Maverick improviser Matthew Bourne and London Sinfonietta’s reliable principal players created an extraordinary concert in this second of the Sinfonietta’s Written/UnWritten series. Despite the harmonics and echoes behind a diverse collection of twentieth-century pieces and irreverent improvisations, few risks were taken by anyone other than Bourne, but the result was an impressive and often hypnotic series of the most carefully crafted contemporary classical music of the last fifty years.

The programme consisted of works by Iannis Xenakis and Kaikhosru Sorabji, Lucio Berio and Helmut Lachenmann. This was an evening concerned with the most cutting-edge musical explorers of the last half-century, stopping well short of the obscurity of Stockhausen. With tone clusters and experimental improvisation aplenty, we were occasionally transported into some very special musical shadowlands of harmonics, resonance and artistic excellence, aided greatly by the exceptional acoustic of King’s Place’s Hall One.

Xenakis’ opening Rebonds A was written in 1986 but possesses a timeless curiosity as it spans a wide, if unspecified, range of drum pitches. The effect was of great pendulums of sound that crossed the sonic and rhythmic spectrum in waves and achieved great diversity of dynamics. Limiting the percussion to skinned drums – 2 bongos, 3 tom-toms and 2 bass drums – created a surprisingly soft-edged timbre for a piece composed of sharp, violent extremes of quiet and loud. This was a riveting performance, smoothly executed by David Hockings.

Next came a work by one of the godfathers of contemporary music, Luciano Berio. The seventh of the fourteen Sequenzas he composed between 1958 and 2002, for solo oboe, came across as rigid and grating compared to Rebonds A. Gareth Hulse performed its technical oddities well enough, but the excrutiating grinding sounds his oboe produced, as well as the irksome ‘B’ drone from offstage, were disconcerting and uninspiring. In this context, the single oboe playing against a monophonic pedal apparently represents the continuum of musical development from past to future. But on the evidence of this performance, this concept is effective in theory but unpleasant to listen to. We then heard Kaikhusru Sorabji’s Fantasiettina Atemica. This has had only two other known performances and it is easy to see why. The flute and clarinet swim under the oboe in a shapeless musical gesture that ironically suffered from the lack of a clear theme. Again, the London Sinfonietta players (Hockings, Hulse, flautist Karen Jones, clarinettist Timothy Lines) equipped themselves admirably but there are much better pieces of Berio than this.

Matthew Bourne’s solo piano playing was the much-anticipated pre-interval thriller. ­­­33-year-old Bourne loves to be the centre of attention; he strolled onto the stage with a casual ‘alright?’ and seemed determined to flaunt every rule of performance etiquette. With unkempt beard, bare feet and patched trousers, to describe him as scruffy would be an understatement. Fortunately for Bourne and the audience, there is nothing so ragged about his piano playing. Stirring, virtuosic and often unbelievably pretentious, he stormed through his first improvisation with every note sounding deliberate and precise. Improvisation this may have been, but the four mood sections of his piece had finely tuned characters of their own and demonstrated that Bourne is a supreme technician. Sometimes he repeatedly hit into dissonant chords (which would make any piano tuner squirm) and sometimes would move with lightning speed between sequences on keyboard and the inner strings of the Steinway in Hall One. When he let his fingers fly into impossibly intricate freestyle passages his confidence and skill seemed unsurpassed.

On returning from the interval, we were greeted by a second piece of Xenakis, the impressively-named Charisma. Fittingly, the piece does have a likeable musical personality, consciously rejecting serialism in favour of probing explorations of overtones, blocks of harmonics and spine-tingling special effects by cellist Oliver Coates and Bourne at the piano. The opening reference to Bizet’s Habanera from Carmen was testament to how well the programme showcased classic compositional techniques; it was such cross-referencing, experimentation with form and repetition that made the evening so fascinating. It was refreshing to see a genuine exploration of the building blocking of modern music in a setting less populist than the Barbican’s three-day Reverberations tribute to Steve Reich in May. The London Sinfonietta players were quietly confident with the technical demands imposed by the wide range of styles in Helmut Lachenmann's Kinderspiel, which plays with the conventions of harmony and instrumental technique. But there was no escaping the fact Bourne and Coates were most impressive, with their energetic mastery of piano and 'cello respectively and shared comfort with improvisation.

However, the Sinfonietta players’ unfamiliarity with the freedom of this style was a drawback when the group came together for the final collaborative piece. Although ‘created between Bourne and the London Sinfonietta’, the piece was clearly of Bourne’s writing. And as Bourne coaxed loud harmonic echoes out of the piano with repeated tone clusters, the performance reached a stunning climax. His sensitivity to noise, pitch, harmony and structure was the highlight of a piece; it moved between emotions by repeating sonic effects and motifs with gradually metamorphosizing emotions, ending in contemplation as if feeling around harmony itself. The warmth and emotion achieved here made minimalist and academic jazz seem cold. It is a sign of contemporary music’s perceived inaccessibility that few ensembles feel the confidence to devote entire concerts to any composers whose work was played tonight. They should be reassured however; in this second Written/Unwritten concert the notes and the spaces in-between were definitely in the right place.