This was quite a departure. Natacha Atlas has had a colourful, wildly varied career that has involved anything from working with Transglobal Underground to notching up a major pop hit in France, and recording a series of solo albums that have established her reputation for mixing swirling Arabic pop with rap, drum'n'bass and belly-dancing. But tonight she was perched on a stool and surrounded by a small acoustic band half hidden behind their music stands.

The line-up included such Arabic instruments as the oud, the ney flute, and the darbuka hand drum, alongside cello, double bass, piano and acoustic guitar. This may have been yet another new musical experiment for the Anglo-Egyptian singer, but it was, she announced, not uniquea "because the Arab world has been mixing classical styles with jazz and western influences, for far longer than I have". Following in that grand tradition, her set included reworked songs from some of the Arab world's musical heroes - Lebanese diva Fairuz and Egypt's Abdel Halim Hafez.

The arrangements, by pianist Harvey Brough, provided an intriguing mixture of western and Arabic influences, matching cello against oud or drums, but the real surprise was Atlas herself. Singing in such an unexpectedly small venue, she showed that she could put her dance diva repertoire to one side to display a soulful delicacy and subtlety.

Alongside the Arabic classics, she added a distinctive treatment of the traditional Celtic and American folk song Black Is the Colour, an acoustic reworking of her own Hayati Inta and a more thoughtful version of her French hit, Mon Amie la Rose, dedicated to her dying mother. It may not have been the Atlas set that the diners had been expecting (apart, perhaps, from the frantic and over-long drum workout at the end), but it was an impressive transformation.