To celebrate Philip Glass' 80th birthday, the BBC honoured him with one their invaluable Total Immersion days, of which this concert was the climax. Glass has had a very mixed press over his long career. After a strong musical training, which included lessons with Darius Milhaud and Nadia Boulanger, he proceeded to eschew both traditional harmonic procedures as well as the predominant serialism of the time in the 1950s and 1960s. Instead he developed a new style which relied on the basic building blocks of Western music, imbued with the cyclic rhythms of the Indian raga learnt from working with Ravi Shankar. Repetition of simple phrases and harmonic blocks, as well as a rhythmic regularity became the new Minimalism. In many ways, the most radical and lasting of the post-war innovations in classical music, although not recognised as such at the time. Initially critics and the public found the style retrograde and baffling, but somehow it wouldn’t go away. Other composers developed the oeuvre in different directions, but Glass’ music has always remained at the centre of the movement.

Glass’ style has developed over the decades though and this concert gave us some evidence of these changes. The opening piece the Prelude to Act 1 to his 1983 opera Akhnaten, is a pure version of middle period Glass. Its simple arpeggios going through a process of evolution that creates its own sense of time and ritual. Marin Alsop and the BBCSO knew exactly how to capture the hypnotic quality of the piece, constantly alert to the rhythmic security and accurate in the filigree harmonic outlines.

Next up was the UK première of the Concerto for Two Pianos and Orchestra written for the flamboyant duo Katia and Marielle Labèque in 2015. A work that encapsulates the late Glass style, adopting less time stretching repetition and more conventional variety of material, even though this material on the new concerto still remains disconcertingly other worldly at times. The first movement pulls us directly into a highly-strung world of clotted orchestration and rhythmic complexity, which virtually subsumes the soloists into the melee. Sometimes the thick textures were reminiscent of Milhaud. Alsop and the BBCSO were again exceptional in their alertness to the rhythmic pulse. The Labèque sisters finally got to break free towards the end of the movement when a gentler mood takes over.

In the mystifying second movement, elements of dance are thrown together producing a tone somewhere between humour and sarcasm. Again, Alsop was alert to all these more rapid mood changes and the Labèques’ were given more of the spotlight and were able to characterise much of the music. Leaving a slight unpleasant taste in the mouth, the progress to a more familiar, gentler Glass idiom was satisfying and in the final movement the composer finally allowed something more coherent and more straightforwardly constructed. The soloists were given gentle and pleasing exchanges and a touching simplicity was achieved in the final bars. Baffling and opaque overall on first hearing, I shall be listening to the concerto again on Tuesday when the BBC broadcasts the concert to celebrate the composer’s actual birthday, to see if it makes more impact the second-time round.

Itaipu made a lot more sense from the outset. Combining the purity of purpose of earlier works like Akhnaten it introduced more variety into the mix. Setting a text in the language of the Brazilian Guarani tribe about the Parana river that they believe is the birthplace of music, Itaipu is a vigorous and dramatic depiction of the landscape and mystical qualities of the river and the eponymous dam that traps it on its course. Here the BBC Chorus clearly enjoyed the grateful, and often full throated, parts written for them. Alsop marshalled her forces with the generous aplomb we have come expect from her and this entertaining work, surely one of the composer best concert pieces, was a delight from beginning to end.