The work of Sir Harrison Birtwistle isn't necessarily the sunniest music in the world, and coming into the Queen Elizabeth Hall last night for a serious-minded evening of discussion and performances of his intricate, modernist-style music by the London Sinfonietta, I confess to having felt a little reluctant to be leaving behind the sweltering heat of the South Bank. But what was offered up was such an excellent presentation of Birtwistle's music that all thoughts of sun, ice-cream and shorts were left behind, as I became engrossed in learning about and experiencing the composer and his works.

The composer was joined, in the corner of the stage, by music journalist Tom Service, who led the discussion with an admirably clear emphasis on the music. There was no 'Where did you grow up' here, but rather a sincere desire to learn about the compositional process and the structure of Birtwistle's pieces, aided at times by judiciously selected extracts played by the Sinfonietta. The composer himself was a witty and informative participant, if at times a reluctant one - 'I don't want it to become like a music appreciation class', he said at one point. It kind of was like that, but it was fine, as there was much to appreciate in the music.

As a music reviewer, I've found that there are certain terms that always end up being written about certain composers, to the extent that I go out of my way to try and avoid them when writing about their music for fear of slipping into cliché. With Schubert it's 'lyrical'; with Wagner it's 'huge'; and with Shostakovich it's 'Stalin'. Birtwistle has two such words – 'ritual' and 'layers' – and if there is one thing to criticise about the discussion, it's that it mainly consisted of these two pretty familiar Birtwistle tropes getting a thorough workout. But it was still fascinating to hear first-hand about just how very ritualistic a piece like Cortege (2007) is meant to be: ten of the fourteen players take it in turns to come to the front of the stage and 'make an offering', as Birtwistle put it himself, of a short solo.

At the end of Cortege, the flautist (Sinfonietta stalwart Michael Cox last night) approaches each of the other soloists individually and, by way of short, conversational exchanges, summons them to stand. Once all are upright, there is a short coda, whose odd, static repeated notes stand in contrast to the denser polyphonic textures of the rest of the work. It's a reminder that while this is a ceremony of sorts, it's not going anywhere in particular, and the conclusion is as mysterious as the journey there.

The 'layers' part of the discussion focused on Birtwistle's classic Sinfonietta composition Carmen Arcadiae Mechanicae Perpetuum, and we were presented with an analysis of the first six bars of the piece that went through their rhythmic and melodic components, explaining how Birtwistle 'layers' these on top of one another to create a dense (but bouncy) hyper-ostinato patterning. While the Sinfonietta were on excellent form all night, this performance in particular had a real sparkle to it, and David Atherton clearly relished the task of conducting his ensemble through the work.

Five Distances for 5 Instruments is Birtwistle's take on the wind quintet, and again the discussion was a useful introduction to the performance, highlighting how much care Birtwistle had taken to characterise the instruments appropriately. In light of the discussion, the performance became an elemental statement on the differences and similarities between the five divergent instruments which make up this allegedly homogenous group. The players were on great form, with Michael Cox shining brightly in the flute's high flourishes and Michael Thompson anchoring things with strong, gnomic horn playing.

The evening concluded with the UK première of In Broken Images, a large-scale work which premièred in Milan last year. While no radical stylistic departure, this is Birtwistle at his consistent best, a little freer than in Carmen Arcadiae Mechanicae Perpetuum (abbreviating it to 'CAMP' seems wrong) but with the same sense of mechanical dramatic thrust. It also contains what is surely a tribute to Psycho, featuring a succession of thrilling, hysterical stab chords, towards the end. But with characteristic abruptness, Birtwistle's final gesture is a soft one: a bare ninth played quietly in the strings. This piece is an excellent addition to the Birtwistle canon, exuding his odd sense of wit from every skewed melodic line.

The London Sinfonietta are on home territory when playing Birtwistle, especially under the guidance of David Atherton, and their familiarity with his music and his style made for a superb and compelling performance. With the man himself on good form as well, and a solid contribution from Tom Service, this was a truly exemplary musical portrait, whatever the weather.

London Sinfonietta, at Southbank Centre: QEHPaul Kilbey reviews In Portrait: Harrison Birtwistle with Tom Service in discussion with the composer and the London Sinfonietta, at the Southbank Centre.5