Joan as Police Woman, Shepherds Bush Empire, London

From backing musician to arresting performer

At the moment Joan Wasser strides onstage, it's hard to picture her a few years ago, in the shadow of Antony Hegarty and Rufus Wainwright, for whom she was a backing musician. Then and earlier, she was chiefly known by her association with high-profile musicians such as Elton John and Jeff Buckley; she was dating the latter when he drowned in 1997. It was her 2006 debut album Real Life, under the name Joan as Police Woman, that took her to the status of celebrated musician in her own right.

Tonight, as she performs songs from her two alt.soul albums, it is hard to imagine her as anything else – especially when a sizeable crowd of fans masses in the foyer to have their albums signed after the show.

The Connecticut star's sparkling, clingy gown teeters on the gauche side of glamour, striking an image somewhere between classical-performer elegance and showy pop/soul singer. The musicianship of her performance is much the same. Wasser's classical training on violin and piano (and a stint with the Boston University Orchestra) bleeds through her songs, complex in their arrangements and showcasing the sort of multi-octave vocal control rarely heard at a pop concert. It's a point she makes as she tunes her guitar: "At least you know I'm not lip-synching. I was at that Saturday Night Live with Ashlee Simpson? The drummer hit the wrong loop and the song that she sang started again. She started doing this strange dance. These people aren't singers, they're just entertainers."

From anyone else it could sound horribly condescending, but Wasser's easy, unreserved confidence reeled her audience in from the start. She flirts outrageously with the crowd, creating an erotic ambience with her breathy between-song banter, innuendo and revealing lyrics, all held in the right balance between light and serious.

Joan as Police Woman's latest album, To Survive, was written as her mother was losing her battle with cancer, and the subject matter of both her albums spans love, sex, loneliness and Elliott Smith – another musician whose life was cut tragically short. "To America", the single on which she collaborated with Wainwright, was inspired by her mother's suffering, which led her to reflect critically on her country's politics (she performed at a benefit concert for Barack Obama early this year). "While we were on this tour, our country elected the right person. I've been moaning to you about our government and now I don't have to any more," she says, and dedicates the song to "the new Black House" as she launches into its jaunty piano melody.

A seamless move into "Furious" again demonstrates an effortless classical ability for arrangement. Live, Joan as Police Woman's full range of musical styles is heard to best effect. The lounge-jazz feel of her piano-led opener "Honor Wishes" contrasts with the intense, dark tones of "Fire", in which she morphs into grungey rock-star, warm purple-pink lights turning to cool smoky blue, obscuring her face as she plays her mistuned guitar. She also does the intimate solo piano song "To Be Lonely" to captivating perfection. Here, she most resembles her haunting sepia-toned profile picture on the cover of To Survive, singing with raw emotion and not a hint of unwanted sentimentality. Then, when she plays the meditative "Real Life", you can hear the Wainwright touch in its subtle, measured piano and wistful, dreamy, rising vocals.

Her best melodic songs are highlights, too; the duet with Hegarty, "I Defy", might miss his distinctive vocals (though her excellent rhythm section bassist Timo Ellis and drummer Parker Kindred share vocal duties capably), and the brass section is absent, but it is still intoxicating in its beauty.

In "We Don't Own It", dedicated to Elliott Smith, the absence of cello is covered by Ellis, seated as he creates the sound via bass and effects, against Wasser's sparse guitar. "Eternal Flame", sweeping the listener along in its melody and swift-flowing rhythm that mirrors the "oceans, rivers, lakes" of Wasser's octave-spanning vocals, and "Ride", are the night's other melodic gems that single out Joan as Police Woman as an exceptional talent. Those signed CDs could soon be very valuable indeed.