Fleet Foxes: Are a hairy bunch of young folk-rockers inventing a new sound of Seattle?

The Junction in Cambridge is a nondescript venue: a white box, plonked in the middle of a retail park surrounded by gaudy chain restaurants, overlooked by a terrifying giant snowman. This is all that Fleet Foxes – Seattle's greatest musical export since you-know-who – will see of the city, but they're probably too exhausted to care, having already completed a dozen or so dates on their sold-out UK tour. Backstage in a dressing-room, marvelling at the hundreds of penis drawings on the walls, lead singer and songwriter Robin Pecknold sighs long and hard.

"This year has been really long," he mumbles through his blonde beard. No wonder – 2008 belongs to them. In just a few months, Fleet Foxes have gone from near-obscurity to critics' darlings, both here and across the Atlantic. Not bad for a band whose brand of gorgeous folk-rock sounds as old as the hills. "I feel like I've aged five years," says Pecknold, who, at 22, looks five years older than he is. (Few 22-year-olds have the ability to grow such a formidable Nordic-fisherman's beard.)

Pecknold has an old soul, and his band's sublime, self-titled debut album reflects that. Its cover artwork, for example, is one of Pieter Bruegel the Elder's 16th-century peasant landscapes, and there is something of the madrigal to Fleet Foxes' mournful melodies. Their influences, though, are more recent – the band sound like the heavenly, harmonising love child of Brian Wilson and Crosby, Stills, Nash & Young. But what raises the album above an exercise in wilful nostalgia are the songs; the fully-formed, adventurous, textured songs.

The album was released to rave reviews in June – a few months after their hit EP Sun Giant – and as the summer went on, the gospel spread. Make no mistake: Fleet Foxes is the album of 2008. If that sounds faintly hysterical, well, maybe it is, but Fleet Foxes' fans are a little hysterical – in a silent sort of way. As their chatty keyboardist Casey Wescott tells me before their Cambridge show, "It's crazy when you get that many people in a room, with alcohol, and can still hear a pin drop."

Pecknold would not agree with such reverence. "I don't feel we've done the best we can," he says. "If people think it is, that puts you in a weird place. Where do you go from there? We have an infinite number of ways to improve."

While Fleet Foxes might sound like they were beamed in from late-1960s Laurel Canyon (their live repertoire includes a Judee Sill song), one of Pecknold's greatest influences is the contemporary folk singer Joanna Newsom and her experimental, orchestral second album Ys. "The best records for me are the records that have their own logic, when you have to listen to the whole thing," he says. Recently, he told the music website Pitchfork.com, "[Newsom] is a pretty singular entity. It's fine that we're not there yet, and I definitely want to get to that place."

This, perhaps, is why the band are itching to get back to their home studios in Seattle and show the world what they are capable of. "When we started recording, we had no idea what we were doing. Now we go back to the record and it's like listening to demos."

Few musicians would be so honest about their own work – especially when swathes of their audience would vehemently disagree. But Pecknold is more musically ambitious than most swaggering band-leaders. As a child, he was overweight and had few friends, preferring to spend his time idolising Bob Dylan and the late singer-songwriter Elliott Smith. "The thing I found intriguing about them is that the song wasn't for everyone else.

It almost sounded like a diary entry – and not like a Kiss song, which is for 10,000 people."

Fleet Foxes – as he describes it – "was pretty accidental". The band is built around Pecknold and guitarist Skye Skjelset, who met at school and bonded over their love of music and shared Norwegian heritage. Back then, they were called the Pineapples. "It was just an excuse to record the music I wrote," says Pecknold. "And then, when we started meeting other people and a band formed, it was like, 'This is fun to do at home – let's play a show!' There was no masterplan."

Band members have come and gone, but the current line-up is here to stay, with Pecknold, Skjelset and Wescott joined by Christian Wargo on bass and guitar and Josh Tillman – a singer-songwriter in his own right – on drums. All provide vocals for those heaven-sent harmonies – and all are reluctant to be described as a Seattle band, despite being signed to Sub Pop, the quintessential grunge label. During our conversations, the word "grunge" is implied but never spoken.

"We don't represent Seattle, we represent ourselves," says Wescott. "I know the city was known for a certain thing. On a functional, creative level, I'm not thinking about Mudhoney. You know what I'm saying?"

Indeed, there is not much to tie Fleet Foxes to early-1990s Seattle, the city's most famous musical era. But Pecknold is slightly reminiscent of Kurt Cobain – not in a nihilistic sense, but as an artist. Despite his self-deprecating shyness, he knows just what he wants. Without him, there would be no band.

But the rest of Fleet Foxes are no backing band; each is integral to the recording process and they are, unlike many bands, really good friends. "Everybody's creative life gels really well," says Wescott. "There's no in-fighting and we're becoming each others' only friends." And he has only good things to say about Pecknold: "As the main songwriter, he isn't afraid of other people switching stuff up. He's not insecure. His mind works really fast and he wants things to be the best. It's as close to a democracy as a band can be."

Back in Seattle, Wescott was almost having a nervous breakdown trying to juggle his band duties with his job as "a software-developing, project-manager consultant dude". Tillman was a woodworker, Wargo was bartending, Skjelset folding T-shirts and making coffee, while Pecknold was rolling burritos. As Tillman puts it, "We don't have anything to complain about now."

The band are not, however, interested in the usual excesses of life on the road. "Sometimes we get invited to bands' after- parties," says Wescott. "What does a band have an after-party for? Aren't they tapped out?" Tillman agrees: "There are certain kinds of bands where the songs are just host bodies for an attitude or style. We're more excited about the creative process."

When Fleet Foxes were recording their debut album in Pecknold and Wescott's homes in Seattle, this level of success was the last thing they expected. "My initial thoughts were that we would put out the record, do one US and one European tour, then get to work on the next one," says Pecknold. "It's turned into four US and three European tours. It's endless." And it goes on. Over the New Year, they'll be playing sold-out shows in Australia and New Zealand, then it's back to London for another bout. After that, the pressure will be on to better their debut album – but they seem to relish the challenge. "I just want to work on more music," says Wescott. "After a year of touring, I think it's time to start a new chapter. I'm excited."

Fleet Foxes are playing the Roundhouse, London NW1, from 22-24 February 2009 0844 482 8008, ( www.roundhouse.org.uk)

Rough harmony: Where Fleet Foxes found their sound

Steeleye Span

"British people think this band is dorky," says Pecknold, "but I love them." Steeleye Span were a central force in the 1960s British folk revival and are best-known for "All Around My Hat", which was based on a 19th-century folk song

Crosby, Stills, Nash & Young

Possibly the most influential super-group of all time, Californian folk-rock legends CSNY are one of Fleet Foxes' most obvious influences, primarily in their use of vocal harmonies. They still perform occasionally.

The Zombies

"The Zombies album Odessey and Oracle is really amazing," says Pecknold. "It's a flowing experience. I wanted our record to be like that." The Zombies were overlooked at home in the UK, but their 1968 record is now a psychedelic classic

Elliott Smith

"The first stuffI recorded was like Elliott Smith," admits Pecknold. "Really quiet acoustic guitar stuff." Smith was one of the great singer-songwriters of the 1990s, known for his multi-tracked vocals. Having battled depression, he committed suicide in 2003