Even in an era when R&B lays a strong claim to being the most groundbreaking and unpredictable genre in the world of pop, certain rules still apply. Female R&B singers are meant to be designer-clad, coiffured to within an inch of their lives, and surrounded by a retinue of make-up artists and stylists that an 18th-century monarch would consider excessive.

No matter how outlandish the music, the female R&B diva's lyrics should stick rigidly to time-worn themes: failed relationships, female empowerment and the ghastliness of men.

In this world, Kelis Rogers cuts a curious and refreshing figure. She famously eschews a stylist in favour of her own, bizarre taste in clothes. Tonight, she bounds on stage wearing a nightmarish ensemble of tie-dyed purple dress, bright red trainers and black socks.

Her lyrics are equally strange, even disturbing. Kaleidoscope, her 1999 debut album, complemented the disjointed funk of production duo the Neptunes with fantasies of space travel and murderous revenge: "I'll set your truck to flames and watch it blow up," she coos sweetly on tonight's first encore, Caught Out There.

Live, the gulf between Rogers and mainstream R&B is even more apparent. On opener Perfect Day, her backing band - all female except the drummer - transform the stuttering rhythms and studio effects of her records, matching Rogers's powerful voice with a raucous, guitar-laden noise somewhere between Funkadelic's early-1970s psychedelic soul and brooding rock.

New single Young, Fresh 'n' New finds her singing over a menacing backdrop of squealing car alarms.

On stage, Rogers is as intriguing as her music. She suddenly does the splits, performs an impromptu cover of the Eurythmics' Sweet Dreams, bemoans her recent support slot with U2 ("There's nothing in the world like performing to people who actually want to hear you," she notes wryly), and encourages a hapless audience volunteer to bump and grind with her. His visibly unimpressed girlfriend glowers from the back of the stage.

Before her final encore Rogers indulges in a lengthy monologue about the redemptive, healing power of music. It's the sort of display of sentiment most R&B singers would use to introduce a gospel medley or a syrupy soul classic.

Rogers finishes her speech, thanks the audience and launches into a demented cover of Nirvana's Smells Like Teen Spirit, anomalous to the last.