Well, here's a thing. An Oregon band best known for adopting the Spinal Tap adage "Have a good time all the time" are enchanting an audience old enough to be their disapproving parents. As the Dandy Warhols skate through their emblematic Not if You Were the Last Junkie on Earth, the chorus is belted back by their fiftyish fan club: "Heroin is so passe!" When did this louche foursome, who spent their first three albums treating their bodies like science projects, acquire cross-generational appeal?

Most of the two-hour show is played in supposedly atmospheric semi-darkness, the Dandys silhouettes against backdrops of clouds and trees. It's the old "keep stage dark to impart narcotic wooziness" trick, but what would work in front of a half-cut crowd on Glastonbury's Pyramid Stage is counterproductive in workaday south London. The first few songs, which illustrate the newly-minted synthedelica of current album Welcome to the Monkey House, go down well, but by the half-hour mark, people are shuffling. An hour in, the hum of conversation competes with the music, and only Last Junkie, Bohemian and some spangly selections from the first album pierce the torpor.

But there are interesting things going on in the interaction of Zia McCabe's swishy keyboards (which she plays with her right hand, her left rigidly aloft like a flagpole) and the velvety textures of Courtney Taylor's and Peter Loew's guitars. Taylor also sings, languidly taps a bongo drum and drawls in a "Cockney" accent that makes Madonna seem like she was born within the sound of the Bow bells. With a trumpeter adding nostalgic bleats, there are times when the Dandys epitomise the cooler end of Anglophile indie-rock, whizzing the best bits of the 1960s and 1980s in an electronic blender.

But the new credo - "excess in moderation" - that gives them the stamina to play for two hours seems to have drained them of presence. Ask the school-run mums, who look decidedly less enchanted than they did 90 minutes ago.