Its rise was made possible by a growing sense of belonging to a community among London-based free improvisers. The late '90s saw free improv become more accepted as a genre, however it remained marginalized, for better or worse. A younger, eager generation was following the footsteps of pioneers like Derek Bailey, Evan Parker, and Steve Beresford. The LIO became a home where experienced players and students met to tackle listening issues in a large group environment. The playful nature of their monthly encounters at the Red Rose Club allowed the music to develop spontaneously and without ego clashes getting in the way. The group performs collective free improvisations and structured improvisations composed by some of its members.

The LIO has its roots in a tour of Britain by Lawrence Butch Morris' London Skyscraper project in November 1997. Organized by the Contemporary Music Network, the tour featured many musicians from the London Music Collective serving under Morris' directorial baton. Some of the musicians liked the concept of group improvisation and wanted to explore it in different directions. Beresford, Parker, and a young trumpeter named Ian Smith recruited a number of participants and by mid-1998, a group of 20 to 30 improvisers performed public rehearsals once a month at the Red Rose Club. The lineup varied then and would continue to fluctuate depending on availability and interest. The LIO is open to kindred spirits regardless of age, experience, and origin (it has welcomed visiting musicians like Greek cellist Nikos Veliotis and Swiss viola player Charlotte Hug), as long as everyone checks his or her ego at the door. Regular participants and contributing composers include Beresford, Parker, Veryan Weston, Caroline Kraabel, Simon H. Fell, Adam Bohman, Dave Tucker, Philipp Wachsmann, Pat Thomas, and Terry Day, who found the familial atmosphere conducive enough to bring him out of a ten-year retirement (due to illness) and resume performing in public.

The record label Emanem's owner, Martin Davidson, quickly stepped in to document the growth of the LIO. Proceedings (2000) was recorded about one year after the group's debut and featured 31 players. On The Hearing Continues (2001), a year later, the orchestra comprised 37 musicians. Davidson included the LIO in the program of his first Freedom of the City festival in May 2001. A group of 39 can be heard on the two-CD set Freedom of the City 2001: Large Groups (2002). ~ François Couture