Cassandra Wilson, Royal Festival Hall, London

You get the feeling that the Mississippi-born jazz and blues vocalist Cassandra Wilson is never more at home than when she's on stage. For her London show she has brought a rug with her and had it laid out across the front of the stage. It's not long before she's kicked off her shoes and is padding around barefoot as if relaxing in the comfort of her own home. Dressed in flowing white – peasant-girl chic has never looked so classy – she skips, slides and shimmies about the stage; from time to time letting out a girlish giggle. There's a mischievous streak, too: at one point she gently mocks the serious look on one punter's face. "There's a word for an expression like that," she laughs, lifting her eyebrows, sticking out her bottom lip in imitation.

Over the past 15 years Wilson has been hailed by excitable jazz writers as the next Betty Carter and the new Nina Simone, lofty comparisons that would kill any other artist's career stone dead. There's certainly a gap in the market, however, with Wilson's honey-voiced contemporaries Erykah Badu and Jill Scott preferring to travel the hip hop and nu-soul route.

Wilson has been criticised for an eclectic repertoire that has often strayed outside jazz. Lately she has immersed herself in the sound of American roots music. This year's Belly of the Sun album, recorded in a converted train station in Mississippi, contains covers of Bob Dylan and Robbie Robertson, alongside the blues and gospel standards. In a spirit of defiance, the singer draws on much of Belly of the Sun tonight, from the languorous "Darkness on the Delta" and the James Taylor-penned "Only A Dream In Rio" to Fred McDowell's "You Gotta Move" and a rare Wilson original, "Justice", a slightly wordy song about reparations for slavery.

We're treated to a raucous cover of "A Foggy Day In London Town" and Robert Johnson's "Hot Tamales". Grinning from ear to ear, Wilson seems more at ease with these upbeat tracks. By contrast, her version of Jimmy Webb's "Wichita Lineman" during the encore is lumbering and slow.

There's no getting away from the power of Wilson's voice. One minute she is all smoky intimacy – she often sings so quietly that the whole audience seems to hold its breath lest they disturb her concentration – the next she is brash and bawdy-sounding. For much of the evening, it's the sound of a woman having one hell of a time.