Most pop songwriters for hire use their vocation as a means of stepping gracefully away from the limelight - they are often former stars, still capable of coming up with hits, but too old or sensible to spend their lives being screamed at by pubescent hoards. Few would be interested in using their background success in the pop world to relaunch their career as a performer. Fewer still would be interested in using their background success in the pop world to launch a career as a folk singer.

And yet here is Iceland's Emiliana Torrini, last seen collecting an Ivor Novello Award for co-authoring Kylie Minogue's Slow, on stage in a diaphanous smock, accompanied only by a fingerpicking guitarist and singing fragile, lilting songs about being a fisherman's woman. At the very least, you would have to call it an unforseen career shift.

On the evidence of her brief set supporting Woodstock-era hero Richie Havens, however, the unexpected comes as standard with Torrini. Her voice is soft, and the music is informed by the more whimsical end of the early-1970s acid-folk movement, whence ladies in smocks sang about lily-ponds, but Torrini's lyrics are startlingly robust. Quite a lot of songs seem to be about what a handful she is when she's had a few, not a topic addressed in the work of forebears such as Mellow Candle. "I know I'm bad to jump on you like this," she sings on Sunny Road.

Supporting a venerable legend with music so subtle should theoretically be a tough call, but so should covering Next Time Around, a song by English folk's late grande dame, Sandy Denny: Torrini is assured enough to pull both off. Between lines, she sways away from the microphone, eyes closed, head tilted backwards, mouth fixed in a beatific smile, as if in the throes of an overwhelming, but not entirely unpleasant, drug experience. The audience seem scarcely less enraptured, and understandably so: in every sense, this is an unexpected delight.