The motto of G4, the diet-classical quartet who took second place in the X-Factor television series, is: "All songs are there to be sung." That translates as: no songs are safe from their light-opera attentions, which they honed as buskers after leaving the Guildhall school. If you can weld a falsetto crescendo onto it, whether it's Bohemian Rhapsody or Britney's Hit Me Baby, G4 are having it. That would have been fair enough, had they stuck to their busking career. Surely, though, this was never meant to be happening at the Albert Hall. Yet it is. The group sold 300,000 copies of their debut album in one week back in March.

When the foursome themselves appear, tentative and stiff in their lounge suits (the first of five - five! - costume changes), they're greeted by squeaks of lady-lust that would flatter Justin Timberlake. But why? The secret of their allure is never satisfactorily divulged during the show. If anything, their starchy banter should have the crowd pining for their foreign rivals, Il Divo, who at least emanate a whiff of swarthy badness. Instead, an entire room is going gently nutty for four chunks of Home Counties posh whose collective sex factor is nil.

It's easier to fathom the popularity of their music, which tonight is derived from both the debut album and the next one. (Yes, there's already a next one in the pipeline.) G4 operate from the canny standpoint that most people would like opera if they knew the words and it weren't sung in Italian, and they're right. Pop staples make up 90% of the show, ranging from Bowie's Life on Mars to Radiohead's Creep, and the pashminas are in raptures at hearing familiar lyrics rendered in soaring tenors. Thus primed, they wave along to a bit of real opera, featuring guest Lesley Garrett, and G4 exchange glances. Are they nervous, or just unable to believe their luck?

· At the Regent, Ipswich, (01473 433100) tomorrow. Then touring