As befits a singer-songwriter in the spring of her career, 27-year-old Alaskan Jewel Kilcher recently sought some career advice from that elder statesman of acoustic melancholy, Neil Young. Young, who has carved a 35-year career from grouchy unpredictability, apparently suggested Kilcher "show her audience no respect at all".

Sage words indeed, but there is not much chance of Kilcher acting on them here. The Festival Hall crowd are perhaps the most painfully earnest audience this side of an evangelist rally.

When Kilcher refuses a shouted request, claiming she has forgotten the song's words, a balding young man clambers on stage brandishing a home-made collection of her lyrics. He holds it aloft while she sings, gazing at her with a look of simpering devotion.

Any sane rock audience would react to such mawkish behaviour by booing and throwing litter at the interloper, but Kilcher's crowd are made of drippier stuff. "Awww," says a woman behind me. "He's sweet."

Drippy they may be, but there are clearly plenty like them: Kilcher has sold over 20m records worldwide.

The first half of the show demonstrates precisely how she reeled them in. Accompanied only by her acoustic guitar, she runs through a set of bedsit folk, polished until it gleams.

Even a cynical observer would admit that Kilcher has a superb voice. It swoops between octaves, recalling Joni Mitchell; builds to a howl and fades to a whisper; piles on the vibrato for lip-quivering effect. The audience greet every song with screams of adoration.

The intimacy and individuality vanish when Kilcher brings on her band. Her voice is submerged in unremarkable AOR glop. It's rock with rounded edges - it could be anyone from Sheryl Crow to the Corrs.

Only the closing Who Will Save Your Soul stands out, courtesy of a loping reggae beat and scat vocal. And when a scat vocal is a highlight rather than an irritating diversion, you have to conclude events have gone seriously awry.

The encore brings the concert full circle: the band are dismissed and Kilcher sings You Were Meant for Me, a sweet acoustic ballad. The audience leave their seats and crowd around the stage, softly singing along. Even Neil Young, you suspect, would be touched.