MUSIC / Arditti String Qt / Claude Helffer - Purcell Room, London SE1

Potted plants and a packed hall: could this be a Xenakis concert? Specially chosen spiky plants, said a South Bank manager; but then Xenakis's music possesses elemental qualities that have always had the potential to speak more directly to a wider public than the tortured sophistications of other senior avant-garde composers. With seven short, ferocious pieces on the programme, the temperature started high and rose steadily.

It's probably all in a day's work to the Arditti, who have recorded everything here. All the same, as a celebration of music at its expressive extreme (as well as of Xenakis at the age of 70), this takes some matching. For some composers' music the Arditti's high-powered intensity is too relentless; not here, neither in the rage and unlikely wit of Tetras, nor in the solo virtuosity of the quartet's cellist Rohan de Saram in Kottos, which roared out unseen from behind a barrage of sheet music.

In the quintet, Akea - which the programme called Ikea, no doubt on the grounds that anybody can screw it up - the string players were joined by the veteran pianist Claude Helffer. His solo performance of Evryali was the evening's highlight, a flamboyant investigation of the keyboard with amazing powers of maintaining momentum. A recent quartet piece, Tetora, seemed relatively plain and dogged - well back from the expressive edge. Otherwise this was a vindication of a great original whose compulsive energy refuses to age.