The Gogmagogs are back at the City of London Festival, and yet again have produced an astonishing, virtuosic show - Gogmagogs Gobbledygook - that has pushed back the boundaries of classical music.

The group of seven seriously good string players was set up in 1995 by theatre director Lucy Bailey and violinist Nell Catchpole. Bailey wanted to see what would happen if you took away the stands from players and unlocked the physicality and visual element of musical performance.

Working with composers, and via an intense collaborative process, the Gogs developed an entirely individual creative form, that combined music, dance and drama. Gobbledygook has taken the experiment a stage further, by involving writers and playwrights in the process. Without a hint of respect for the traditional distinctions between creative professions, the Gogs have added acting to their repertoire of skills.

The show consists of five pieces that just about contain individual narratives, but are hopped between randomly as if the audience were channel-surfing. The best and most coherent of them, How to Deal with Being Dumped by Patrick Barlow and Django Bates, is a brilliantly funny tale of dealing with a failed love affair in "eight easy movements" - the movements being those of a traditional Requiem. It all makes perfect sense, really - the dies irae is when you got really furious with the woman who left you; the recordare, or day of reckoning, is when you divide your belongings.

David Lasserson makes a splendid jilted viola player (it would be the viola). The whole piece is framed as a game show, with Nell Catchpole a Cilla-like hostess. The music exists seamlessly alongside the dialogue and movement - sometimes it mimics the rhythm of speech, sometimes it almost finishes sentences without the need for words. Sometimes it straightforwardly describes a mood or else a verbal reference (as in "it takes two to tango") cues in a musical joke.

It will be interesting to see whether the Gogmagogs' work can be sustained and developed further without their new form of performance straining or becoming stale. But just now their show is a delight. And worth seeing just to check out how a double bass player fares when playing lying down.