The Myspace effect can be overstated. Arctic Monkeys got so hacked off with it, they began to claim they hadn't even heard of the Murdoch-owned networking site. And it's still not clear who on earth was responsible for Sandi Thom. But when an unsigned band - from St Albans, of all places - racks up 1m downloads on their Myspace minisite and then sells out the 2,000-capacity London Astoria, something is definitely afoot.

It certainly feels that way tonight. The show sold out weeks ago, and although a good chunk of the audience are evicted for underage drinking during the support act, the room is still packed with eager fans who have to get up for school in the morning. Most of them are wearing Enter Shikari rave rings equipped with flashing LEDs, and are crowd-surfing well before their heroes take the stage.

Three ambulances were called to the band's recent Dublin gig, and the state of the pit here suggests that the Leadmill's first-aid kit might be seeing some action too. "Are you lot ready to have it fucking large?" asks 20-year-old singer and sampler Rou Reynolds, as the strobes start flickering and huge drums signal the band's eponymous theme song. In his swimming shorts and urchin haircut, Reynolds leap on the speakers as he orchestrates the band's odd racket.

They call it "post-hardcore". Whatever: it's a tightly knitted, exciting mix of soaring Ibiza synths (which perhaps explains Reynolds' stagewear), Nine Inch Nails-y industrial rock, grrraaagh vocals, occasional ska bounce and the odd Lost Prophetian big melody. The Feast and OK, Time for Plan B are highlights, but whether they will be bothering the charts soon is anyone's guess. On record, and without the mad fans in tow, they would be a less-exciting proposition, but Enter Shikari deserve a life beyond Myspace.

· At Esquires, Bedford, on December 22. Box office: 01234 340120. Then touring.