La Roux, Scala, London

Cracks in a mask of confidence

Their name means "the red", their biggest single was about being bulletproof, and their first hit described going in for the kill.

You'd imagine, then, that La Roux would be a fearsome live prospect, overflowing with Brixtonian energy and the kind of confidence that inspires fashion statements like singer Elly Jackson's trademark arching quiff. In person though, this confidence is superficial both in its physical manifestation, as the bright, primary colours of Jackson's recent outfit at the Mercury Prize awards and tonight's monochrome ensemble, as well as conceptually, with an emotional fragility underlying the bulk of their material. The group's self-titled debut garnered mixed reviews, but commercial success beckoned and with it came mass popularity. Tonight's crowd pushes against the walls of London's packed and overheated Scala.

Running the obligatory 15 minutes late, it's nonetheless to emphatic cheers that opening number "Tigerlily" is received. Flanked by two keyboardists and a percussionist on an electronic drum kit, Jackson looks a little rigid at the start, but soon she's shaking and bending at the hip in time to the beat in a jerky, robotic dance that inspires the few sections of the crowd who have the room to do the same. Luckily, with the unifying force of synth player Emma Drew and Jackson's co-writer Ben Langmaid providing a driving rhythm absent from the recorded LP, Jackson is free to explore all vocal alleyways while her adoring crowd sways and robot-dances with particular enthusiasm for "Fascination", which recalls the Eighties electronica of Depeche Mode and Eurythmics.

La Roux's music is the result of both a strict upbringing at a school Jackson has described as "Nazi" in its approach to discipline and a rebellious period in which the warehouse parties of the capital became the singer's regular haunts. It aches with contrasts, and Jackson's vocal delivery is similarly bipolar, flitting between the coquettish insouciance of closing number "Bulletproof" and the almost teary delicateness of "I'm Not Your Toy".

Despite their youth, La Roux appear blessed with a peculiar wisdom that reinforces much of their material. When Jackson chimes "My reflections are protections/ they will keep me from destruction", the couplet seems an apt reminder of pop's uncomfortable relationship with sincerity. We're reminded that tonight's Elly Jackson is not necessarily the same 21-year-old who has been charming interviewers around the world, nor the diva whose strops have earned her the press nickname "Danny La Roux".

Charmingly, her onstage persona is at once the archetypal pop star, reaching out to touch the outstretched hands of a frenzied front row, and intriguing and aloof, with her gaze often fixed on the middle distance. With the audience well and truly under her spell, her smallest moves, from drinking a bottle of water to trying to help fix a keyboard during one of the evening's few glitches caused by technical issues, solicit waves of adulation.

It's unfortunate to hear so much sampling and some pre-recorded backing vocals at a live gig, but charges of traditional pop vacuity are easily dismissed with a flick of Jackson's hair and the dancing interludes that punctuate tonight's performance.

So where next for La Roux? Having emerged unscathed from the inevitable and unfortunate comparisons to fellow ladies of electropop Lady Gaga and Little Boots, it may well seem like a case of being all dressed up with nowhere to go, since so much of their debut charted the breakdown of a long-term relationship. This week they missed out to fellow young Londoner Speech Debelle in the Mercury Prize, but here's hoping that La Roux's next efforts eclipse those of their ambitious first album.