Bank holiday Sunday and the hordes have descended on Bramham Park in West Yorkshire for the last day of the Carling Festival. As soon as you walk through the gate there is an all-too-familiar assault to the senses - the stench of cheap burgers and beer; the suck of mud under foot; and the sight of acne, ra-ra skirts worn with rubber boots, and men urinating against every available upright surface. Oh, and the inevitable sound of some dreadful nu- metal band thrashing away on the Radio One stage. When it comes to the big, outdoor pop extravaganzas I'm with Edwyn Collins, who has been known to sing about ''the truly detestable summer festival''. The Carling Festival lives up - or should that be down - to

But it probably looks rather different if you are performing. It is teatime when Franz Ferdinand saunter onto the main stage, look out across a multitude of bodies and launch into 50 minutes of their trademark spiky pop. Two songs in and half the audience is singing along, word-perfect, to Jacqueline. By the time they kick off Take Me Out, the crowd has become a single organism bouncing along in time to the music.

A year ago, Scotland's brightest new stars performed at the same festival. Then, though, they were playing on the Carling Stage, sandwiched between such musical giants as Rocket Science and Billy Titan (no, me neither). This evening they are on the main stage, fourth in line of importance behind the White Stripes, Morrissey and the Libertines (surely more a rock 'n' roll soap opera than a band these days). Much has changed in 12 months. Franz Ferdinand started the year with a top-three single. Their eponymous debut album, released in February, is already almost two million sales to the good and up for the Mercury Music Prize. It's gone gold in the US and, in a few days, the band are going stateside again, hoping to improve upon that with, among other things, an appearance on The David Letterman Show at the start of October. They've been profiled in Time magazine, which reckoned they were

''hotter than a Paris Hilton download'', and graced at least half a dozen NME covers, beginning back in January under the banner headline: ''This band will change your life!''

They've already had a writer from the NME talk to them today. And every time they venture out to the guest area outwith their backstage dressing Portakabin there are fans clamouring for autographs, for photographs, for a little bit of their time. These days everyone wants a slice of the four twentysomethings. So yes, a lot of things have changed for Franz Ferdinand. But not the most important thing, declares Alex Kapranos, their razor-cheeked, dark-eyed frontman, after he comes off stage.

''The one thing I'm really glad about is the fact that the dynamic of the band doesn't feel anything different. That was something we were a little bit worried '' He pauses, looking for the right word, something he does a few times during our conversation. ''Not worried about,'' he continues, ''but aware of. Even before we had any success, we said, 'Look, we're four friends here, we can't lose that. We've got to make sure we don't.' But I think we've been quite fortunate. We've kept our heads and it feels like the same four people that were here last year who hadn't released any songs.''

If anything, they are even closer than before, according to bass player Bob Hardy - at 24 the baby of the band and invariably described as ''cherubic''. That increasing closeness is perhaps to be expected. After all, he says: ''We practically live together on the tour bus.''

The touring life has yet to pale, though. ''When you list all the events we've done this year it's like ten years' worth, or something like that,'' says Kapranos. ''Yet it seems like hardly anything at the same time.''

Kapranos is the most vocal of the four, the one most happy to talk to the press - though none of them hides behind pop-star hauteur. If anything, they are amazingly approachable, with, as yet, no nouveau celeb pretensions. Indeed, Paul Thomson - ''the good-looking one'', according to his wife, Esther, though she might be a little biased - is still starstruck by the rather less famous musicians he has spotted today. ''I've just met TV on the Radio and Pink Grease, and I'd imagine we've sold more records than both of them combined, but I still feel an idiot talking to people like that,'' he says.

Thomson is the band's skinnymalinky drummer. Broken-toothed and kiss- curled, he's got matchsticks for legs and pipecleaners for arms - arms currently swathed in a Christian Dior jacket. Designer labels are one of the discoveries of the last few months. ''We've started getting free things from some designers,'' Nick McCarthy, the final member of the quartet, tells me. ''You should see us when a goodie bag comes in.'' A pair of Paul Smith boots lie discarded in their Portakabin. ''I like Paul Smith,'' McCarthy says. ''But I actually like the girl's stuff.''

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He'd never actually buy a designer label, though. ''It's weird,'' adds Kapranos. ''We've just made this transition from basically wearing second-hand clothes from Oxfam and Cancer Research or wherever. And all our wardrobes are a mixture of the two. But we have the same mentality about it. Everybody treats their clothes in exactly the same way as they treat the clothes they got from Oxfam. It's just bloody clothes, come on.''

Well, yes, but one of the pleasures of Franz Ferdinand is that they're not a T-shirt-and- jeans band. They talk smartly (this is a band who discuss the artistic output of the Russian Constructivists, not a subject you'd imagine comes up much with Oasis). And they look smart. Presumably that's why Paul Smith has told them he wants to meet them. Is there a Franz Ferdinand dress code, then? ''Yes,'' says Kapranos. ''Wear what you want.'' So if someone turned up in a shellsuit then that would be fine? ''Nobody would.''

Style is important, then, and they know how to maintain it. For half an hour Kapranos talks to me in trousers split at the crotch. He finally ushers me and McCarthy out and sews the hole up. Without taking the trousers off. That's pop stars for you. Always living dangerously.

And it's clear that they are pop stars now - Top of the Pops regulars. ''It's like losing your virginity,'' says Kapranos of the show. ''It's a pretty extreme situation and you find yourself just doing it rather than being able to step back and savour it. Of course, afterwards you can.'' So which was better: Top of the Pops or losing your virginity? ''They both lasted about the same length of time. Less people watched me lose my virginity.''

It's clear that Franz Ferdinand's success has gone a little further than some of them seemed to expect. ''I've achieved everything I wanted to achieve,'' Thomson tells me. ''I wanted to sell 500 copies of a seven-inch single or something like that. I suppose I'd still like to do a [John] Peel session.''

But it's obvious Franz Ferdinand are long past the need for Peel's patronage. In many ways, what makes them interesting is that they always had aspirations rather greater than a trip to a Radio One recording studio. Coming from a Glasgow scene that in recent years has been a little guilty of a kind of wilful insularity, they've never wanted just to play to their mates in other bands. ''We were trying to do something a little bit bigger, and I'm not embarrassed to say that,'' agrees Kapranos. ''We didn't expect it to happen. We expected to sell 500 singles. But our ambition was to write the best pop song ever heard.''

The quest to write the perfect pop single began in the old 13th Note club in Glasgow, where Kapranos ran the Kazoo Club. ''I've known Paul the longest,'' says the singer. ''He was in a band in Edinburgh and I had them through for a gig. I got on with him and he used to come through and stay with me. We'd sit and talk about records and listen to records.''

Thomson, like Kapranos, was a face on the Scottish music scene in the 1990s, playing in various bands between grotty day jobs. At one point he was a life model. There'll presumably be a Thomson nude for sale on eBay any day now. ''A downmarket tabloid newspaper has already put out some hotline looking for one,'' Thomson tells me on one of the few occasions he is seen more than a few feet away from Esther. ''But for most of the time I was doing that I had a huge beard.'' The Joy of Sex look? ''Yeah. You wouldn't recognise me.''

Thomson and Kapranos were simpatico from the start. The same couldn't be said of Kapranos's relationship with the band's bassist. ''I met Bob through my girlfriend at the time. I was going out with a girl who was at Glasgow School of Art and her best friend was friends with Bob and we met for a drink and Bob told terrible, terrible jokes and I thought he was a complete buffoon, a total moron. But then I met him a couple of times again and really warmed to him.''

''Alex saved me from total poverty,'' Hardy tells me. ''He got me a job in a kitchen when I was a student at Glasgow School of Art.'' Kapranos, it transpires, was a chef at Groucho St Jude's in Glasgow and got Hardy a job as a KP. A KP? ''Kitchen porter.'' What, he'd peel potatoes and stuff? ''If he was lucky.''

It was, Kapranos tells me, a rock 'n' roll kitchen. ''Normal service on a Saturday night, we'd have the Stooges or the Velvet Underground or the Rolling Stones on the CD player amid all this frantic stuff like a function for 80 people - knives flying everywhere, hot fat flying everywhere - and everybody was in a good mood, getting on with each other. Bob and I had a good summer there.''

Nick McCarthy appeared at the start of 2002. The fourth member of the band had grown up in Germany, just south of Munich, where his parents had moved when he was a toddler. His father was an engineer who went to work with Daimler-Benz. ''He always wanted one of those big Bavarian farmhouses and he never got it. Maybe I'll get him one now.''

As a teenager he was a skater, long hair and all, before going on to study jazz double bass, of all things. ''I wanted to study anything - art or drama. But they took me at the music school and for four years of my life I concentrated on jazz music.'' It's a pity, then, that he doesn't seem to like jazz very much. ''With jazz I always have to cringe a lot. There's a lot of crap out there - so much rubbish, and it's so clean. I really like grittiness in music. It's gotta rock.''

He moved to Glasgow on the advice of an Orcadian accordionist who played with him in a German band. ''She said Glasgow was really cool. I lived in Munich for two and a half years and I wanted to go to somewhere that was the complete opposite of Munich, which is very clean, very straight. And Glasgow was totally the opposite. In Munich I thought I was the bad guy, and I arrived in Glasgow and it was, 'F-ing hell.' It was really gritty, really funny.''

He met Kapranos at a party. ''We had a fight, basically over something really pathetic and puerile,'' says the singer. A vodka bottle, according to legend. ''It was a wee bit ugly but it was like the sort of situation that happens in the schoolyard. It just flicks. It goes from an ugly situation to a fun situation and we started talking about music.''

''I was in Glasgow for three months before I met him,'' says McCarthy, ''and I was like, 'This is rubbish. I can't find anyone to play music with.' And he came over to my flat and started playing the piano, and I thought, 'Yes.'''

From the beginning, the four of them wanted to do things differently; to forgo the standard support-band route, for the most part, and make their gigs stand out. ''I'd been to Berlin a couple of times, to parties that had been thrown in abandoned warehouses, and Nick had been involved in similar nights in Munich,'' says Kapranos. ''We thought, 'Let's do something like that in Glasgow.' I didn't experience the dance scene of the late eighties but the idea of underground rave things sounded very exciting. I think we wanted to do a rock and roll version of that.''

And so they came up with the idea for their Chateau nights after finding an empty art deco warehouse overlooking the Clyde. They wired it up for electricity without telling Scottish Power and roped in some of the city's artists, who would put on exhibitions while the band played gigs on another floor. Those nights are already turning into myth: a bit like the Sex Pistols at the 100 Club, these days everyone claims they went to the Chateau. ''Did you go?'' Kapranos asks me. Afraid not, I tell him. I was probably washing my hair or something.

They'd have been a different band if they'd been based in London, Kapranos says. ''There was no media attention. That first year of shows we did, there was no press at all; there was certainly no music industry at them. But in London, if you start to gig then immediately there's five record-company guys down there. And if they're not interested, nobody will give you another gig.''

And Franz Ferdinand like to gig. That much is clear from the energy they put out on stage. McCarthy spends his time in constant motion; Kapranos, meanwhile is all flying kicks and saucy eye contact. He's slightly camp, I suggest to him after watching their set. ''I'd rather use the word 'theatrical','' he says, mock hurt. ''I think a sense of theatre has always been an important part of the best bands. If you look at Mick Jagger, David Bowie, Roxy Music, it's all about theatre. It's all about performance. Performance is everything. But that doesn't mean a huge set and not holding back; allowing a bit of your character out and, dare I say it, a little bit of charisma.''

In a couple of weeks, Franz Ferdinand will be heading off to Bologna and then on to America. Travel is the thing they all say they enjoy about the job - not that they see it as a job. There may even be something inevitable about their peripatetic existence. Ask them for their first memories and travel comes into all of them. McCarthy remembers flying to Germany when he was two; Thomson going to see his baby sister, Hazel, and being given a toy taxi at about the same age. ''I was obsessed with black taxis.'' Kapranos recalls standing on a cold, windy train station in the north-east of England, looking at his granny's shoes and ''feeling very warm and loved and safe''. And Hardy? Well, his first memory is tripping and splitting his chin on some steps. But tripping is still motion, isn't it?

For the next few days, though, the four of them are coming to a rest and taking some time off. McCarthy is heading for Salzburg and meeting his dad in Munich. Thomson will head home to London and catch up with what's happening in EastEnders and Coronation Street. Hardy is hoping to catch up with his washing in Glasgow.

Kapranos, too, is coming back to Franz Ferdinand's birthplace and his flat in Dennistoun, in Glasgow's east end. ''I was going to paint my flat and redecorate it and stuff, but I've decided I'm not going to. I'm going to keep it exactly the same for the rest of my life so it's exactly the same as it was when everything went weird. When I go back to the flat it feels like everything's normal again. Like I'm going to have to get up tomorrow morning and go for a lecture at Anniesland College.''

These days, of course, Franz Ferdinand are living a new normal. They're still a little bit amazed by it. McCarthy tells me he was recently up on the west coast of Scotland and went into an old pub there. ''They had a jukebox and they had us on the jukebox.'' Did you play it? ''No. We all sang Take Me Out as a karaoke in Japan, though.''

Who knows how long it will last? In ten years' time they may not be together. ''We were going to have a sweepstake to see which of us would die first,'' says Kapranos. ''A few months ago I thought it would be Bob,'' adds McCarthy. ''But he's certainly sobered up a bit.'' Even if the drink doesn't get him, Hardy - who always wanted to be an artist - says music's not something he wants to do for ever. But right now he's enjoying being a member of the band of the moment. They all are.

''That's the good thing about being in this band,'' says McCarthy. ''It's totally opened up for us. It just feels like we can do absolutely everything we want to.'' n

Franz Ferdinand play the Barrowland,

Glasgow, on October 15 and 16. The Mercury Music Prize is announced on Tuesday.