There is always one constant in the ephemeral world of pop/rock and that is, quite simply, that Metallica rock. And they do so in a most magnificent way with their Mach 3 guitar sounds proving to be as riff-tastic as they come. There aren't that many nominally metal bands who can successfully shake off the woeful excesses of the genre, but with their sheer bang thump bang sound, Metallica not only bypass the usual limitations but also summon up a type of Route One approach to rock music that is as impressive as it is direct. There has never been any clever wordplay, any layered melodies or any particular originality to their work, but for sheer rock, they're yer only man.

With a career that at times touches on Spinal Tap-isms, they have weathered most of the storms in the metal sub-climate. While grunge killed off their poodlehaired, 15-minute drum solo effete cousins, the US band merely tweaked their sound over a 16-year career and are now one of the biggest unit shifters around. From the Los Angeles underground metal scene, they were formed by the "Lennon and McCartney of metal", lead singer James Hetfield and drummer Lars Ulrich in the early 1980s. The debut album Kill 'Em All was pure trash metal, although with a bit more depth (though not much, mind you) than is normally associated with the sub-genre. It wasn't until the Master Of Puppets album that they came to be regarded as the foremost metal band around. Lyrically, Hetfield based it around the concept of justice; ranging from songs about the First Amendment to war, the album included the stand-out track One, which was also their first-ever video and introduced them to a massive worldwide MTV audience.

Despite all this, they were always frozen out by the mainstream media as "hairy, metal types" and with virtually no radio play and no press exposure, they relied on their hardcore fan base to help their records chart. There were also signs, though, that this was a band which wanted more than just the respect of the metal community. By slightly varying the production and making the songs shorter, their Metallica (or Black Album) album won them a bigger and newer fan base, and sold 10 million copies into the bargain.

Criticised by some for getting their hair cut, embracing "alternative" rock (i.e. grunge) and having their photos taken by Anton Corbijin, they lost many of their early fans by the time of the Load album in 1996. They were especially despised for agreeing to headline the Looapalooza tour and while some felt they had "sold out", more felt they were challenging the limits of metal. Now back with a new album, a double album full of cover versions, we asked James Hetfield, why covers and why now? "We're doing these songs because we like the bands and when we were growing up and were sponges for music, these were the bands that really helped mould Metallica," he says. "It all came about because of a question someone sent in to the Metallica club that asked what non-Metallica song we would have liked to have written; and our answer to that is all the songs on this album."

It's no surprise to find Black Sabbath, Motorhead, Diamondhead and Merciful Fate songs on the album - but a Discharge song? "I discovered them from going to a Motorhead show," says Hetfield. "I was looking around me and there's all this green spiked hair and Discharge and GBH shirts. So that really turned me on to some of the punk stuff."

There's also a Nick Cave song on there - Loverman. How did that come about? "We're big fans. I think we pulled it off with that song; we managed to retain the spark of the original whilst still adding our own identity and our own little touch to it," he says.

The cover of Whiskey In The Jar sure beats the one by Pulp; you're obviously a big Lizzy fan? "I've been a fan for ever, and picking Whiskey In The Jar was because we didn't want to do the obvious, The Boys Are Back In Town. For us it's a more obscure song of theirs and it's actually not theirs at all, it's in the public domain. It's been around for hundreds of years, I've heard." Too right. Have to ask you about Sabbra Cadabra? "When I was 10 I got a Black Sabbath album as a present and to this day I can clearly remember sitting and just playing Sabbra Cadabra over and over and over again. It's a song that not everybody knows necessarily, it's not like Paranoid or anything like that."

Any word on a new Metallica album? "Yeah, the goals are already being set and we want to keep moving forward. We want to keep ahead of the game, like we have been for a while. It's just a case of having a big plan on what has to happen and what needs to take place for us to continue being the big, big, biggest heavy band around."

Garage Inc. by Metallica is on the Vertigo label.