It's not often that the Wigmore Hall audience is roused to anti-establishment protest. But Peter Maxwell Davies's introduction to the world premiere of his Third Naxos Quartet - a piece composed, he said, as a response to the invasion of Iraq, which he called "one of the greatest disasters of our time" - inspired an explosion of applause.

The piece - the third of a projected cycle of 10 quartets for the record label Naxos and the Maggini Quartet, who gave the premiere - began life earlier this year as an esoteric study of the relationships between different sets of musical pitches. But this austere process was transformed by Davies's impassioned anti-war feelings. He has turned the string quartet, the medium that supposedly embodies abstract musical logic, into a vehicle for violent imagery.

At the end of the second movement, In Nomine, tremulous violin lines hovered above an austere drone, a "beating of angel's wings", according to the composer. This ethereal music was brought shudderingly to earth with an acerbic transformation of the In Nomine chant as it were to an anti- In Nomine, in other words, "not in our name". In the final Fugue, the Magginis - who played with compelling insight - created a dialogue between ancient and modern, as an archaic-sounding texture was traduced by jagged, dissonant music. In the last moments of the performance, that contrast was amplified, as hollow, stabbing chords exploded over quiet, sinewy lines.

The way Davies transforms his political sentiments into musical structure gives the whole piece a coherent architecture. If anything, his technical manipulation is almost too sophisticated: in the first movement, he composes what he describes as an "empty, grotesque" march, but in the Maggini's performance, the music was expressively intense, but always refined. This is music of mysterious power that does not easily give up its secrets.