The Moldy Peaches, University of London Union, London

Anyone who thought themselves familiar with the shabby but endearing work of the Moldy Peaches, scions of New York's long-running "anti-folk" scene – which basically consists of various buddies running around the city and watching each other perform in bars – was in for a shock tonight. For Adam Green and his one-time babysitter Kimya Dawson, best loved for their witty, shambolic acoustic numbers, have mutated into scary rock beasts. No longer entirely reliant on their followers' loyalty, the duo are now backed by a potent four-piece band, transmogrifying their back catalogue into something bearing a strong resemblance to music that might be played on the radio.

The thrill can only be compared to the shock that greeted Bob Dylan's first electric shows circa 1965. Sort of. All right, so Dylan wasn't wearing a bear head, a comedy "ape-ron" (a plastic apron with an ape's torso printed on it) and a cape with a schwa and crossbones on the back like Dawson, nor even the Pied Piper's hat favoured by Green. And his backing band didn't consist of a rhythm player in a unicorn helmet, a drummer with an eyepatch (actually, it might have), a bassist dressed as a classic French mime and a lead guitarist in a tiara and baseball umpire's shirt.

But the sheer surprise of the Peaches cracking into the immortal "Downloading Porn With Davo" with a solid backbeat can't be overestimated. The place erupts. No one shouts "Judas", though one besotted soul yells "I want your cubs!".

It's great. Once sketchy though melodic songs such as "Lazy Confessions" and the lovely, weary "Jorge Regula" simply swing, while "Greyhound Bus" and, especially, the louche "I Forgot" are straight-out rock. Best of all are the singalongs. The audience seems to know every filthy word of "Steak For Chicken", while the formerly shambling "Lucky Number Nine" and "Anyone Else But You" are similarly echoed.

Being the Peaches, it doesn't go entirely smoothly. Kimya invites a young man with a triangular blond hairstyle up from the crowd to duet on her heartbreaking "Nothing Came Out", while a peeved-looking Green and a guitarist who decides to drop in a horrid Clapton-esque solo do their best to drive him away. (Though to be fair, this does appear to be a planned part of the show.) By the set's conclusion, the ecstatically idiotic "Who's Got The Crack?", Dawson's wild blue afro is revealed and the bassist is no longer Marcel Marceau, but a lost member of the New York Dolls.

I can't emphasise just how entertaining this hour was. The Peaches are rapidly closing in on their obvious influences (Velvets, Violent Femmes), without losing any of their chaotic charm. Ridiculous and cool, this is a show worth seeing.