Don't mention Tom Jones

Don't be fooled by the name. Super Furry Animals are anything but sweet and fluffy. The band who once arrived at the Reading Festival in an Army tank are in a deadly serious mood. Languishing on a black leather sofa in Creation Records' cramped offices in north London, lead singer and guitarist Gruff Rhys doodles with a black felt pen on the lid of his coffee cup. A deep frown clouds an otherwise perfect pop-star profile, part youthful Howard Marks, part Celtic Mick Jagger, with a bit of Liam thrown in for good measure.

The focus of his contempt is the Welsh Assembly celebrations last week, where Tom Jones and Shirley Bassey, among others, turned up to perform. "Of course it's embarrassing," says Rhys, in a disconcertingly gentle Welsh lilt. "It's also tasteless and sentimental. We're not sportsmen; we don't automatically represent our country. We don't fly flags."

He picks up his mobile phone and starts fiddling with it. SFA guitarist Huw "Bunf" Bunford sits next to him, toying with a small pile of tobacco on the glass coffee table. They both seem happily diverted.

SFA have always been intriguingly aloof; when they emerged at the height of Brit Pop five years ago no-one could categorise them or define their sound. A couple of years later, Cardiff was hailed as the new Seattle, but for SFA the Welsh rock renaissance label didn't stick. They found it hilarious. "I once tried to start a new music scene," recalls Gruff. "It was called Dyfed Sludge but it didn't take off."

Apart from the fact that they sing songs in Welsh, there's very little reason to link them with other bands from Wales. While the Manics, Catatonia and Stereophonics lean towards a rock stadium sound, SFA are far less conventional. At the moment they're being linked with groups such as The Beta Band,The Flaming Lips, Spiritualised and Mercury Rev as part of the supposedly "Nu Psychedelia". Another label, another misnomer. Gruff laughs, "It's mildly diverting but we could do without it. We've never been self- consciously psychedelic. We're trying to do our own thing, creating an eclectic blend of psychedelic whimsy, raucous electronic rhythms, folk, and lush Beach Boys harmonies that never quite sounds like anybody else's."

Somehow Super Furry Animals have remained steadfast outsiders, refusing to align themselves with any particular cause, identity or group. "We're always being pigeon-holed but we're not pigeons," says Gruff, sweetly and without a trace of irony.

Too weird and original to be fully mainstream, too melodic and catchy to linger underground for long, they seem perfectly content to teeter between the two, promising one while playing at the other.

Now, though, there are whispers of mainstream success with their latest album Guerrilla, which they produced themselves. Rumours circulate that it's a Mercury Prize contender and suddenly they're surrounded by a lot of hype. Gruff, who is 29, puts this down to the fact that they're less of a risk, in critical terms at least. "I think it's because people don't have to put their neck on the line. We've got a big following and our live shows aren't so crappy. We're a band they can deal with."

Their most recent single, "Northern Lites" went into the charts at Number 11, one place higher than last year's "Ice Hockey Hair". According to Gruff (pronounced Griff), Guerrilla is "flippant, exciting, with an instant pop rush". Like Supergrass, SFA's brand of pop sensibility tends towards a childlike exuberance and enthusiasm, rather than super-cool introspection and angst.

Which comes as something of a relief after the arch seriousness that mainstream bands such as the Manics, Radiohead and, until recently, The Verve have tended to embrace. "We wanted this to be an immediate album. At first we did want to make a lyrically reflective, deeply emotional one but decided to go for the grooviest." Not that SFA don't do serious. "There's much darker stuff to come," says Gruff.

Guerrilla, though, is more of a summer album. "Northern Lites" is a mix of Sixties pop and calypso rhythm united with some strange lyrics about the weather. "It's about El Nino," explains Gruff. "We don't like to sing about any old weather. El Nino is a terrifying, worldwide, seven-year phenomenon. We like the extreme stuff." Yet they could just as easily be singing about a cloudless day on a Brazilian beach. Promoted as more of a pop album than their other two, Fuzzy Logic (1995) and Radiator (1997), Guerrilla still contains a fair amount of whimsy and skewed imagination. "Chewing Chewing Gum" sounds like one of Brian Wilson's more wistful out- takes from Pet Sounds while "Fire In my Heart" is a melodic, yearning love song.

They seem quite reluctant to divulge specific musical influences, although all their albums seem to draw from diverse sources. "The first thing I remember is Welsh-language pop, Edward H Davis and a Welsh pub rock band Ail Symudiad," says Gruff. The first English record he bought was, he says, "Father Abraham and the Smurfs". He also used to listen to his brother's music: Black Sabbath, the Undertones and Bob Marley.

Gruff and Bunf met in Cardiff about 10 years ago and formed a band soon afterwards. By the time Gruff had finished studying art at Manchester Polytechnic, he'd completed three albums. "We have always been ambitious but it took about two years for us to get it together," says Bunf. Yet five years later some critics have accused them of being under-achievers, perhaps because they're not as self-aggrandising as, say, Oasis. Certainly they don't brag about worldwide domination.

So what is it that motivates them? "We're not interested in being big pop stars," shrugs Gruff. "Our needs are primarily in musical adventure. Also we want to alter the musical climate. It's too formulaic. For instance, why do all pop songs have to be in English?" This leads us to another focus of Gruff's contempt: "The music industry is the most banal thing in existence," he says. "Who cares if records sales are going down? People are being ripped off. When musicians are in it for the wrong reasons, the public susses it out. Although you do need the crap music to react against."

For a band that supposedly isn't that ambitious, SFA are impressively prolific. No painful five-year breaks working on a tricky second album for this lot. Next week they start recording an album in Welsh, and after that there's an instrumental one planned. In the meantime Gruff is heading back to Cardiff where his girlfriend lives. "I like to keep a healthy distance from London. I don't want to be like the rest of the ants in the machine." Odd. Very odd. But all the more charming for that.

'Northern Lites' is out now; 'Guerrilla' is released on 14 June; SFA play Glastonbury Festival 26 June