We are all familiar with the blight of unfinished projects in our lives: half-filled diaries, abandoned computer folders, sun-faded membership cards, pathetic relics of our idealistic pasts. When cellist and composer Peter Gregson wrote and released the first two instalments of his “quartet of string quartets” concept in 2016 and 2017, and then allowed his blossoming career in scoring and composition to distract him from its completion, nobody could have blamed him for never returning to finish it. Rejoice, then, and slightly resent him, as five years on, he returns with the third and fourth parts of this sprawling series.

‘Quartets: Three’ finds him building on the electronic and synthesised texturing that he began adding to the base string quartet ingredients in the second part, even if you have to gently arch your ear towards the music to perceive the added flourishes at times. The writing takes centre stage, from the endearing ‘Cantus’, its melody a tide gentle lapping to the piece’s ancient rhythm, to ‘Murmuration’, which, like the titular flock, moves with a logic and grace that, when observed, defies prediction or clear pattern, but dances with such effortless elegance that it is understood at a deeply satisfying level.

The grand, lachrymose timbre of swelling cello rises to the fore in ‘Even’, while the four-headed beast that we know to possess fearsome power exercises stately restraint. The clipping and popping of plucked, taut strings in ‘Up’ conjure a playful scramble in the overgrowth, nudged only gently by the assembled atmosphere of electronics, more an augmented background setting, a mise-en-scene.

With ‘Quartets: Four’, Gregson returns to the magnificent simplicity of the four string instruments. Over its three movements, the fragility is raw, the tension is high and the humanity of the players is foregrounded. You hold your breath as the second piece opens delicately, but you soon lose any further sense of your own actions in the face of the rich, nutritive, grounded assurance of the arrangement. Gregson has been shown throughout his career to have a fine grasp on the establishment traditions, a basis from which he has often jumped off into creative new tangents. But with these two new collections, he reminds us that even with just that bare essence, that foundry of classical music, the string quartet, he remains a modern master.