The Super Furry Animals: When Paul McCartney played the celery

'We always felt like spectators, outsiders to the whole thing." Gruff Rhys could be talking about anything. Taken in isolation, it's a statement which could serve as a precis of the Super Furry Animals' entire career. In this instance, though, the placid, pensive SFA singer is referring to "that year when the Manics, Stereophonics and Catatonia went absolutely massive," that peculiar period between 1997 and 1998 when Wales, for so long the butt of cheap gags, suddenly and improbably became hip.

Not any more. Like Manchester, Seattle and Camden Town before it, South Wales is once again on the scrapheap of fashion. It's official: Cool Cymru is dead. A good thing, perhaps?

"Maybe it's become equalised, normalised," reckons Dafydd "Daf" Ieuan, the Super Furries' garrulous drummer. "At the time, lots of bad bands got signed because every record label had to have a Welsh band, but I also know good bands who didn't get signed because the record companies thought, 'Welsh bands? We've already got one of those'. At least now Welsh bands have a chance. The idea of a band coming from Wales isn't a novelty."

A lot has changed for SFA, too, in the past couple of years. The last time they made an album, it was recorded quickly and cheaply, written entirely in Welsh, and released on their own independent label. This time, it was recorded at considerable expense on both sides of the Atlantic, written entirely in English, and is being released by the biggest record company on the planet. Last time I interviewed them, they were huddled around a coffee table in their office above a discount hi-fi store in Cardiff. This time, they're in the bar of one of London's most elegant old hotels, prodding at a plate of six nouvelle cuisine chips, arranged in a pile like an edible game of Jenga.

Two years ago, victims of the fallout surrounding the sudden demise of Creation Records, SFA unexpectedly found themselves without a label. Although theoretically still signed to Sony (owners of Creation), they exploited the chaos by seizing the opportunity to do something they'd always wanted to do: an album in their mother tongue, released through Ankst, the Welsh-language label owned by their manager, Alun.

It was a move misinterpreted as a political statement on both sides of the linguistic divide, but for the Furries, who all consider Welsh as their first language, it made perfect sense. Mwng, a beguiling and charming record regardless of whether the listener could understand the words, became the best-selling Welsh-language album of all time.

The psychology of bilingualism is fascinating. Are they translating their thoughts in their heads as they speak to me? Or does a different part of the brain automatically kick in when they speak English? "It's not as if I press a special switch in my head and start speaking English," says Huw "Bunf" Bunford, co-singer and guitarist. "But there are jokes in Welsh that, if I translated them into English, wouldn't be funny." The idiomatic differences can be useful: alternating between languages helps keep their songwriting fresh. "I could write another Welsh album tomorrow," says Gruff, "but it would be crap. In another year, I might write Mwng Part II and it would be brilliant." A cynic, of course, might wonder whether the decision to make their new album Rings around the World an all-English affair is driven by Epic, their new paymasters, in an attempt to make it more radio-friendly. "We think all our music is radio-friendly," protests Daf. "It just doesn't get played on the radio."

This, of course, is crazy. "Juxtapozed With U", the absurdly catchy current single, is the most radio-friendly thing SFA have ever done, a piece of summery disco with a production straight out of 1975. They mention Marvin Gaye and Caetano Veloso as inspirations for the song, although they nod in agreement at the mention of Philadelphia soul, and David Bowie's "plastic soul" approximation of it on Young Americans. "It was important that it should sound as plastic as possible. If we'd tried to make it sound authentic, it would have been awful."

Anyone who's only heard the single will be surprised by the track that precedes it on the album, "No Sympathy", which has the hookline, "You deserve to die" (this from a pacifist band who have previously espoused non-violent direct action). "It's an album of extremes," Gruff admits. "I originally wrote that song for a film called Plop that was made by a group called Fukme 99 – a parody of Dogme – about a group of people who live as if they were living their last days, and when I was watching the film, I couldn't feel sympathy with any of the characters. I wanted them all to die. Out of context, it sounds quite aggressive. Each time I sing it, I have a different person in mind."

As one has come to expect of the Super Furries, the album is thematically eccentric, leaping from religious fundamentalists to modern telecommunications and the old Hollywood star system with disorienting glee. It also features some of Gruff's most openly romantic lyrics yet. The most striking example is "Presidential Suite", a big, showstopping movie theme of a song, reminiscent of Bacharach or Barry, with massed strings and John Cale on piano. Another lovestruck moment is "Sidewalk Serfer Girl" (sic), although Gruff admits he "cringes" when he hears it. "I try not to write about love in an obvious way. That's why I added a bit about Patty Whitebull, the woman who fell into a coma for 15 years then woke up one day and ordered a pizza."

For the affluent and gadget-happy, there's a special DVD version of the album (apparently the first of its kind). "We were originally going to make a film to go with the Guerrilla album, but it was too big a project, so this time we gave a different song to different people: video directors, website designers, T-shirt makers, mainly people in Cardiff." The results are heavy on cyber-visuals and animations, with an eye-boggling film for each song.

Perhaps the most-discussed song on Rings is "Receptacle for the Respectable", a song which, so legend has it, features the sound of Paul McCartney chewing carrots and celery as a percussion track (a service Macca had previously provided, over 30 years ago, on the Beach Boys' "Vegetables"). Surely an urban myth?

"No, it's true!" says Gruff. "We'd already worked with him [on his Liverpool Sound Collage project], and when we phoned him up, he said, 'You're fucking mad, you are! You mad bastards!' But he agreed to do it. It took six months to organise. It was really cloak and dagger."

It'll justify the effort once word gets around to Beatles completists. Could be worth a few thousand extra sales. "I'd never thought of that," ponders Bunf.

'Rings around the World' by the Super Furry Animals is released by Epic