This stunning performance from Amy Winehouse could not have come at a better time for her, or indeed for her long-suffering fans. The singer has developed a reputation for cancelling shows through "exhaustion" or "illness", only to be spotted later, apparently engaged in a one-woman mission to keep north London's pubs and off-licences in business.

Nor did the singer cover herself in glory at her outing last week at the Eden Project, if reports of drunken gibberings, forgotten lyrics and spitting into the crowd are anything to go by.

But at the ICA last night, as part of the ongoing iTunes festival, the 23-year-old provided a spectacular reminder of exactly why she was declared best British female artist at this year's Brit Awards, and why she is the bookies' favourite to scoop this year's coveted Mercury Music Prize.

Winehouse appeared on stage 50 minutes late, flanked by a nine-piece band decked out in slick black suits that were in keeping with the soulful Sixties vibe of her acclaimed album, Back To Black.

Her tiny physique clad in a black and white vintage dress the straps of which fell down repeatedly throughout the show, Winehouse achieved instant forgiveness for her poor timekeeping as soon as she opened her mouth. Tears Dry On Their Own, which made good use of the band's brass section, showed off Winehouse's breathtaking voice.

Live, even more so than on CD, Winehouse's voice was truly soulful, not only because of its similarity to the sounds of the black soul singers of the Sixties, but also because of its effortless emotional expression, giving the impression that with the aid of a couple of drinks, Winehouse was offering us a genuine glimpse into her troubled soul.

Pop stars and intoxicants have always gone together, leading some to imagine a causal connection between drunkenness and musical success. In my view, the opposite is true. Drink and drugs have ruined more music, and more musicians, than they have ever enhanced.

But while it would be wrong to praise or trivialise Winehouse's well-documented problem, it has to be admitted that her mild intoxication last night added something to the performance. Her sultry, glassy-eyed glare and the tipsy sexiness of her movements on the Sixties-style Me And Mr Jones gave her an intensity and air of abandon that would have been unthinkable had she been completely sober.

A dramatic change of pace came in the form of an excellent cover version of You're Wondering Now by The Specials, which saw hilarious ska dancing break out among Winehouse and her band.

But it was last October's hit, Rehab, that the crowd were screaming for. She finally belted it out during the encore. A bass saxophone created a dramatic, Motown-ish backdrop as the crowd sang along with the chorus: "They tried to make me go to rehab/But I said no, no, no." These lyrics encapsulate both the feistiness and honesty that make Winehouse a great lyricist, and also the self-destructive streak that could yet scupper her career.