BBC SO / Knussen, Barbican, London

The BBC Symphony Orchestra was on exceptional form in its Barbican concert last Thursday under Oliver Knussen. Knussen is a large man, but his gestures are small. Monteux seems to be his model, a conductor famous for his tiny beat but also for demonstrating that on the podium less is often more. It was Monteux who between 1911 and 1914 conducted the premieres of some of the most significant scores of the 20th century, not least Stravinsky's Petrushka.

So it was a nice bit of planning to programme a Monteux highlight conducted in a similar fashion. Petrushka opened Knussen's concert, played in the less familiar 1946 revision. Knussen's Petrushka was as though newly minted, the raw and the childish elements of the score heard so immaculately, the dynamics so carefully weighed, the colours so wonderfully varied, the rough and tumble of the fairground preserved. Knussen's take on the score seemed positively filmic: we had no need to see the puppets or the crowds. And perhaps because Knussen himself has written so touchingly for children, he never wanders too far from the story telling.

Mark-Anthony Turnage's viola concerto On Opened Ground was written for Yuri Bashmet and the Cleveland Orchestra and first performed in 2002 - it was Turnage's first commission from an American orchestra. Albeit discretely, Turnage implied at his pre-concert talk that all had not gone well.

Although we were hearing its second performance, one suspects that this was its real premiere. The concerto is in two movements lasting about 25 minutes. The first movement, called "Cadenza and Scherzino", opens with an elaborate cadenza for soloist that moves from gruff motivic phrases - elegantly picked up by smooth string harmonics in the orchestra - to splashy double-stopped chords. During this movement, the soloist rarely ceases playing, but Turnage has provided an exquisitely heard orchestration that never drowns. Even in the "Big and Loud" section, when the brass keens, the soloist emerges unscathed with the instruction: "Warm and intense - lots of bow". As in so much of Turnage's work, dark melancholy is never far from the surface and the colours of the viola are well suited to this mood.

The second movement, "Interrupted Song and Chaconne", is slow, marked "hypnotic" and as the high, intense sound of the soloist enters, the atmosphere is decidedly mournful. Three times, Turnage interrupts with contrasting material, leading to a chaconne that underpins the final section of the work. In Lawrence Power, Turnage has the dream soloist, a performer of immense ability, assured and possessing the emotional imagination to clarify complexity.

As a final bonne bouche, Knussen revelled in Varèse's rarely performed Arcana, a work for massive orchestra. Knussen used a small beat; the volume was astounding; he gave us a small smile.