Improvisation is often talked about bombastically as an environment in which “anything can happen,” especially up here at the Fringe, where each new show competes in its publicity and press releases to sound wackier and more out-there than the last. Certainly there are shows where the action takes unexpected turns, but much of improvisational comedy is grounded in practice, and has certain rules.
Comedian Thom Tuck  is a former member of both improvisational troupe the Improverts , as well as a regular on late-night improvisation show Voices In Your Head . He's also up at Edinburgh with two shows of his own. “It depends on the format,” he tells me when I ask about the science and preparation involved. “There is short-form and long-form improvisation. Short-form – what the Improverts do, and [sort of] what Voices does, is usually based on games.”
Mike Slater is a founder member of No Shoes Theatre , whose show The Improvised Musical  is currently in its fourth year at the Fringe. They, he tells me, are very much “long-form” improvisation, narrative arc and all, and preparation is key. “The main thing is being around each other a lot, and playing the sort of games that make spontaneity happen. We sit down and talk about how stories are constructed, and songs; what makes a story, what makes a song. We spend ten hours a day together.”
“We know a certain number of things from experience,” he goes on. “Stories are made up of problems and solutions, so we introduce a major problem early on, and try not to introduce them after half-way through. We know that we get about seven songs, and we know that we get about nine scenes. Occasionally we throw all of that out the window. The more we do it together, the more we get a feel for what the other person's doing, where they're going.”
In Voices In Your Head, rather than follow the instructions of a stage presence, or of the audience as in The Improvised Musical, the performers obey The Voice, embodied by Deborah Frances-White, who stands at the back of the auditorium with a microphone. It's her show, so what she says goes – usually.
The Voice is quite antagonistic in tone, and when she picks on Phill Jupitus, who had never been on the show before – performers have no preparation for the show, and don't know what to expect – an extraordinary scenario began to build itself. Improvisation encourages performers whole-heartedly to commit to their first instinctive responses. “What is your name,” asks The Voice, and the performers will come up with one on the spot, in the moment, and build a character and a scenario around these instantaneous associative responses.
This is quite unusual for an improvisation show. More traditional groups practice the games and structures involved before going on stage. “It's fun when you're put on the spot, though,” says Tuck. “You're excited to see where it's going to go.”
One particular episode went very off-piste indeed. A power-struggle developed between The Voice and the character Jupitus was building. The dialogue between the two became faster and faster, angrier and angrier, and more and more intense, and ended with Jupitus advancing through the audience, shirtless and mad-eyed, on an audibly terrified Frances-White at the back, the two of them screaming at each other at the top of their voices, their character arcs locked by Jupitus' responses into that of former lovers. The audience was electrified, The Voice audibly shaken. “This next one,” Tom Salinsky – another of the performers – muttered after the audience and The Voice had both had a chance to settle down. “Is called: Follow That.”
After the show I run into Tuck in the Pleasance's Brookes Bar, and ask if it's always that intense. “It's usually a bit mental,” he replies, “but maybe not that mental.”