker. He is now sitting in a chair opposite me, eating a piece of bread and butter; his long legs painstakingly arranged before him in the style of a giraffe bending down to take the best leaves off a shrub.

The words of his band Pulp's new single Mis-shapes are ringing in my head, because I was listening to them on the way to the interview, and because they are the sort of words that do ring in your head. "Mis-shapes, mistakes, misfits, raised on a diet of broken biscuits" - Jarvis' nasal Sheffield tones summon his underdog congregation for a gleeful hymn. "We're making a move, we're making it now, we're coming out of the sidelines... We won't use guns, we won't use bombs, we'll use the one thing we've got more of - that's our minds!"

Jarvis Cocker has the precious gift of being ironic and sincere at the same time. His group's rapid ascent to the A-list after years of thankless struggle has not left him unmoved. "If you do something that you believe is good for a long time - as we did for 12 years without anybody taking any notice - it does make you feel like maybe there's something wrong with you. So when you do get some acceptance, you breathe a sigh of relief". It must be strange, though, when so much of the point of Pulp seems to be not being accepted. "But I never wanted to be different", Jarvis insists, "I wanted to be the same. Even with the clothes that my mum made me go to school in, I just wanted to wear shorts that were vaguely near the knee, rather than somewhere up here [he points to the crease at the top of a spindly thigh]. I suppose that's why I now get a kick out of communicating on a mass level."

It wasn't just sartorially that Jarvis was marked out from the crowd at an early age. Like another shamanic pop performer, Johnny Rotten, he survived a childhood bout of meningitis. "I've since realised that there was quite a big chance that I'd die. They got all the class I was in at school to write letters - they didn't exactly say 'sorry you won't be around for much longer', but they wouldn't have gone to so much trouble if they didn't think I was on my way out."

When Jarvis didn't, in fact, die, all his get-well gifts had to be destroyed because of the risk of infection. "The only things I was allowed to take home" he recalls poignantly, "were a couple of cheap plastic spacemen that could be sterilised in boiling water." As well as a keen understanding of the nature of anti-climax, the five-year-old survivor was also left with permanently impaired eyesight. Needless to say, his class-mates did not react as sympathetically to his new glasses as they had to his impending demise: in short, "they pissed themselves".

When Jarvis was seven his dad went to London to look for work, and thence to Australia to avoid paying alimony. "I suppose I might be inventing this", says Cocker Jr, "but I don't really think I was all that bothered." Is it right that his mother was a bit of a bohemian in Sheffield terms? "Yeah, but I mean [a pause] that's not very bohemian. She used to go hitch- hiking in France and she had a couple of Miles Davis records, but she was around all through the Sixties, and she only smoked dope for the first time about five years ago."

Cocker justifies his reputation for candour - pop stars don't usually tell you when their mothers first smoked dope. He has ascribed the disarming frankness (both in person and in song) of his approach to the private and especially the sexual side of life to growing up in predominantly female company. Whatever the reason, no one is going to deny this man access to his emotions. He has long delighted in tormenting audiences between songs with hilariously extended meditations on what exactly he or they might be feeling at any given moment.

Anyone privileged to witness Jarvis' performance at this year's Glastonbury Festival will have seen him hold 50,000 people in the palm of his hand. The most notable of the songs that he eventually got around to singing was Sorted For E's & Whizz, a sublimely jaundiced look at the rave scene of 1989. In it, Jarvis uses his inability to secure a lift home at the end of a hard night's mass hedonism as a metaphor for the failure of Acid House's dream of community.

"Even if it was all drug-induced, I thought it was the start of a big change in people's attitudes", he observes, "people being friendly while they were out rather than wanting to have a scrap. I just thought it would seep into the rest of people's lives, that if you're nice to people life is more fun, but it didn't." Wasn't it a bit cheeky, though, to make that point at Glastonbury? "I suppose you don't want to have something commented on while it's happening", Jarvis concedes.

But the willingness and ability to comment on things while they are happening is one of the secrets of his success. On Pulp's long-awaited first Top of the Pops appearance, Jarvis took advantage of live TV to pull open his jacket and reveal a bit of paper bearing the legend "I hate Wet Wet Wet". He seems genuinely bemused that head-Wet Marti Pellow was sufficiently upset by this to threaten physical retaliation. "If he said he hated our group - as I'm sure he does - I'd take it as a compliment."

Jarvis Cocker has been practising being a pop star for the past 30 years. Now he actually is one, he's determined to get it right. If this means punching the air in triumph after (correctly) answering all the questions in the quick-fire round of Pop Quiz, or reciting the whole of John Miles's Music Was My First Love to a profoundly unsettled Mercury Awards dinner, then so much the better.

There is still work to be done, though, before pop music again occupies a central position in the lives of all the nation's youth. Jarvis wrinkles his nose at Brit-pop, the compound noun of the moment - "It's so ugly" - and is well aware of the almost Merseybeat-like genericness of so much of the music being released under its banner, but is hopeful about the next few years. "I think we're in 1963 at the moment," he observes with cryptic optimism, "1965 will be a lot better. We're hurtling towards the end of the century and people are desperate to find something of substance."

And that is just what the fearlessly autobiographical Jarvis is here to supply. From the beautifully crafted libidinous psycho-dramas of Sheffield adolescence with which he first caught the public ear, to the inch-perfect social and sexual observation of Pulp's new album Different Class, Pulp songs are a triumph of content over style. As with their last single Common People, the hilariously anthemic satire of downward mobility that propelled Pulp into pop's premier league, the raw material for the new record comes from the years after Jarvis moved to London to do a film course in 1988.

Is there a danger that the deep well of his personal experience might one day run dry? Jarvis, who would never write a song about hotels, touring or interviews as a matter of egalitarian principle, seems to think so. "My life", he says wistfully, "now consists mostly of things I wouldn't want to write songs about." But presumably that's a kind of liberation? Before, anything he was doing might one day have to be twisted into a little piece of art. Now there's a vast slew of stuff he can just get on with. Jarvis brightens somewhat. "That's a very positive way of looking at it", he pauses, his eyes finding room for a little bit more of the devil. "I've kind of got carte blanche."

8 Mis-shapes / Sorted For E's & Whizz (Island) is out next Monday. Tour and album follow in October