At five minutes to midnight, two stiletto-booted teenage girls were scurrying toward Brixton Academy, clutching each other's hands, as if Nonentity from Pop Idol awaited on the other side of the door. The surprising focus of their excitement, and that of scores of other adolescent-looking females, was Groove Armada - a teacherly chill-out duo for whom the term "Another cup of tea, gentlemen?" could have been coined.

Apparently, this happens every time the fleet is in. Dates promptly sell out (three in Brixton's case), and Andy Cato and Tom Findlay - who met in Cambridge while jazz trombonist Cato was studying there - preside over roomfuls of fans who look as if their last gig was the Smash Hits Pollwinners' Tour. It certainly makes for a more interactive experience than the usual dance show, though the fundamental question - why? - isn't easy to answer.

Two stabs: first, their trombone-led Ibiza hit At the River is so provocative that the prospect of seeing Cato manhandle his instrument while playing it live is enough to shift tickets. (Sadly, it doesn't happen often enough - he spends the rest of the time looming over a midget keyboard at the back.)

Second, they have a pop sensibility that dominates when staging their show. Historically, dance duos are sleep-inducing live, staticky video backdrops notwithstanding. Groove Armada, though, recognise the need for new thrills around every corner, and incorporate the mandatory widdly-widdly graphics into something much more arousing.

Thus Cato and Findlay weren't happy to just feature living history in the form of 1960s folkie Richie Havens, whose slouchy Little by Little and Going Back to My Roots electrified every pierced bellybutton in the house - they spiced every number with such surprises. The anthemic house tune Final Shakedown, from current album Lovebox, was given double oomph by live ragga vocals from Red Rat and a video of a muscular woman in an Afro whose dancing synchronised with Rat's mad-headed delivery. At 1am, this somehow just worked.

So, a few songs later, did a guest slot from Valerie M, an R&B waif whose belting chimed with Easy's Italian-house groove. As the party reached a heaving peak, the teeny fans jerked ecstatically - and unlikely pop idols Cato and Findlay exchanged wondering thumbs-ups.