Sibongile Khumalo is a singer with an extraordinary range of skills and styles. She's a distinguished classical mezzo soprano, praised for her interpretation of anything from Verdi's Requiem to Carmen, but also the one-time star in a series of South African musicals, a musical academic with a string of degrees, a fine exponent of township styles, and an experimental jazz singer. She has provided a sophisticated musical backing for such major political events as Mandela's inauguration as president in 1994, and has been seen here working with other singers in the Women of Africa Project.

Now, at long last, she had her first major show as a headliner in London - and it turned out to be a disappointment, not because her singing was sub-standard, but because there wasn't enough of it. An impressive, stately lady, she was followed on stage by a younger "special guest", Gloria Bosman, who joined her in an impressive jazz workout in which Khumalo demonstrated quite astonishing speed, clarity and control. She then switched from scat singing to a demonstration of her role as a classical diva. This was followed with a slinky, breathy ballad, before Khumalo invited Bosman back on stage to take over.

Bosman is a good, sturdy jazz singer and soul balladeer, but it was not her the audience had come to hear. When Khumalo did reappear she performed an odd choice of songs, with strong South African material by the likes of Abdullah Ibrahim and Moses Molelekwa set against a jazz-funk treatment of My Favourite Things from The Sound of Music.

There were some fine jazz workouts among all this, including a delicate experimental duet with Bosman, but Khumalo had been over-generous in giving away her time on stage. At the end, she and Bosman were joined by the massed ranks of the Women of Mambazo, who had opened the show.

Very much a spin-off project from the best-selling Ladysmith Black Mambazo, the group were founded by Nellie Tshabalala, the wife of Ladysmith's leader, Joseph Tshabalala. He now acts as their musical director and joined them on stage here, along with other male singers, clearly finding it hard not to dominate the proceedings. The result was predictable. Stirring and enthusiastic unaccompanied harmony work was matched with demonstrations of Zulu dance, but without the well-drilled slickness and delicacy of the Ladysmith team.