If four years is a long time for you and me, it's an eternity in dance music. What was fresh and fierce and funky in 1995 can sound remarkably old hat in 1999 - and that's before you take into account what's come and gone between then and now. As for the haircuts and clothes we wore back then, do you really want to go there?

For Leftfield's Paul Daley and Neil Barnes, the four years which have slipped by since they released their debut album have been odd ones. Leftism was the album which took everyone, creators included, by surprise. A collection where the bass was king, it simply refused to stop moving onwards and upwards, taking Leftfield from their natural habitat to a more mainstream des res.

By summer 1996, with one million sales in the bag and a world tour which had shaken many venues to their very foundations completed, it was time for the pair to return to the studio and dream it all up again. Given how long it's taken, however, "dream" may not be quite the right word.

Paul Daley is sitting in an untidy Sony Music boardroom and smoking like a trooper. Rhythm & Stealth is finally in the shops, the sun is shining and he's ready to talk about the three years Leftfield spent in a small, windowless room in north London. "When we finished Leftism, we weren't sure what people would think of it," he remembers. "Being the type of people we are, we didn't think it was going to end up like it did. We certainly didn't think it was going to turn into the thing it turned into and I'm not blowing my own trumpet here. We had to live with that reality and go with the flow. We definitely felt the pressure from it when we went into the studio to make this one. We simply weren't expecting that level of success.

"When we started Leftfield, there was all this technology we could use; it didn't matter what you looked like, it was like an anti-1980s pop star enigma thing. And that's why we loved it; we were making records at home - and two weeks later, DJs were playing them in clubs and kids going mad to them. The thought of becoming pop stars or even successful was a million miles away."

Nowadays, with the likes of the Chemical Brothers, The Prodigy, Underworld and Orbital enjoying healthy chart positions on a regular basis, the line between underground and overground has become a blurred one. And when you have a name like Leftfield, there are certain standards to maintain.

"That's the trouble about having a name like that; you've got to live up to it the whole time. We should have called ourselves `Mainstream'," Daley laughs.

"But the whole scene has gone from being an underground thing to being the mainstream. Dance music is all over the TV, on adverts, on the intro for Sky TV. Five years ago, nobody knew what it was; it was totally alien to people. Now, even The Six O'Clock News in London sounds like the beginning of Song Of Life. When I first heard it, I couldn't believe it - The Six O'Clock News influenced by rave culture! It made me realise how much our music had infiltrated the mainstream. It's a reality and you have to go with it. The only alternative is to stop making music. People go on about the underground. What is underground nowadays? Two blokes in a field dancing to a car alarm?"

Despite, or perhaps because of, this situation, Leftfield still use some wilfully maverick ploys when it comes to their music. The world's first encounter with new Leftfield material came unannounced and unhyped in a Guinness advertisement: their track Phat Planet was the soundtrack to Jonathan Glazer's striking black-and-white advertisement featuring surfers and horses.

"No-one knew it was us so we were getting an honest reaction from people," Daley explains. "When the advert came on, even a lot of our really close friends were unaware that that was us. We liked that because we wanted people to be objective about it. We did it because it wasn't contrived, you had real people in it, a lot of real surfers from the west coast rather than a bunch of male models. They were trying to do something different with the advert and with the filming. In fact, the music and the film have overtaken the fact that it is a Guinness advert."

Phat Planet is the ideal taster for Rhythm & Stealth, an album which has the trademark intensity and darkness we've come to expect from Daley and Barnes. Their collaborators, too, were carefully chosen.

"Some people were expecting us to bring in loads of celebs but it would have overshadowed the music. Someone like Afrika Bambaataa (seminal New York rapper featured on Afrika Shox) is not that well known, he's not Cliff Richard now is he? We wanted to work with fresh voices, and I think that comes out in the music. Working with Roots Manuva (upcoming London rapper) on Dusted was probably one of the best experiences of my life. It was refreshing to work with someone from the hip-hop fraternity who was so open-minded musically, racially, every way."

More than most, Paul Daley appreciates the value of such a fresh approach. From early runnings on the London club scene through to his involvement with A Man Called Adam and on to Leftfield, he has seen at close quarters many stylistic comings and goings.

"Like, you have people walking around now with mullet haircuts which are supposed to be really trendy - I hated the mullet haircut when it was around the first time and I still do," the ex-hairdresser notes with a loud laugh. "Yes, there are people around the place now doing their own thing but it's only a retake on something which has happened before. It's swings and roundabouts, you get it with music, fashion, art, film, everything, but when you have a generation of people who didn't live it the first time, then it's fresh."

With club culture, though, such change can often be effected by just one record: "In the 1980s, there was a definite difference about underground clubs, especially in London," Daley notes. "It was a bohemian world compared to the straight, ritzy clubs. Now, at the end of the 1990s, they're all virtually the same. But with dance music, a record appears and moves the whole thing along in a new direction. That's why it survives. I know it's a cheesy record but that Stardust record was enormous in that respect." But it's also symbolic of how fast new tastes and fashions circulate. "Thousands go to hear Carl Cox DJ-ing, but they probably don't know half the records he is playing. People go to see him because he is a celebrity, he's on The Big Breakfast. And that's cool, I'm not against that because that's what happens. But we're definitely living in an era where celebrity and hype tend to overshadow the music.

"We still want to make good music and we hope it doesn't matter what we look like. I walked in here today and they didn't have a clue who I was (laughs); they probably thought I was someone trying to blag in to see the MD. I have tea all over my manky T-shirt and I look a right mess but that's the way we are and it shouldn't matter or over-shadow what we do."

Rhythm & Stealth is out now on Hard Hands/Sony