In the fickle world of music, memories are short. It's all about freshness and current fads, leaving little room for old incumbents to find repeat success.

When the audience's interest has switched from CDs to MP3s, how does a band stay culturally and musically relevant? What is the winning formula for long-play longevity?

Commercial mainstream success often comes at a cost - usually the disintegration of all-important street credibility.

But after putting up with the 'postcard punk' label for many years, Green Day seem to have hit the nail on the head.

Stick to a simple formula - three minutes, three chords and catchy snarling lyrics. Build up a massive teen following. Disappear off the scene for a few years until everyone's written you off as a wasted bunch of has-beens. Then bounce back with a concept album that has even the most sceptical of music observers piling on the accolades.

Anyone doubting that Green Day have retained their massive fanbase in Britain during their layoff might be suprised to learn that, due to unprecendented demand, a second date at Milton Keynes National Bowl on June 19 has just been added to their current sellout tour of the UK.

Regularly host to top performers like David Bowie, Robbie Williams and Michael Jackson, the Bowl has a capacity of 65,000 and will be the venue for the band's biggest shows on British soil.

The band's most recent album, American Idiot, was released in August 2004 and confounded the critics. The trio of Californian skate-punks may still look the part they first played in the early Nineties, but don't be deceived by the panda eyed pogoers. Beneath the heavy khol of Green Day 2005 lies a newly awakened political conscience.

Centering around two five-part, nine minute epics (Jesus Of Suburbia and Homecoming), American Idiot is an expansive and carefully-crafted concept album that details the alienation and disillusionment of the average American citizen under Bush's war on terror administration.

Produced by Rob Cavallo, the record has now sold five and a half million copies to date worldwide.

The band wrote the songs for American Idiot at about the same time that the United States began invading Iraq. For frontman Billie Joe, who was becoming increasingly frustrated with his government's actions, the war quickly become the dominant theme.

"I am anti-war so a lot has to do with that," he says.

"The song Holiday is about a mishmash of people with all these strong opinions who really can't agree. So they leave the decisions to the guy who's sort of standing in the middle, confused and overwhelmed."

"I hope that guy - Bush - will get put on trail for war crimes."

But with Dubbaya being re-elected, it seems that despite its success American Idiot didn't really make any difference to the outcome of the US election.

Billie Jo disagrees, remaining convinced that although they got the wrong result the record succeeded in making young people think about politics again.

"We didn't expect to win the election for John Kerry'" he says.

"But more young voters came out because of people like us and other artists speaking out."

Some people have suggested that the band protest too much in their anti-war stance and recent political awakening. The album came about after the tapes of 20 tracks they had been working on - by all accounts their trademark pithy punk anthems - got stolen from their recording studio in Berkley.

Lacking the motivation to re-record the songs, the band chose to channel their frustrations into new material. A chance comment about a 'rock opera' then produced a flash of collective inspiration.

Billie-Joe says: "We were like, this is what we should be doing, this is how we're really getting our rocks off right now. We thought: 'lets's just be ambitious as hell and go for it', and from there it just started to get more serious.

"We're not just doing the same old thing again - having 13 songs and putting out a single and doing a video. That's become the new pop for a lot of rock bands.

"They're so f****** boring because they don't challenge themselves. That's what rock records I grew up on did. We thought: 'let's push it out to heights that nobody's doing right now'. We wanted to challenge people the way artists like Outkast and Eminem have done."

Current band members Billie Joe Armstrong (guitar, vocals), Mike Dirnt (bass) and drummer Tre Cool (aka Frank Edwin Wright, who replaced the original drummer Al Sobrabrante) have impressive Bay area credentials.

Growing up, they were all part of the northern Californian underground punk scene. Aged just 12 Tre became a member of The Lookouts, and childhood friends Billie Joe and Mike formed their first band, Sweet Children, in Rodeo California when they were just 14 years old.

In 1989, after changing their name from Sweet Children to Green Day, the original line-up of Billie Joe, Mike and Al released their first EP, 1,000 Hours, independently.

But it was not until 1994, when Al had been replaced by Tre, that the band really launched themselves in to the big time with the release of Dookie, their debut album on major record label Reprise. Reprise was formed in 1960 by the king of crooners himself, Frank Sinatra, in order for him to have more artistic freedom for his own recordings.

Ironically it was sold just three years later to Warner Bros Records, now a division of Warner Music Group.

Dookie was a sensation among the American mainstream - selling over eight million copies - but it also caused considerable controversy in the punk rock community, with many critics quick to accuse the band of selling out. But when asked how he can reconcile being a punk band on a major label Tre is sanguine: "How do I reconcile? Why should I have to reconcile?"

"This band doesn't have a guilty conscience about anything," Billy Joe adds. "We don't regret anything. Even playing with Bon Jovi was kind of a trip."

This uncompromising attitude makes the band stand out from their predecessors. Spawning a whole generation of MTV punk bands like Limp Bizkit, they remain resolutely unapologetic.

"We're proud of those bands!" Tre says.

"They can make a living and make music that I'd rather hear than Britney Spears, even if it doesn't have a lot of substance. I'd rather listen to guitars."

Green Day may revel in being "opinionated troublemakers" but they were initially regarded simply as punk revivalists. Although their music wasn't particularly innovative they brought the energetic sound of late Seventies new wave punk to a whole new younger generation.

This sanitised Clash sound elevated them to the forefront of post-Nirvana American alternative bands, surpassed only by godfathers of grunge, Pearl Jam.

Meanwhile the battle between mainstream acceptance and the band's punk roots seems to be one mainly played out by the music press. The band themselves have never had any qualms about mass accessibility and call American Idiot their public response to the confusing and "weirdly warped world" of the American music scene.

The political content does make it stand out from anything they have done in the past and may be a reflection of the band's growing maturity. But it could equally just be a cynical cashing in on America's growing discontent with their political leaders.

With George W back in power it remains to be seen whether Green Day have, as they claim, "united and politicised young voters in a way that's relevant to them".

Either way, it is unlikely that The White House will be showing too much interest in these cranked-up expressions of political angst, but with a new generation of fans behind them Green Day's energetic punk posturings remain infectiously catchy.

Starts 6.30pm, tickets cost £22.50 (SOLD OUT). Call 0870 900 9100