Classical: Birtwistle Series Queen Elizabeth Hall, London

The trouble with retrospectives is that artists still alive fear they may be dead. Harrison Birtwistle admitted as much during rather soft- edged questioning from Face to Face chief Jeremy Isaacs in a pre-concert "confessional", where the single spotlight suggested Birtwistle as possible God or possible convict. A God seems more likely these post-Panic days, if concert halls packed to the rafters for this month-long look at his work is anything to go by. But was it loss of nerve or evidence of an increasingly commercially opportunistic management at the South Bank that mystifyingly shoved a quart into a pint pot?

Earlier Birtwistle concerts in the Purcell Room by Lontano and the Endymion Ensemble left not only the public stifled, but the music too, for if there is one overriding characteristic about all Birtwistle's music, it's the space both physical and psychological that it requires. Birtwistle, even as miniaturist, in so exquisite a work as La Plage (1972), which was given an intensely haunting performance by the clarinets of Lontano with Sarah Leonard, needs room to breath.

If the spectacular revival of The Mask of Orpheus attracted every known Birtwistle follower in the past 30 years, they all pitched up again (not a heckler in sight) for the premiere of his latest work, Slow Frieze, in Friday's concert given by the London Sinfonietta. This is the sixth piece Birtwistle has written for the London Sinfonietta and in a deft bit of programming, the earliest work Verses for Ensembles (1969) was featured as well. The nature of these "Retrospectives" is to get into some kind of perspective what an artist has been up to, so the juxtapositioning of these two chamber works was illuminating indeed. The sheer stylistic consistency across the years is wholly remarkable: the layers move like tectonic plates; the pitches scream from on high; bleakness, stillness, melancholy vie with ferocious, elemental eruptions; the pulse is pervasive. But whereas Verses for Ensembles, here given a scintillating performance energised by Markus Stenz (how playing standards have advanced in 30 years!), is clear and concise in its building blocks, the newer work seems undercharacterised, inhabiting Birtwistle's stylistic world but somehow having little to say. Certainly by comparison with his notorious Panic, Slow Frieze seems to be something of a retreat. Written for Joanna MacGregor, presumably as a thank-you present for stepping into the breach to save the premiere of Birtwistle's other piano concerto, Antiphonies, Slow Frieze is an ensemble work where the piano moves between the various free-standing layers without serious treatment as a concertante soloist.

An intriguing aspect of the score is the freedom offered the four wind players to choose melodic fragments at moments triggered by the percussion, so introducing an element of controlled improvisation. But on a single hearing no judgement can be made about the aural significance of this approach - too bad a second run was not on offer.

n The Birtwistle series continues to 4 May. The Arditti String Quartet play the premiere of 'Pulse Shadows' tonight at 7.45pm, QEH, London SE1. Booking: 0171-960 4242

ANNETTE MORREAU