Reading Gérard Grisey’s programme notes on his masterpiece Vortex Temporum is not the most agreeable experience. The reader is informed that the work is structured around ‘three basic forms’: ‘the original event – a sinusoidal wave – and two continuous events, an attack with or without resonance as well as a sound held with or without crescendo’. It transpires that there is also an ‘imagined microscope’, thanks to which ‘the notes become sound, a chord becomes a spectral complex, and rhythm transforms into a wave of unexpected duration’.

I don’t know what any of this means, and I have read it several times. Presumably it meant something fairly specific to Grisey, but what he really hoped to communicate through writing it down is lost to me. I enjoyed the piece, though; that was great.

That Grisey was very intelligent is clear enough from the quotations above. What may be less obvious – and the same goes here with regard to any number of other ‘difficult’ composers – is that Grisey’s obsession with dryness and inscrutability in prose is completely at odds with the incredible richness and warmth of his music.

Vortex Temporum may well have been composed using any number of arcane and complex formulae, but what concerned Grisey – possibly all that concerned Grisey – was the sound that his experiments produced. The work’s three movements each unfolded with an impossibly sure sense of structure, exploding the opening notes into strange, beautiful forms. On Monday, these huge and bizarre blocks of sound filled Shoreditch Church, courtesy of London Contemporary Orchestra with conductor Hugh Brunt, as part of the Spitalfields Winter Music Festival. It was an impeccable performance of a draining, epic, enthralling piece.

Grisey makes much use of microtonal tunings in the piece, even requiring adjustments to the piano, but it was remarkable how organically integrated the quarter- and eighth-tones were into the sound. Harmonically the piece came across as a radical extension of the soundworld of Ravel – from whom the opening sonority was borrowed – and perhaps also Ligeti, a teacher of Grisey's. Ligeti may also be a point of reference for the performative self-awareness of this work. Pushing constantly at the limits of the audible or comprehensible, Grisey frequently requires his string players (single violin, viola and cello) to bow silently or almost-silently, as if straining for something impossible, producing little more than the sound of the bow brushing against the string.

A couple of times, this odd, ecstatic gesture followed enormous, thick crescendi, surprisingly forming moments of real theatricality. Grisey’s concern for the effect of his piece – both musical and dramatic – was never in doubt, and the incredible polish of LCO’s performance enhanced this enormously. A standout moment was the first movement’s long, insanely testing piano solo, played meticulously and energetically by Antoine Françoise. Incredibly detailed and intense, this solo climaxed with enormous, shocking cluster chords. It was something like a musical version of Lucky’s long soliloquy in Waiting for Godot, but as if all of Lucky’s frantic phrases were anagrams of each other.

Brunt was a confident, calming figure conducting the ensemble through this work. London Contemporary Orchestra have created a space in which the maddest music can be taken seriously, and the passion for Grisey’s piece that the performers clearly felt was infectious.

The concert had opened with Claude Vivier’s gamelan-inspired Pulau Dewata, performed on viola, cello, piano and vibraphone. I was surprised to learn later that Vivier did not specify scoring for this piece, and that this instrumentation must have been the ensemble’s choice. The combination chosen of vibraphone and piano was extremely distinctive, and these parts intermingled and merged throughout, their closeness exaggerated by the church’s acoustic. Pulau Dewata is a very linear, almost improvisational piece a little like Messiaen in effect. It was given an exemplary performance, albeit one coloured considerably by the choice of instruments.

LCO were joined after this by violinist Agata Szymczewska for the world première of Martin Suckling’s de sol y grana. The piece’s nine ‘little bubbles of music’ floated enchantingly about, showcasing the virtuosity of all involved. There was something very Second-Viennese-School about the composition: the orchestration had a Schoenbergian precision of colour, and the integration of tonal sounds into the deep texture recalled Berg. Overall, though, it was Pierre Boulez whom it may have owed the most to, in its combination of rigour and sonic beauty – and through this it formed some connection with the Grisey piece which followed. Suckling has created a remarkable and beautiful work in de sol y grana, and it deserves more performances. That given by Szymczewska was delicate and poetic, and clear enough to let the music sing through all the rapid scales and double-stops.

This was a concert of challenging, valuable music, programmed with bravery and performed with verve. It’s hard to fault the LCO, apart from for letting those programme notes go to print.