CLASSICAL MUSIC Ustad Nishat Khan / Ensemble Gilles Binchois QEH, London

There is no record of Pope Gregory the Great ever having met a Sufi mystic, nor any obvious precedent for mixing the chant that bears the Christian saint's name with music of the Islamic sect. The Paris-based Ensemble Gilles Binchois, specialists in medieval vocal music, and ace sitarist Ustad Nishat Khan, welded together the two musical traditions to create a hybrid form of unexpected expressive richness and no little beauty.

For all the New Age associations of sacred chant and eastern music with those elusive states of inner harmony and spiritual serenity, the contemplative side was here overshadowed by the sensual passion of such chants as "Domino illuminatio mea", complete with Khan's sublime, song-like introduction, and the simple, free-flowing polyphonic treatment of "Viderunt omnes". The erotic charge was boosted further by a flamboyant morning raag from northern India, delivered with pulse-raising energy by the charismatic Khan and his anonymous tabla and tambura colleagues, and a solo raag packed with thrilling flourishes, subtle melodic twists and ghostly echoes of notes struck with great force.

The business of uniting Gregorian chant with Indian classical music clearly demanded compromises, with Khan's scope for improvisation reined in by the structure of each chant and the latitude for vocal ornament restricted more by the bounds of good taste than any technical limitations. Purists would likely find the results disappointing, distressing even; while cynics will claim that the cross-cultural marriage was arranged hastily after the success of the Hilliard Ensemble and Jan Garbarek's union, no doubt in the hope of conceiving a "Son of Officium". But to less refined or jaded ears, the blend of antique music highlighted many more points of correspondence than of dissonance, especially so as the two men and two women of the Binchois team inflected each chant with eastern-sounding flourishes and grace notes and Khan largely kept his abundant soloist's ego in check.

Unhappily, the sitarist proved less even-tempered when his young supporting tambura player apparently offered the wrong fixed chord to the singers, forcing a false start to the Alleluia "O virga mediatus" and prompting a level of on-stage stress that ran contrary to the desired effects of the music. Khan's decision to tune the instrument himself for the next number, however necessary, looked ungenerous, as did his body language throughout the remaining numbers, hardly an endorsement for the marketing people who hatched the title "Meeting of Angels" for this concert and its recorded incarnation.

The Ensemble Gilles Binchois, electronically amplified to sound suitably ethereal, restored the focus to the music with an ecstatic account of the Alleluia for Easter Sunday "Pascha nostrum", its complex melody decorated with unrestrained twists and turns and punctuated by contrastingly simple sitar interludes. Elsewhere, the Binchois singers offered traces of the origins of western polyphony, adding droning accompaniments to existing chants and bold traces of eastern colour to several organum-style settings. Any tranquillizing effects offered by this particular meeting of angels were nullified by the sheer emotional strength of one florid organum, a Benedicamus Domino setting, that could have called even the unfaithful to prayer.