Over the past week or two, something extraordinary has been happening in the musical life of London, as performers from as far apart as Morocco and Java have gathered to celebrate the rich musical and mystical traditions of Sufism - and what a celebration it was. Islington's grandiose Union Chapel has witnessed many curious events in its time, but possibly none more remarkable than Friday's culminating concert, when the six participating groups all performed to a packed house of delirious seekers after - well, what? Musical edification? Spiritual enlightenment? A frisson of the exotic? Or perhaps simply a stomping good night out?

Things got off to a rousing start with the irruption into the hall of the Aissawa musicians from Fes, whose 6ft-long trumpets and massed percussion created an irresistibly intoxicating wall of sound. Rhythms were blurred by the church acoustic, but the resonance certainly helped their singing, even if this (like almost everything else in the concert) was excruciatingly over-amplified. The soaring vocals of the Wadali Brothers, from India, also benefited from the immense space, although perhaps, like the other performers, they needed more than a half-hour slot to really get going. In contrast to the characteristic continuous flow of most of the evening's music, the New Ensemble of Jakarta's creations seemed to be informed by a rather westernised, fragmented sensibility - chunks from various Indonesian traditions presented in a sort of dream-like collage - but none the less with some haunting, powerful moments. Egypt's Sheikh Yaseen El Tuhamy and his accompanying munshidin were wonderfully benign in their delivery of typical Sufi songs, mixing images of profane and sacred love.

Percussion, flute and voices, plus zither, lute and rebab, featured in the music of the dervishes from Konya, in Turkey. Curious modes and tunings lent a special flavour to this, but most memorable was the extraordinary rhythmic chanting - like breathing, or the pulse of the heart - heralding the entry of the sombre-cloaked, high-hatted dancers. Cloaks cast off to reveal dazzling robes of white, the dervishes, with an air of trance- like detachment, slipped into their whirling dance, revolving in a strangely disembodied way that was unearthly and solemn in its effect. As they sank down into quiescence, a solo voice, like a muezzin, soared in lonely salute.

After this, the warmth of qawaali singing, with its strong major-key feel, provided a perfect climax to the evening. Mehr and Sher Ali and musicians from Pakistan built up great pyramids of coruscating sound, through which amazing, piercing vocal outbursts cut their way like shafts of lightning. The exhausted but happy audience were worked up again into clapping, swaying participation, until the concert came to an abrupt but satisfying end in the early hours of the morning. Laurence Hughes