George Benjamin, 50, London Sinfonietta

George Benjamin turned fifty last week. He's been composing since he was 7, seated at his first piano, improvising the music he heard in his imagination. The Queen Elizabeth Hall was packed with composers, conductors, and musicians for the London Sinfonietta George Benjamin at Fifty tribute, but in many ways, the measure of his stature was seeing him completely alone, playing his Piano Figures (2004). Benjamin's now one of the world's greats, but this connected him to the instrospective boy he was long ago, embarking on a voyage of discovery.

Piano Figures is a series of ten miniatures each built around a mood growing from a simple motivic cell. As in many things in life, "simple" doesn't mean "easy". These pieces don't demand extreme virtuosic technique, but they do challenge the mind. Each vignette builds on a mood or image ("Spell", "In the mirror", "Whirling") but moves on swiftly without exhausting the possibilities. While this isn't a showcase, it's valuable because it turns the player back onto himself, to think and dream, just as Benjamin started out all those years ago.

That sense of rapt listening comes through in Viola, viola (1999). This time, the contemplative dialogue is between Paul Silverthorne and Eniko Magyar. This is music about listening, as well as about making sound: intelligent listening is an underrated skill. Themes bounce between each player, the balance constantly shifting. Long, exploratory lines, countered by affirmative semi-staccato, a pulse connecting, then gracefully receding. Matthias Sperling and Rachel Krische have created a ballet Duet, duet, around Viola, viola. It seemed very sensitive to the flow of the music. At one point the dancers freeze mid air, arms and bodies stretched without touching. They hold the position for a brief moment, then the pulse changes and they move onwards. This is such thoughtful, contemplative music that it needs concentration, so I ended up listening to Silverthorne and Magyar. Fortunately, the dancing was filmed by BBC Radio 3 (which does podcasts), so there will be opportunities to listen and watch again.

Benjamin's At First Light, was written when he was only 22, after the success of Ringed by the Flat Horizon. It was inspired by J M W Turner's Norham Castle at Sunrise, pictured here. Cue for wavering colours and impressionistic effects showing Benjamin's debt to Messiaen, and to Messiaen's hero Debussy. As Benjamin says, the idea was to create music that shows how objects can be formed in "punctuated, clearly defined phrase", but then "melted into a flowing, nebulous continuum of sound".

It's imaginative, more original than the slightly earlier A Mind of Winter, another landscape in sound depicting a winter scene in Wallace Stevens's The Snow Man. Claire Booth sang the vocal part well, but even she couldn't make this piece feel that, as music for voice, it isn't little more than relatively straightforward orchestral song, albeit in a modern style. Still, it's worth hearing to show how far Benjamin has changed and learned from the past. His opera Into the Little Hill is a masterpiece where he's at last achieved his potential as composer for voice. I was one of the lucky ones who heard it in full at the Linbury Studio (please see HERE) Get the CD and get tickets at Aldeburgh and the Almeida this summer.

The London Sinfonietta showed their true colurs in Palimpsests (1999-2002). Such vibrant, animated playing! Such energy and sense of purpose, even though the directions are often wayward, reflecting the initial concept of "palimpsests", medieval documents where different layers of writing are superimposed, often at contrary angles. Like Viola, viola, there are double elements, but here they co-exist rather than communicate. One element is defined by lively polyphony, four flutes and four clarinets acting as "voices". The second element is unusual too, eight double basses and eight violins/violas - no cellos. Three harps, plucked like giant celli. Thundering brass, led by high trumpet, a cataclysmic rolling rumble.

The trajectory and sense of form in Palimpsests reminds me of Boulez, who premiered this work and to whom it is dedicated. Because there's so much nonsense about modern music, the energy and almost organic vivacity of Boulez's music is often overlooked. As Benjamin said in his pre-performance talk with Julian Anderson, Boulez's music is underrated. The talk was good, overthrowing some miscomprehensions, like the idea that spectralism derives from Sibelius (Alex Ross). Messiaen was much too nice a guy to roll in his grave. More likely, he's chuckling, up there in Heaven.

Listen to this programme on 13th Feb on the BBC Radio 3 website (see "Hear and Now") , online and on demand for a week. Sound samples HERE on the London Sinfonietta website.