Ben Thapa has just finished a gruelling hour and a half with his personal trainer when I speak to him and he's exhausted. But as G4 is about to embark on a huge national tour, fitness is the key, so the boys are all knuckling under.

"After a month with the personal trainer we are finally starting to see the results," the 23-year-old says groaning, "but it's really hard work. I'm starting to feel the benefits though considering a month ago I couldn't even do a press up, " he laughs.

Add stylist, voice coach, band, managers and roadies to the list and you begin to realise that the G4 tour is a small moving empire, coming to Oxford on June 24.

But then the success of Jon, Matt, Michael and Ben has been so phenomenal in the past year it's easy to understand why their managers are pushing the boat out. Ben says: "Looking the part is partly to do with it but physical fitness is also important because touring is very physically demanding."

Luckily all the boys knew each other first before they came to fame as the 'classical' novelty group on TV's X Factor, being pipped to the post by Steve Brookstein, who has since sunk without a trace.

"It really is a happy coincidence that four mates started a group for the summer and were all there for each other when it took off. But in the two months of the X Factor we got to know each other much better than we had at college," Ben says.

All together at the Guildhall School Of Music and Drama, the boys used to busk to earn extra cash, but had planned to go their separate ways by the summer. "We tried to busk on the Tube, but they turned us down because they thought four of us would be a fire hazard," Ben remembers. "So we would busk in Covent Garden or outside the Tate. We made over £600 in three hours once," he adds, "the money paid for a few bills and it was a good laugh."

At the last minute, they read about the X Factor auditions and all went along, not expecting anything to happen. "We really had no expectations," Ben says, but their fate was sealed that day and after coming runners up, record companies were fighting to sign them and one can now see why. G4's first album went platinum, topping the charts for weeks, featuring the now infamous single, Bohemian Rhapsody/Everybody Hurts.

Their success is a mix of many things, talent, finding a gap in the market and managing to bridge the wide gap between classical and pop. But are they happy in both camps or do both genres look down on them? "It's strange," Ben says, "because while Classic FM do a lot of things with us, so do CD:UK, so we do have a broad appeal as a group and we have evolved as the show goes on because we have been happy to take other people's opinions on board."

Usually suited and booted, G4 cuts a swathe through the usual rock image. So is there anything they've refused to wear? "We used to have to stylise ourselves and would generally just wear suits, so it's nice to have someone with more experience and ideas dressing us, especially as we are all sorts of shapes and sizes," Ben says. "But there is one part of the show where we perform some Beach Boys songs and we've got matching Hawaiian shirts which might be a tad embarrassing because it's definitely not the sort of stuff I'd normally wear," he laughs.

The four lads are definitely level-headed about their new-found fame and have devised ways to keep themselves sane. "We used to live together, but now we've all got separate flats, albeit three of us in the same block in London," Ben explains. "We worked out that we spend more time together than any partner or flat-mate, and if anything we spent too much time together, so sharing an apartment as well would drive us and each other nuts."

The tour is a watershed for the band. They did a couple of gigs with Westlife and then with the X Factor arena tour, but this will be the first time on their own. "It will be very different, so we are really looking after our voices because, without them, we wouldn't have a career, hence the vocal coach. But there's a good vibe on the tour bus and Voices 4 Soul are coming with us," Ben says.

Even so, it's hardly going to be rocking, is it?

"Well, our fans are everyone from children to the elderly," Ben says, "but we do get a few beautiful women too," he adds shyly, "and to be honest all that is still slightly surreal."