He also formed a long-standing partnership with saxophonist Evan Parker, which led to a trio with drummer Paul Lytton which became one of the best-known and most widely travelled free-improvising groups of the 1980s and 1990s.

The result was a series of ambitious, album-length compositions designed to give all the players in the band maximum opportunity for expression, while still preserving a rigorous sense of form: Zurich Concerts (with Anthony Braxton), Harmos, Double Trouble (originally written for an encounter with Alexander von Schlippenbach's Globe Unity Orchestra, though the eventual CD was just for the LJCO), Theoria (a concerto for guest pianist Irène Schweizer), Portraits (a 2-CD set of musical portraits of the band members and their internal groupings), Three Pieces, and Double Trouble Two.

[2] Guy has also written for other large improvising ensembles, such as the NOW Orchestra and ROVA (the piece Witch Gong Game inspired by images by the visual artist Alan Davie).

Guy's session work in the pop field includes playing double bass on the song "Nightporter", from the Japan album Gentlemen Take Polaroids.

Similarly, in his concert works, Guy manages to alternate harmonic and rhythmic complexity worthy of 1960s experimentalists such as Penderecki and Stockhausen with joyous, often ecstatic, melody.

Some of his compositions, such as "Witch Gong Game" for ensemble, use graphic notation in conjunction with cue cards to lead performers into playing and improvising material from numbered sections of the score.